JP2005222968A - Surface-emitting laser, wavelength-variable surface-emitting laser device using the same, and method for controlling emission wavelength in surface-emitting laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a surface-emitting laser for changing the emission wavelength speedily over a wide wavelength range, and to provide a wavelength-variable surface-emitting laser device, and to provide a method for controlling the emission wavelength of the surface-emitting laser. <P>SOLUTION: A lower distribution reflection layer is provided between a semiconductor substrate and an active layer, an upper distribution reflection layer is provided at the upper side of the active layer via an air gap, an optical resonator is formed by the upper distribution reflecting layer and the lower distribution reflecting layer, and the surface-emitting laser for emitting laser beams in perpendicular direction to the semiconductor substrate is improved. The surface-emitting laser has a refractive index control unit that is provided inside an optical resonator and has a refractive index layer, in which the refractive index is changed. Then, the upper distribution reflecting layer is formed by a semiconductor micromachining technique and can move in the vertical directions. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention has a lower distributed reflective layer between a semiconductor substrate and an active layer, and an upper distributed reflective layer is provided above the active layer via an air gap, and optical resonance occurs between the upper distributed reflective layer and the lower distributed reflective layer. The present invention relates to a surface emitting laser that forms a laser and emits laser light in a direction perpendicular to a semiconductor substrate, a wavelength tunable surface emitting laser device using the surface emitting laser, and a surface emitting laser oscillation wavelength control method. The present invention relates to a wavelength-tunable surface-emitting laser capable of changing the oscillation wavelength at high speed, a wavelength-tunable surface-emitting laser device using the surface-emitting laser, and an oscillation wavelength control method for the surface-emitting laser.

  2. Description of the Related Art A surface emitting laser (VCSEL: Vertical Cavity Surface Emitting Laser) has a structure in which a semiconductor layer is sandwiched between distributed reflection layers formed of a multilayer film or the like. 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. Such a surface emitting laser is used as a light source for optical communication or a light source for optical measurement. For this reason, development of a wavelength-tunable surface emitting laser capable of changing the oscillation wavelength is demanded.

  FIG. 5 is a structural cross-sectional view showing an example of a conventional surface emitting laser that is tunable over a wide range (see, for example, Patent Document 1). In FIG. 5, an n-type InP substrate 10 is a semiconductor substrate, and a laser light extraction port is formed by etching. The lower DBR (Distributed Bragg Reflector) layer 11 is a lower distributed reflection layer, and is formed on the substrate 10 and has a multilayer structure such as n-type InGa (Al) As / InAlAs. InGa (Al) As having a high refractive index, a small amount (a few%) of Al is added to widen the band gap and prevent light absorption. The lower spacer layer 12 is made of, for example, n-type InAlAs and is formed on the lower DBR layer 11 to adjust the optical distance between the lower DBR layer 11 and the active layer 13.

  The active layer 13 is made of, for example, InGaAlAs and is formed on the lower spacer layer 12, and a multi quantum well or the like is used. The upper spacer layer 14 is formed on the active layer 13 with, for example, p-type InAlAs. The upper electrode 15 is formed on the upper spacer layer 14 with the central portion removed to extract laser light.

  The dielectric multilayer mirror 16 is an upper distributed reflection layer, and is made of, for example, SiO 2 / TiO 2 and is formed above the upper spacer layer 14 without being in contact with the upper spacer layer 14. An optical resonator is formed between the lower DBR layer 11 and the dielectric multilayer mirror 16. The air gap AG is a space between the upper spacer layer 14 and the dielectric multilayer mirror 16. The lower electrode 17 is formed on the lower side (back surface) of the substrate 10.

  The membrane 18 is made of, for example, Si, and the dielectric multilayer mirror 16 is deposited on the lower side (which will be the surface when the substrate of the membrane 18 is processed, but will be described in the direction in FIG. 5 after bonding). The membrane 18 is a MEMS (micro electro-mecanical system: a micro mechanical system in which movable parts and electronic circuits are integrated by a semiconductor micromachining technology), and is movable in the vertical direction.

A method for manufacturing such a surface emitting laser will be described.
A lower DBR layer 11, a lower spacer layer 12, an active layer 13, and an upper spacer layer 14 are sequentially formed on the substrate 10 by metal organic vapor phase epitaxy (MOVPE). Then, the upper electrode 15 with the center removed in a circular shape is formed on the upper spacer layer 14 by using a photolithography method and a lift-off method. In addition, the substrate 10 is etched to the lower surface of the lower DBR layer 11 to form a circular light extraction port at the center. A lower electrode 17 is formed on the back surface of the remaining substrate 10.

  On the other hand, a membrane 18 is formed on a Si substrate (not shown) separately from the compound semiconductor, and a dielectric multilayer mirror 16 is deposited on the lower side.

  Then, the electrode 15 provided on the upper spacer layer 14 is bonded to a Si substrate (not shown) (for example, solder or adhesive).

Next, the operation of the conventional example shown in FIG. 5 will be described.
First, an operation for emitting laser light will be described.
When a voltage is applied between the upper electrode 15 and the lower electrode 17, current flows from the upper electrode 15 to the lower electrode 17 through the upper spacer layer 14, the active layer 13, the lower spacer layer 12, the lower DBR layer 11, and the substrate 10. Flows.

  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 above-described optical resonator and is extracted from the outlet of the substrate 10 (that is, the back surface of the substrate 10). It is emitted as laser light.

  In FIG. 5, since the injected current flows from the upper electrode 15 toward the lower electrode 17, it is injected from the vertical direction of the active layer 13 which is the light emitting region, but the current is injected from the lateral direction of the light emitting region. It doesn't matter.

