JP2007242667A - Wavelength conversion laser device and multiple wavelength laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small wavelength conversion laser device in which the wavelength can be stabilized by sustaining a constant oscillation wavelength, even if the operating environment such as temperature changes without providing a mechanically movable portion. <P>SOLUTION: The wavelength conversion laser device comprises a surface emission laser element 22 provided with a distributed Bragg reflector (DBR) on one surface thereof and emitting a first laser beam; a wavelength selection filter 24 passing the first laser beam; a nonlinear optical element 26 for converting the first laser beam into a second laser beam of harmonics; a liquid crystal cell 30 having liquid crystal 58 filling the gap between transparent electrodes 54a and 54b, and a reflector of dielectric multilayer film forming an optical resonator together with the distributed Bragg reflector 46 on one surface for changing the refractive index with a voltage applied to the liquid crystal; and a liquid crystal cell control circuit 32 for controlling an electric field applied to the liquid crystal cell, in order to change the wavelength of a laser beam of harmonics which resonates in the optical resonator. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wavelength conversion laser device and a multiwavelength laser device using a surface emitting laser element.

  In recent years, there has been a demand for a wavelength conversion laser device capable of oscillating a laser beam having an arbitrary wavelength in the visible region in an optical disk device or a display device. In addition, research on surface-emitting laser elements as a key device for optical interconnection and parallel optical links has been actively conducted, and in this field, a multi-wavelength laser device capable of changing the output wavelength of laser light is required. .

  A schematic configuration of a conventional general wavelength conversion laser apparatus is shown in FIG. 13, on the optical axis of the semiconductor laser element 2, an input-side collimating lens 4, a nonlinear optical element that generates harmonic light of the fundamental wave of the laser light. 6, an output-side collimating lens 8, a wavelength selection prism 10, and a rotatable diffraction grating mirror 12 are sequentially arranged along the optical axis. Then, by rotating the diffraction mirror 12, the wavelength of the semiconductor laser element 2 is set at a wavelength determined by the oscillation wavelength of the laser light oscillated by the semiconductor laser element 2 itself and between the semiconductor laser element 2 and the diffraction grating mirror 12. The wavelength is stabilized by selecting and controlling the rotation of the diffraction grating mirror 12.

Patent Document 1 discloses a structure in which a movable mirror in the form of a micromachine having a dielectric multilayer mirror is mechanically moved in order to make the wavelength of the surface emitting laser element variable.
Further, Non-Patent Document 1 proposes a wavelength tunable laser device having a structure in which a semiconductor structure that electrically changes a refractive index is provided on a surface emitting laser element.

In addition, as shown in FIG. 14, the conventional multi-wavelength laser device continuously increases the thickness of the SiO ₂ film or the semiconductor thin film on the semiconductor substrate 14 by epitaxial crystal growth using selective growth. The variable thickness layer 17 is provided (see FIG. 14B), and the variable thickness layer 17 is appropriately sliced to form a plurality of laser pixels having different thicknesses (FIG. 14C). The laser light having different wavelengths λ1, λ2, and λ3 can be generated from each laser pixel.

Japanese Patent Laid-Open No. 10-27943 Surface emitting laser “Integration of wavelength control elements” (Kenichi Iga and Fumio Koyama, pp. 234-237, Ohm Corporation 1990)

By the way, in the above-mentioned laser device of Patent Document 1, since a mechanically moving part in the form of a micromachine is necessary to make the wavelength variable, it is necessary to manufacture a movable structure on such a semiconductor substrate. A very complex process must be performed.
In addition, the device example proposed in Non-Patent Document 1 has the advantage that there is no moving part, but because it is a structure that electrically changes the refractive index, light absorption occurs in the semiconductor structure. There was a problem that optical loss was large.

Further, the device example proposed in Non-Patent Document 2 has a problem that the wavelength of laser light oscillated from each laser pixel is determined at the time of manufacturing the device, and the wavelength cannot be changed thereafter.
The present invention has been devised to pay attention to the above problems and to effectively solve them.

A first object of the present invention is to provide a compact wavelength conversion laser device capable of stabilizing the oscillation wavelength by maintaining a constant oscillation wavelength even when the usage environment such as temperature changes without providing a mechanical movable part. It is to provide.
A second object of the present invention is to provide a multi-wavelength laser device capable of outputting laser light having an arbitrary desired wavelength without providing a mechanically movable part, and without forming a multi-wavelength structure for producing a surface emitting laser element. Is to provide.