  In this way, an optical resonator is formed by the lower DBR layer 11 formed on the compound semiconductor substrate 10 and the dielectric multilayer mirror 16 bonded to the upper side of the active layer 13 via the air gap AG. It functions as a surface emitting laser.

Next, an operation for changing the oscillation wavelength will be described.
When a voltage is applied to an electrode provided on a Si substrate (not shown), an electrostatic force is generated. The membrane 18 moves up and down using this electrostatic force as a driving force. That is, since the dielectric multilayer mirror 16 also moves up and down, the optical resonator length (that is, the interval between the optical resonators) changes, and the oscillation wavelength is changed.

  Next, a conventional example of a surface emitting laser that changes the oscillation wavelength without providing the air gap AG will be described. FIG. 6 is a cross-sectional view showing another example of a conventional surface emitting laser (see, for example, Patent Document 2). On the semiconductor substrate 20, a lower DBR layer (lower distributed reflective layer) 21, a lower spacer layer 22, an active layer 23, an upper spacer layer 24, a contact layer 25, a multiple quantum well layer 26, an upper DBR layer (upper distributed reflective layer) 27) is formed.

  Here, the multiple quantum well layer 26 is a refractive index control layer. The absorption edge wavelength of the multiple quantum well layer 26 is shorter than the absorption edge wavelength of the active layer 23.

  Further, the periphery of the upper DBR layer 27 and the multiple quantum well layer 26 is etched up to the contact layer 25 except for the central portion that emits surface light. Then, upper electrodes 28a and 28b are provided on the upper DBR layer 27 and the contact layer 25, respectively, and a lower electrode 29 is provided on the back surface of the substrate.

The operation of the conventional example shown in FIG. 6 will be described.
A voltage is applied to the upper electrode 28b and the lower electrode 29 so that the upper electrode 28b has a high potential. As a result, a current flows from the upper electrode 28b to the lower electrode 29, laser oscillation occurs in the active layer 23, and laser light is emitted.

  Here, when a predetermined voltage that is lower than the upper electrode 28b is applied to the upper electrode 28a and an electric field is applied to the multiple quantum well layer 26, multiple quantum wells are generated by a quantum confined Stark effect. The refractive index of layer 26 changes. This changes the effective optical path length of the optical resonator and changes the oscillation wavelength.

JP 2003-318485 A (paragraph number 0025-0067, FIG. 1-3) Japanese Patent Laid-Open No. 6-188518 (paragraph number 0011-0028, FIG. 1-3)

  Since the surface emitting laser having the structure shown in FIG. 5 has the air gap AG, the dielectric multilayer mirror 16 can be moved largely up and down (that is, the interval of the air gap AG can be changed). As a result, the oscillation wavelength can be continuously changed over a wide wavelength range (for example, several tens [nm]) as compared with the surface emitting laser shown in FIG. 6 having no air gap AG, and operates as a wavelength tunable surface emitting laser. can do.

  However, since the membrane 18 is mechanically moved by electrostatic force, it takes a few [ms] to change the oscillation wavelength, and there is a problem that it is very slow. This will be described with reference to FIG. FIG. 7 is a diagram showing characteristics when the oscillation wavelength of the surface emitting laser shown in FIG. 5 is changed. In FIG. 7, the horizontal axis is time, and the vertical axis is the oscillation wavelength. The wavelength λ0 is the current wavelength, the wavelength λ1 is the target oscillation wavelength, and the target wavelength range λs is the wavelength range of ± Δλ of the target oscillation wavelength λ1. Usually, the time until the oscillation wavelength of the surface emitting laser falls within the target wavelength range λs is called a change time (or switching time).

  As shown in FIG. 7, when the membrane 18 is moved at a high speed to a position where the target oscillation wavelength λ1 is reached, large hunting occurs, causing oscillation wavelength fluctuation over a long period of time, and the time until it falls within the target wavelength range λs. It takes. Conversely, if the membrane 18 is moved at a low speed, hunting hardly occurs, but it still takes time until it falls within the target wavelength range λs. Even if the speed at which the membrane 18 is moved is optimized, there is a problem that it takes a few [ms] for the oscillation wavelength fluctuation to fall within the target wavelength range λs, and the change of the oscillation wavelength is very slow.

  On the other hand, since the surface emitting laser having the structure shown in FIG. 6 electrically changes the refractive index of the multiple quantum well layer 26, the oscillation wavelength can be changed at high speed (for example, several [ns]).

  However, since the amount of change in the refractive index is limited, there is a problem that the wavelength range in which the oscillation wavelength can be changed is as narrow as several [nm].

  Accordingly, an object of the present invention is to realize a surface emitting laser capable of changing the oscillation wavelength at high speed over a wide wavelength range, a wavelength tunable surface emitting laser device using the surface emitting laser, and a method for controlling the oscillation wavelength of the surface emitting laser. There is.

The invention described in claim 1
A lower distributed reflective layer is provided between the semiconductor substrate and the active layer, an upper distributed reflective layer is provided above the active layer via an air gap, and an optical resonator is formed by the upper distributed reflective layer and the lower distributed reflective layer. A surface emitting laser that emits laser light in a direction perpendicular to the semiconductor substrate,
A refractive index control unit having a refractive index control layer provided inside the optical resonator and having a refractive index that changes,
The upper distributed reflection layer is formed by a semiconductor microfabrication technique and is movable in the vertical direction.

The invention according to claim 2 is the invention according to claim 1,
The refractive index control unit is provided in contact with the air gap.

The invention according to claim 3 is the invention according to claim 1 or 2,
The refractive index control unit is monolithically integrated on the surface of the compound semiconductor having at least the active layer and the lower distributed reflection layer.

The invention according to claim 4 is the invention according to claim 1 or 2,
The refractive index control unit is formed in a separate chip from each of the compound semiconductor having at least the active layer and the lower distributed reflective layer and the upper distributed reflective layer, and is bonded to the surface of the compound semiconductor or the upper distributed reflective layer. It is characterized by that.

The invention according to claim 5 is the invention according to any one of claims 1 to 4,
The refractive index control layer of the refractive index control unit is a semiconductor junction layer whose refractive index changes by current injection or voltage application.

The invention according to claim 6 is the invention according to any one of claims 1 to 4,
The refractive index control unit has a Schottky electrode,
The refractive index control layer of the refractive index control unit is bonded to the Schottky electrode to form a semiconductor-metal Schottky junction, and the refractive index is changed by voltage application.

The invention according to claim 7 is the invention according to any one of claims 1 to 4,
The refractive index control unit has a MIS structure electrode composed of an insulator and a metal,
The refractive index control layer of the refractive index control unit is bonded to the MIS structure electrode, and changes the refractive index when a voltage is applied.

The invention according to claim 8 is the invention according to any one of claims 1 to 7,
The refractive index control unit is characterized by reducing oscillation wavelength fluctuation caused by movement of the upper distributed reflection layer in the vertical direction.

The invention according to claim 9
A surface emitting laser according to any one of claims 1 to 8,
An oscillation wavelength fine adjustment circuit that changes the oscillation wavelength of the surface emitting laser by controlling the refractive index of the refractive index control unit of the surface emitting laser according to the wavelength of the laser light from the surface emitting laser,
An oscillation wavelength rough adjustment circuit that changes an oscillation wavelength of the surface emitting laser by controlling a vertical position of the upper distributed reflection layer of the surface emitting laser, and the oscillation wavelength fine tuning circuit includes the upper distributed reflection It is characterized in that oscillation wavelength fluctuations caused by movement of the layer in the vertical direction are reduced.

The invention according to claim 10 is:
In the surface-emitting laser oscillation wavelength control method according to any one of claims 1 to 8,
The upper distributed reflection layer of the surface emitting laser is moved up and down to change the interval between the optical resonators to change the oscillation wavelength, and the refractive index of the refractive index control unit of the surface emitting laser is changed to change the optical resonator. The oscillation wavelength is changed by changing the effective optical path length.

The invention according to claim 11
In the surface-emitting laser oscillation wavelength control method according to any one of claims 1 to 8,
Change the oscillation wavelength by moving the upper distributed reflection layer of the surface emitting laser in the vertical direction to change the interval between the optical resonators,
Depending on the wavelength of the laser light from the surface emitting laser, the refractive index of the refractive index control unit of the surface emitting laser is changed to change the effective optical path length of the optical resonator, so that the upper distributed reflection layer is moved in the vertical direction. It is characterized in that the oscillation wavelength fluctuation generated by the movement of is reduced.

The present invention has the following effects.
According to the first to eighth aspects, the upper distributed reflection layer moves in the vertical direction to change the oscillation wavelength over a wide wavelength range, and the refractive index control unit sets the oscillation wavelength at a high speed independently of the upper distributed reflection layer. change. Furthermore, oscillation wavelength fluctuations caused by the vertical movement of the upper distributed reflection layer are reduced. Thereby, the oscillation wavelength can be changed at high speed over a wide wavelength range.

  In addition, even if the upper distributed reflection layer moves in the vertical direction due to the influence of the usage environment (for example, vibration, temperature fluctuation, impact), the refractive index control unit can quickly oscillate the oscillation wavelength independently of the upper distributed reflection layer. change. Furthermore, since the refractive index control unit reduces oscillation wavelength fluctuations caused by the movement of the upper distributed reflection layer in the vertical direction, it is possible to emit laser light having a stable wavelength.

  According to the third aspect, since the refractive index control unit is monolithically integrated, it can be produced at a low cost.

  According to the fourth aspect, since the refractive index control unit is not monolithically integrated on the surface of the compound semiconductor, but is formed and bonded as a separate chip, it is not necessary to consider lattice matching with the surface of the compound semiconductor. As a result, the selection range of the material is widened, and the refractive index control unit can be formed of an optimum material.

  According to the ninth aspect, the oscillation wavelength coarse adjustment circuit changes the oscillation wavelength by moving the upper distributed reflection layer of the surface emitting laser in the vertical direction. The oscillation wavelength fine adjustment circuit changes the refractive index of the refractive index control unit based on the wavelength of the laser light from the surface emitting laser, and reduces oscillation wavelength fluctuations caused by the vertical movement of the upper distributed reflection layer. To do. Thereby, the oscillation wavelength can be changed at high speed over a wide wavelength range.

  Even if the upper distributed reflection layer moves in the vertical direction due to the influence of the use environment, the oscillation wavelength fine adjustment circuit changes the refractive index of the refractive index control unit based on the wavelength of the laser light from the surface emitting laser. As a result, the oscillation wavelength fluctuation caused by the movement of the upper distributed reflection layer in the vertical direction is reduced, so that laser light with a stable wavelength can be emitted.

  According to the tenth aspect, the upper distributed reflection layer of the surface emitting laser is moved in the vertical direction, and the oscillation wavelength is changed by changing the refractive index of the refractive index control unit. Thereby, the oscillation wavelength can be changed at high speed over a wide wavelength range.