  The invention according to claim 1 is the wavelength conversion laser device, wherein the first laser beam having the first wavelength is emitted from one surface side to the outside, and the first laser beam from the one surface side is emitted to the other surface side. A surface-emitting laser element having a first reflective film that reflects, a wavelength selection filter, a nonlinear optical element, and a liquid crystal cell in this order in the emission direction of the first laser light, the wavelength filter, The nonlinear optical element transmits a part of the first laser beam that has passed through the wavelength selection filter, a wavelength corresponding to the first wavelength. And converted into a second laser beam having a second wavelength that is different from the first wavelength, and the liquid crystal cell is connected to the first transparent substrate in the emission direction of the first laser beam. The second transparent substrate is disposed with a gap from the second transparent substrate. A transparent substrate in this order, and the first transparent substrate has a first transparent electrode on a side opposite to a side on which the first laser light and the second laser light transmitted through the nonlinear optical element are incident. The gap is filled with liquid crystal, and the second transparent substrate has a second transparent electrode on a side on which the first laser light and the second laser light transmitted through the liquid crystal are incident. A second reflective film that reflects the first laser light and transmits the second laser light is disposed in this order, and is electrically connected to the first transparent electrode and the second transparent electrode. The first laser beam resonates between the first reflective film and the second reflective film and is applied to the liquid crystal from the liquid crystal cell control circuit. The liquid crystal cell control circuit adjusts the voltage to control the refractive index of the liquid crystal. Is adjusted to the first wavelength by the second laser beam is a wavelength conversion laser device being characterized in that a configuration which is emitted to the outside through the liquid crystal cell.

  According to a second aspect of the present invention, in the multi-wavelength laser device, the first reflection film that emits laser light having the first wavelength from one surface side to the outside and reflects the laser light from the one surface side to the other surface side A plurality of laser pixels each having a wavelength selection liquid crystal cell and a wavelength tunable liquid crystal cell in this order in the emission direction of the laser light, and the wavelength selection liquid crystal cell, A first transparent substrate and a second transparent substrate arranged with a gap between the first transparent substrate and a first transparent substrate in this order in the laser light emitting direction, the first transparent substrate, A first transparent electrode is provided on a side opposite to a side on which the laser light emitted from the surface emitting laser element is incident, the gap is filled with liquid crystal, and the second transparent substrate transmits the liquid crystal. The second transparent electrode is provided on the side on which the laser beam is incident. , A first liquid crystal cell control circuit electrically connected to the first transparent electrode and the second transparent electrode, wherein the wavelength-variable liquid crystal cell is third in the laser beam emission direction. A transparent substrate and a second transparent substrate arranged in this order with a gap between the third transparent substrate and the third transparent substrate, the laser transmitting the wavelength selection liquid crystal cell. A third transparent electrode is provided on the side opposite to the light incident side, the gap is filled with liquid crystal, and the fourth transparent substrate is formed on the side on which the laser light transmitted through the liquid crystal is incident. 4 transparent electrodes and a second reflective film that reflects a part of the laser beam are arranged in this order, and are electrically connected to the third transparent electrode and the fourth transparent electrode. A liquid crystal cell control circuit, and for each laser pixel, each laser beam is reflected by the first reflection. And the second reflective film respectively, and the second liquid crystal cell control circuit adjusts the voltage applied to the second liquid crystal to individually adjust the refractive indexes of the second liquid crystals. The first wavelength is set to a predetermined wavelength by controlling each of the first and second laser beams to the predetermined wavelength by the first liquid crystal cell control circuit for each laser pixel. The selected laser light is selected by adjusting the voltage applied to the liquid crystal and individually controlling the refractive index of each first liquid crystal, and the selected laser light is transmitted through the wavelength variable liquid crystal cell and emitted to the outside. The multi-wavelength laser device is characterized in that it is configured as described above.

According to the wavelength conversion laser device of the present invention, a small wavelength capable of stabilizing the oscillation wavelength and maintaining the oscillation wavelength constant even when the usage environment such as temperature changes without providing a mechanical movable part. A conversion laser device can be provided.
Further, according to the multi-wavelength laser device of the present invention, it is possible to output laser light having an arbitrary desired wavelength without providing a mechanically movable part and without forming a multi-wavelength structure for producing a surface emitting laser element. A multi-wavelength laser device capable of being provided can be provided.