  According to the eleventh aspect, the oscillation wavelength is changed by moving the upper distributed reflection layer of the surface emitting laser in the vertical direction. In addition, the refractive index of the refractive index control unit is changed based on the wavelength of the laser light from the surface emitting laser, thereby reducing oscillation wavelength fluctuations caused by the vertical movement of the upper distributed reflection layer. Thereby, the oscillation wavelength can be changed at high speed over a wide wavelength range.

  Further, even if the upper distributed reflection layer moves in the vertical direction due to the influence of the usage environment (for example, vibration, temperature fluctuation, impact), the refractive index of the refractive index control unit is changed to move the upper distributed reflection layer in the vertical direction. Since the oscillation wavelength fluctuation generated by the movement of the laser beam is reduced, it is possible to emit a laser beam having a stable wavelength.

Embodiments of the present invention will be described below with reference to the drawings.
[First embodiment]
FIG. 1 is a structural sectional view showing a first embodiment of the present invention. Here, the same components as those in FIG.
In FIG. 1, a separation layer 19 is newly formed on the surface of a compound semiconductor composed of the lower DBR layer 11 and the active layer 13 (in FIG. 1, the surface of the upper spacer layer 14 serving as an epi layer of the compound semiconductor). The The isolation layer 19 performs electrical insulation, and is, for example, a pn junction layer or a high resistance layer.

  A refractive index control unit 30 is newly provided in contact with an air gap AG inside the optical resonator formed by the lower DBR layer 11 and the dielectric multilayer mirror 16. The refractive index control unit 30 includes an n-type contact layer 31, a multiple quantum well layer 32, a p-type contact layer 33, an upper electrode 34 for refractive index control, and a lower electrode 35 for refractive index control.

  The n-type contact layer 31 is formed on the separation layer 19. The separation layer 19 electrically insulates the compound semiconductor that emits laser light from the refractive index control unit 30. The multiple quantum well layer 32 is formed on the n-type contact layer 31. Here, the multiple quantum well layer 32 is a refractive index control layer. In addition, the absorption edge wavelength of the multiple quantum well layer 32 is shorter than the absorption edge wavelength of the active layer 13. That is, the multiple quantum well layer 32 has a band cap that is transparent to the oscillation wavelength of the active layer 13.

  The p-type contact layer 33 is formed on the multiple quantum well layer 32. The upper electrode 34 for controlling the refractive index is formed on the p-type contact layer 33 with the central portion removed to extract laser light. The lower electrode 35 for controlling the refractive index is formed on the periphery of the n-type contact layer 31 from which the multi-quantum well layer 32 and the p-type contact layer 33 are removed by mesa processing.

A method for manufacturing such a surface emitting laser will be described.
Lower DBR layer 11, lower spacer layer 12, active layer 13, upper spacer layer 14, separation layer 19, n-type contact layer 31, multiple quantum well layer 32, p-type by metalorganic vapor phase epitaxy on substrate 10 The contact layers 33 are sequentially epitaxially grown. Thereafter, except for the portion where the light extraction port is formed, the peripheral portions of the n-type contact layer 31, the multiple quantum well layer 32, and the p-type contact layer 33 are etched and mesa processed. The n-type contact layer 31 is etched halfway.

  Then, the upper electrode 34 for controlling the refractive index, the center of which is removed in a circular shape, is formed on the p-type contact layer 33. A lower electrode 35 for controlling the refractive index is formed on the periphery of the n-type contact layer 31.

  Further, after etching the n-type contact layer 31 and the separation layer 19 in the peripheral portion, the upper electrode (for laser diode) whose center is removed in a circular shape on the upper spacer layer 14 by using a photolithography method and a lift-off method. ) 15 is formed. In addition, the substrate 10 is etched to the lower surface of the lower DBR layer 11 to form a circular light extraction port at the center. A lower electrode (for laser diode) 17 is formed on the back surface of the remaining substrate 10.

  On the other hand, a membrane 18 is formed on a Si substrate (not shown) separately from the compound semiconductor, and a dielectric multilayer mirror 16 is deposited on the lower side.

  Then, the electrode 15 on the compound semiconductor with the refractive index control unit 30 and a Si substrate (not shown) are bonded together (for example, solder or adhesive) to form an air gap AG.

Next, the operation of the surface emitting laser shown in FIG. 1 will be described.
Since the operation for emitting laser light is the same as that of the surface emitting laser shown in FIG. 5, the description is omitted, and the operation for changing the oscillation wavelength will be described. FIG. 2 is a diagram showing characteristics when the oscillation wavelength of the surface emitting laser shown in FIG. 1 is changed. Here, the same components as those shown in FIG. In FIG. 2, the horizontal axis is time, and the vertical axis is the oscillation wavelength. The wavelength range λ2 is a wavelength range in which the refractive index control unit 30 can change the wavelength. FIG. 2A shows the contribution of the change in oscillation wavelength caused by moving the membrane 18 and the dielectric multilayer mirror 16 up and down by MEMS, that is, when the oscillation wavelength is changed without using the refractive index control unit 30. It is the figure which showed the example of. FIG. 2B is a diagram showing an example of the contribution of the oscillation wavelength change by changing the refractive index of the multiple quantum well layer 32 of the refractive index control unit 30. FIG. 2C shows a characteristic example of the oscillation wavelength of the laser light emitted from the surface emitting laser.

  When a voltage is applied to an electrode provided on a Si substrate (not shown), an electrostatic force is generated. The membrane 18 moves up and down using this electrostatic force as a driving force. That is, since the dielectric multilayer mirror 16 also moves up and down, the interval between the optical resonators changes, and the oscillation wavelength is changed. When moving the membrane 18 to a position where the target oscillation wavelength λ1 is obtained, it is preferable to move the membrane 18 at a speed at which hunting is fastest within the wavelength range λ2, as shown in FIG.

  Further, while the membrane 18 moves up and down, a voltage is applied to the upper electrode 34 for refractive index control and the lower electrode 35 for refractive index control provided in the refractive index control unit 30, so that an electric field is applied to the multiple quantum well layer 32. Is applied by quantum confinement Stark effect (for example, see Shunichi Tanaka, two others, "Optoelectronic Glossary of Terms", 1st edition, Ohm Co., Ltd., November 1996, p567). The wave function of the electrons and holes confined in and the quantum well order change. Therefore, as the applied voltage increases, the exciton absorption peak shifts to the longer wavelength side, and the refractive index of the multiple quantum well layer 32 changes. This changes the effective optical path length of the optical resonator and changes the oscillation wavelength. At this time, as shown in FIG. 2B, the oscillation wavelength is changed in a direction opposite to the oscillation wavelength fluctuation generated by the vertical movement of the dielectric multilayer mirror 16. That is, the change of the oscillation wavelength over a wide wavelength range by the refractive index control unit 30 and the high-speed change of the oscillation wavelength by the dielectric multilayer mirror 16 are performed separately.

  Therefore, the dielectric multilayer mirror 16 is moved up and down by MEMS to change the interval between the optical resonators to change the oscillation wavelength, and the refractive index of the refractive index control unit 30 is changed to effectively change the optical resonator. The oscillation wavelength is changed by changing the appropriate optical path length. As a result, as shown in FIG. 2C, the oscillating wavelength of the surface emitting laser is canceled within the hunting state and quickly falls within the target wavelength range λs (= λ1 ± Δλ).

  In this way, the dielectric multilayer mirror 16 moves in the vertical direction to greatly change the oscillation wavelength over a wide wavelength range. In addition, the refractive index control unit 30 changes the oscillation wavelength at high speed independently of the change of the oscillation wavelength by the dielectric multilayer mirror 16. Further, the refractive index control unit 30 reduces oscillation wavelength fluctuations caused by the vertical movement of the dielectric multilayer mirror 16. Thereby, the oscillation wavelength can be changed at high speed (for example, several [μs]) over a wide wavelength range.

  Further, since the refractive index control unit 30 is monolithically integrated, it can be produced at a low cost.

[Second Example]
There are various surface emitting laser structures in addition to the configuration shown in FIG. 1, but the present invention can be applied to a surface emitting laser having an air gap inside the optical resonator. Then, the 2nd Example of this invention is shown. FIG. 3 is a structural sectional view showing a second embodiment of the present invention. Here, the same components as those in FIG. Since the surface emitting laser shown in FIG. 1 uses p-type for the upper spacer layer 14, the element resistance is high and the light absorption is also large. Therefore, this is an example in which the present invention is applied to a surface emitting laser having an increased n-type region.

  In FIG. 3, between the p-type upper spacer layer 14 and the upper electrode 15, a tunnel junction layer 40 of high-concentration p-type InGaAsP or InGaAlAs, a tunnel junction of high-concentration n-type InGaAs, or the like in order from the bottom. A layer 41, a spacer layer 42 such as n-type InGaAsP, and a contact layer 43 such as n-type InGaAsP are provided. The ion implantation region 44 is provided in the periphery of the upper spacer layer 14 and the tunnel junction layers 40 and 41.

  Then, the separation layer 19 and the refractive index control unit 30 are formed on the surface of the compound semiconductor (in FIG. 3, the upper surface of the contact layer 43 serving as an epi layer of the compound semiconductor).

A method for manufacturing such a surface emitting laser will be described. Differences from FIG. 1 will be mainly described.
A lower DBR layer 11, a lower spacer layer 12, an active layer 13, and an upper spacer layer 14 are formed on the substrate 10 by metal organic vapor phase epitaxy. A p-type tunnel junction layer 40 and an n-type tunnel junction layer 41 are sequentially formed on the upper spacer layer 14 to form a tunnel junction.

  In this state, the central portion is masked, and heavy elements (for example, oxygen, fluorine, silicon, iron, aluminum, chromium, or a combination thereof) in other regions (peripheral portions) are applied to the upper spacer layer 14. Ions are implanted until the resistance is reached, thereby forming an ion implantation region 44 having a high resistance.

  Thereafter, an n-type spacer layer 42, a contact layer 43, a separation layer 19, an n-type contact layer 31, a multiple quantum well layer 32, and a p-type contact layer 33 are sequentially formed on the n-type tunnel junction layer 41. . Then, electrodes 34 and 35 for mesa processing and refractive index control and electrodes 15 and 17 for laser diode are formed. Of course, the upper electrode 15 is formed on the contact layer 43.

Next, the operation of the surface emitting laser shown in FIG. 3 will be described. Differences from FIG. 1 will be mainly described.
When a voltage is applied between the upper electrode 15 and the lower electrode 17, the tunnel junction layer 41 in the central portion of the low resistance portion avoiding the ion implantation region 44 from the upper electrode 15 through the contact layer 43 and the spacer layer 42. Current (electrons) flows to the tunnel junction layer 40 and is converted to holes, and current (holes) flows through the upper spacer layer 14 and the active layer 13. Further, current (electrons) flows through the active layer 13, the lower spacer layer 12, the lower DBR layer 11, and the substrate 10 to the lower electrode 17.

  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 above-described optical resonator and is extracted from the outlet of the substrate 10 (that is, the back surface of the substrate 10). It is emitted as laser light.

  The film thicknesses of the upper spacer layer 14 and the lower spacer layer 12 are adjusted so that the antinodes of the standing wave come to the active layer 13 and the nodes of the standing wave come to the tunnel junction part. Further, the film thicknesses of the spacer layer 42, the contact layer 43, and the contact layers 31 and 33 of the refractive index control unit 30 are adjusted so that the boundary between the air gap AG and the multiple quantum well layer 32 have antinodes of standing waves. Is done. That is, the phase of the laser beam is adjusted by the film thicknesses of the upper spacer layer 14, the lower spacer layer 12, the spacer layer 42, the contact layer 43, and the contact layers 31 and 33 of the refractive index control unit 30.

  The operation of changing the oscillation wavelength by the dielectric multilayer mirror 16 and the refractive index controller 30 is the same as that of the surface emitting laser shown in FIG.

  In this way, the dielectric multilayer mirror 16 moves in the vertical direction to greatly change the oscillation wavelength over a wide wavelength range. In addition, the refractive index control unit 30 changes the oscillation wavelength at high speed independently of the change of the oscillation wavelength by the dielectric multilayer mirror 16. Further, the refractive index control unit 30 reduces oscillation wavelength fluctuations caused by the vertical movement of the dielectric multilayer mirror 16. Thereby, the oscillation wavelength can be changed at high speed (for example, several [μs]) over a wide wavelength range.

  Further, since the refractive index control unit 30 is monolithically integrated, it can be produced at a low cost.

[Third embodiment]
Next, a wavelength tunable surface emitting laser device using the surface emitting laser shown in FIG. 1 or 3 will be described. FIG. 4 is a block diagram showing a third embodiment (wavelength tunable surface emitting laser device) of the present invention. Here, the same components as those in FIGS. 1 to 3 are denoted by the same reference numerals, and description thereof is omitted. In FIG. 4, a surface emitting laser 100 is the surface emitting laser shown in FIG.

  An oscillation wavelength fine adjustment circuit (hereinafter abbreviated as a fine adjustment circuit) 50 includes a light receiving means 51 and a drive means 52 for the refractive index control unit 30 and constitutes a feedback circuit. Then, the fine adjustment circuit 50 receives a part of the laser light emitted from the surface emitting laser 100 as the output light of the apparatus, and sets the refractive index of the refractive index control unit 30 based on the wavelength of the received laser light. Control. The light receiving means 51 is, for example, a spectroscope, and receives part of the laser light emitted from the surface emitting laser 100 and measures the oscillation wavelength of the laser light. The driving unit 52 controls the refractive index of the refractive index control unit 30 based on the measurement result of the light receiving unit 51.

  An oscillation wavelength coarse adjustment circuit (hereinafter, abbreviated as a coarse adjustment circuit) 60 has a memory 61 and a drive means 62 for driving the MEMS, and moves the membrane 18 and the dielectric multilayer mirror 16 up and down. The memory 61 stores data related to the voltage applied to change the oscillation wavelength. The driving means 62 applies a voltage to the MEMS according to the data in the memory 61 to move the membrane 18 and the dielectric multilayer mirror 16 in the vertical direction.

The operation of such an apparatus will be described.
The change of the oscillation wavelength is set from the wavelength λ0 to the wavelength λ1 from a setting unit (not shown). As a result, the driving means 62 reads out data for changing the oscillation wavelength from the wavelength λ 0 to the wavelength λ 1 from the memory 61. Note that the memory 61 stores, as data, the value of voltage application that causes the hunting that occurs when the membrane 18 and the dielectric multilayer mirror 16 are moved in the vertical direction to change the oscillation wavelength within the wavelength range λ2. Has been. The data in the memory 61 may be measured in advance at the time of manufacturing or maintenance of the apparatus and stored in the memory 61.

  Then, the dielectric multilayer mirror 16 is moved up and down by the driving means 62 and the oscillation wavelength is changed. The light receiving means 51 measures the wavelength of the laser light emitted from the surface emitting laser 100. Further, the driving unit 52 obtains an error between the wavelength of the measurement result and the wavelength λ1 set by the setting unit (not shown), and applies a voltage to the electrodes 34 and 35 of the refractive index control unit 30 based on the error. , Reduce or eliminate the wavelength error.

  As described above, the coarse adjustment circuit 60 moves the dielectric multilayer mirror 16 of the surface emitting laser 100 in the vertical direction to greatly change the oscillation wavelength over a wide wavelength range. In addition, the fine adjustment circuit 50 changes the refractive index of the refractive index control unit 30 based on the wavelength of the laser light from the surface emitting laser 100, and the oscillation wavelength generated by the vertical movement of the dielectric multilayer mirror 16 Reduce or reduce variation. Thereby, the oscillation wavelength can be changed at high speed over a wide wavelength range.

In addition, this invention is not limited to this, The following may be sufficient.
The refractive index control unit 30 of the surface emitting laser shown in FIGS. 1 and 3 is provided with a multiple quantum well layer 32 in the refractive index control layer, and changes the effective optical path length of the optical resonator by the quantum confined Stark effect. Although the configuration in which the wavelength is changed is shown, any refractive index control unit 30 may be used as long as it has a refractive index control layer whose refractive index is changed by voltage or current. For example, the following may be used.

(1) The refractive index control unit 30 has a pin structure in the refractive index control layer and the upper and lower layers, and controls the electric field or carrier density in the i region by applying a voltage or flowing a current to the electrodes 34 and 35, and refracting. You may change the refractive index of a rate control layer (for example, Unexamined-Japanese-Patent No. 5-63301, paragraph number 0007-0008).

(2) The refractive index control unit 30 uses the refractive index control layer as a p-type semiconductor layer and the upper electrode 34 as a Schottky electrode. Then, the refractive index control layer and the Schottky electrode may be joined to form a semiconductor-metal Schottky junction. When a voltage is applied to the Schottky electrode, a depletion layer spreads on the p-type semiconductor layer side. As a result, the carrier distribution changes and the refractive index changes (for example, JP-A-8-204280, paragraphs 0021-0023, FIG. 1-2).

(3) The refractive index control unit 30 uses the refractive index control layer as a p-type semiconductor layer. In addition, an electrode having a MIS (Metal Insulator Semiconductor) structure made of an insulating film (for example, SiO 2 film) and a metal (for example, Au) is provided on the refractive index control layer. When a voltage is applied to the MIS structure electrode, a depletion layer spreads on the p-type semiconductor layer side. As a result, the carrier distribution changes and the refractive index changes (for example, JP-A-8-204280, paragraph numbers 0024-0030, FIG. 3-4). Note that the insulator film is preferably made of a material with little light absorption, or made as thin as possible so as to reduce light absorption.

(4) A material having a piezoelectric effect is used for the refractive index control layer. Then, by applying a voltage to the electrodes 34 and 35, the refractive index of the refractive index control layer may be changed by the photoelastic effect. (For example, Japanese Patent Publication No. 8-8375, page 2-3, FIG. 1-2).

  Further, in the surface emitting laser shown in FIGS. 1 and 3, the structure in which the upper electrode 34 and the lower electrode 35 for controlling the refractive index are provided separately from the upper electrode 15 and the lower electrode 17 for the laser diode is shown. The upper electrode 15 for the laser diode and the lower electrode 35 for refractive index control may be set to a common potential. Alternatively, only one of the electrode 15 and the electrode 35 may be provided and shared without providing the separation layer 19.

  In the surface emitting laser shown in FIGS. 1 and 3, the laser light is emitted downward from the extraction port of the substrate 10 (that is, the back surface of the substrate 10). It may be provided and emitted upward. At this time, the substrate 10 and the lower electrode 17 do not need to be provided with an extraction port.

  In the surface-emitting laser shown in FIGS. 1 and 3, the case where the oscillation wavelength is changed from the wavelength λ0 to the wavelength λ1 has been described as an example, but the oscillation wavelength may be stabilized. That is, in the surface emitting laser, the mechanically driven dielectric multilayer mirror 16 moves up and down depending on the use environment (for example, vibration, temperature fluctuation, impact, etc.), and the oscillation wavelength fluctuates. Therefore, when the dielectric multilayer mirror 16 moves in the vertical direction depending on the usage environment, the refractive index control unit 30 may reduce the oscillation wavelength fluctuation.

  As described above, even if the dielectric multilayer mirror 16 moves in the vertical direction due to the influence of the use environment, the refractive index control unit 30 oscillates at high speed independently of the change of the oscillation wavelength by the dielectric multilayer mirror 16. The wavelength is changed, and the refractive index control unit 30 reduces oscillation wavelength fluctuations caused by the vertical movement of the dielectric multilayer mirror 16, so that laser light with a stable wavelength can be emitted.

  In the surface emitting laser shown in FIGS. 1 and 3, when the oscillation wavelength is changed from the wavelength λ0 to the wavelength λ1, the dielectric multilayer mirror 16 is moved in the vertical direction and the refractive index of the refractive index control unit 30 is changed. The configuration is shown in which the oscillation wavelength of the laser light output from the surface emitting laser is changed, but when the wavelength difference between the wavelength λ0 and the wavelength λ1 is small (for example, the wavelength difference is equal to or less than the wavelength range λ2), the dielectric The oscillation wavelength may be changed at high speed only by the refractive index control unit 30 without moving the body multilayer mirror 16.

  In the surface emitting laser shown in FIGS. 1 and 3, the membrane 18 is provided in parallel with the substrate 10. However, the membrane 18 may be a convex surface or a concave surface. That is, the shape of the dielectric multilayer mirror 16 is convex or concave. Thereby, the transverse mode of the laser beam can be selected.

  In the surface emitting laser shown in FIGS. 1 and 3, the refractive index control unit 30 is placed on the surface of the compound semiconductor (the upper surface of the upper spacer layer 14 in FIG. 1 and the upper surface of the contact layer 43 in FIG. 3) through the separation layer 19. Although the monolithically integrated configuration is shown, the refractive index control unit 30 is formed as a separate chip from each of the compound semiconductor and the MEMS, and is bonded to the surface of the compound semiconductor or the dielectric multilayer mirror 16 with solder or an adhesive. Also good. The separation layer 19 is not necessarily provided if it is electrically insulated by the bonding material. Further, the refractive index control unit 30 may be provided in the air gap AG so as not to contact the compound semiconductor surface or the dielectric multilayer mirror 16.

  In this way, the refractive index control unit 30 is not monolithically integrated on the compound semiconductor surface, but is created and bonded as a separate chip, so there is no need to consider lattice matching with the compound semiconductor surface. As a result, the range of selection of materials is widened, and the refractive index control unit 30 can be formed of an optimal material.

  Further, in the wavelength tunable surface emitting laser device shown in FIG. 4, the case where the oscillation wavelength of the surface emitting laser 100 is changed from the wavelength λ0 to the wavelength λ1 by the fine adjustment circuit 50 and the coarse adjustment circuit 60 has been described as an example. The oscillation wavelength of laser light emitted from the light emitting laser 100 may be stabilized. That is, in the surface emitting laser 100, the mechanically driven dielectric multilayer mirror 16 moves up and down depending on the use environment, and the oscillation wavelength varies. Therefore, when the dielectric multilayer mirror 16 moves in the vertical direction depending on the usage environment, the fine adjustment circuit 50 detects an error due to wavelength fluctuation and controls the refractive index control unit 30 to reduce or reduce the oscillation wavelength fluctuation to zero. Good.

  As described above, even if the dielectric multilayer mirror 16 moves in the vertical direction due to the influence of the use environment, the fine adjustment circuit 50 determines the refractive index of the refractive index control unit 20 based on the wavelength of the laser light from the surface emitting laser. To change. As a result, fluctuations in the oscillation wavelength caused by the vertical movement of the dielectric multilayer mirror 16 are reduced, so that laser light with a stable wavelength can be emitted.

1 is a structural cross-sectional view showing a first embodiment of the present invention. It is the figure which showed the characteristic at the time of changing the oscillation wavelength of the surface emitting laser shown in FIG. It is the composition sectional view showing the 2nd example of the present invention. It is the structure sectional view which showed the 3rd Example of this invention. It is the structure sectional view which showed an example of the conventional surface emitting laser. It is the structure sectional drawing which showed the other example of the conventional surface emitting laser. It is the figure which showed the characteristic at the time of changing the oscillation wavelength of the surface emitting laser shown in FIG.

Explanation of symbols

10 Semiconductor substrate 11 Lower DBR layer (lower distributed reflection layer)
13 Active layer 16 Dielectric multilayer mirror (Upper distributed reflection layer)
30 Refractive Index Control Unit 32 Multiple Quantum Well Layer (Refractive Index Control Layer)
50 Oscillation wavelength fine adjustment circuit 60 Oscillation wavelength coarse adjustment circuit 100 Surface emitting laser AG Air gap

Claims (11)

A lower distributed reflective layer is provided between the semiconductor substrate and the active layer, an upper distributed reflective layer is provided above the active layer via an air gap, and an optical resonator is formed by the upper distributed reflective layer and the lower distributed reflective layer. A surface emitting laser that emits laser light in a direction perpendicular to the semiconductor substrate,
A refractive index control unit having a refractive index control layer provided inside the optical resonator and having a refractive index that changes,
The surface-emitting laser, wherein the upper distributed reflection layer is formed by a semiconductor microfabrication technique and is movable in the vertical direction.   The surface emitting laser according to claim 1, wherein the refractive index control unit is provided in contact with the air gap.   3. The surface emitting laser according to claim 1, wherein the refractive index control unit is monolithically integrated on the surface of the compound semiconductor having at least the active layer and the lower distributed reflection layer.   The refractive index control unit is formed in a separate chip from each of the compound semiconductor having at least the active layer and the lower distributed reflective layer and the upper distributed reflective layer, and is bonded to the surface of the compound semiconductor or the upper distributed reflective layer. The surface emitting laser according to claim 1 or 2, wherein   The surface emitting laser according to claim 1, wherein the refractive index control layer of the refractive index control unit is a semiconductor junction layer whose refractive index changes by current injection or voltage application. The refractive index control unit has a Schottky electrode,
The refractive index control layer of the refractive index control unit is bonded to the Schottky electrode to form a semiconductor-metal Schottky junction, and the refractive index is changed by voltage application. A surface emitting laser according to claim 1. The refractive index control unit has a MIS structure electrode composed of an insulator and a metal,
5. The surface emitting laser according to claim 1, wherein a refractive index control layer of the refractive index control unit is bonded to the MIS structure electrode, and changes a refractive index when a voltage is applied.   The surface emitting laser according to claim 1, wherein the refractive index control unit reduces oscillation wavelength fluctuations caused by movement of the upper distributed reflection layer in the vertical direction. A surface emitting laser according to any one of claims 1 to 8,
An oscillation wavelength fine adjustment circuit that changes the oscillation wavelength of the surface emitting laser by controlling the refractive index of the refractive index control unit of the surface emitting laser according to the wavelength of the laser light from the surface emitting laser,
An oscillation wavelength rough adjustment circuit that changes an oscillation wavelength of the surface emitting laser by controlling a vertical position of the upper distributed reflection layer of the surface emitting laser, and the oscillation wavelength fine tuning circuit includes the upper distributed reflection A wavelength tunable surface emitting laser device that reduces oscillation wavelength fluctuations caused by the vertical movement of a layer. In the surface-emitting laser oscillation wavelength control method according to any one of claims 1 to 8,
The upper distributed reflection layer of the surface emitting laser is moved up and down to change the interval between the optical resonators to change the oscillation wavelength, and the refractive index of the refractive index control unit of the surface emitting laser is changed to change the optical resonator. A method for controlling an oscillation wavelength of a surface emitting laser, wherein the oscillation wavelength is changed by changing an effective optical path length. In the surface-emitting laser oscillation wavelength control method according to any one of claims 1 to 8,
The oscillation wavelength coarse adjustment circuit changes the oscillation wavelength by moving the upper distributed reflection layer of the surface emitting laser in the vertical direction to change the interval between the optical resonators,
The oscillation wavelength fine adjustment circuit changes the effective optical path length of the optical resonator by changing the refractive index of the refractive index control unit of the surface emitting laser according to the wavelength of the laser light from the surface emitting laser, An oscillation wavelength control method for a surface emitting laser, characterized in that fluctuations in oscillation wavelength caused by movement of the distributed reflection layer in the vertical direction are reduced.

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