In the following, one embodiment of a wavelength conversion laser device and a multi-wavelength laser device according to the present invention will be described in detail with reference to the accompanying drawings.
<First invention>
1 is a sectional view showing a wavelength conversion laser device according to the first invention, FIG. 2 is an enlarged sectional view showing a surface emitting laser element according to the first invention, and FIG. 3 is an enlarged sectional view showing a liquid crystal cell according to the first invention. FIG. 4 is an operation explanatory diagram for explaining the operation of the liquid crystal cell in the first invention, and FIG. 5 is a diagram showing the principle of selecting the wavelength of the laser beam by the wavelength selection filter in the first invention.

As shown in FIG. 1, the wavelength conversion laser device 20 includes a surface emitting laser element 22 that generates a laser beam (first laser beam) serving as a fundamental wave, a wavelength selection filter 24, a nonlinear optical element 26, The antireflective film 28 and the liquid crystal cell 30 are sequentially joined, and the liquid crystal cell 30 is connected to and controlled by the liquid crystal cell control circuit 32. The surface emitting laser element 22 is driven by a surface emitting laser driver 33.
Specifically, the entire wavelength conversion laser device 20 is provided on a circuit board 34, and the surface-emitting laser element 22 is closely fixed on the circuit board 34 by a pedestal 36.

  First, the surface emitting laser element 22 will be described. The structure of the surface emitting laser element 22 is shown in FIG. The surface-emitting laser element 22 shown here is a substrate surface emitting type, and is a conductive layer 40, an active layer 42, a spacer layer 44, and a first reflective film on the semiconductor substrate 38 (lower side in FIG. 2). A semiconductor DBR (Distributed Bragg Reflector) reflective multilayer film 46, a first electrode 48, and a second electrode 50 as a Bragg reflector are formed to constitute the whole. Note that in this type of surface emitting laser element 22, a substrate made of a material in which the semiconductor substrate 38 is transparent with respect to the oscillation wavelength of the active layer 42 is selected.

As a specific example, a semiconductor substrate 38 is u-GaAs, an n-type conductive layer 40 is n-GaAs, an active layer 42 is an InGaAs / GaAs MQW (for example, wavelength: 940 nm), and a spacer layer 44 is formed. The u-Al _0.6 Ga _0.4 As, the semiconductor DBR reflective multilayer film 46 is a p- (AlAs / GaAs) multilayer film (reflectance 99.9% or more), and the first electrode 48 is a p-type ohmic electrode (AuZnNi Etc.), and the second electrode 50 can be composed of an n-type ohmic electrode (AuGeNi or the like). In addition, materials used for semiconductor lasers, such as InP-based materials used for long wavelength semiconductor lasers, can also be applied.
The manufacturing procedure of the surface emitting laser element 22 is the same as the manufacturing procedure of the surface emitting laser element that is generally widely used, and thus the description thereof is omitted.

Next, the wavelength selection filter 24 is formed by alternately laminating dielectric multilayer films, for example, SiO ₂ films and TiO ₂ films. The structure of the dielectric multilayer film is designed in accordance with the wavelength specification of the nonlinear optical element 26 used in this apparatus. That is, the wavelength selection filter 24 is configured to be non-reflective only for the wavelength specification wavelength of the nonlinear optical element 26 and reflect the harmonic laser beam (second laser beam) generated by the nonlinear optical element 26. Designed.

Next, the nonlinear optical element 26 will be described with reference to FIG. This non-linear optical element 26 is an element (PPRN) that has undergone polarization inversion processing so as to be quasi-phase matched with LiNbO ₃ , LiTaO _3, etc., which are optical crystals having non-linear optical characteristics such as KTiOPO ₄ , LiNbO ₃ , LiTaO _3, etc. [Periodically Poled LN], called PPLT). The nonlinear optical element 26 converts the wavelength of the laser light generated by the surface-emitting laser element 22 into harmonic light (higher order) laser light. For example, when the nonlinear optical element 26 has second-order nonlinearity, the fundamental wave having a wavelength of 940 nm is converted into a second-order harmonic having a wavelength of 470 nm.
The non-reflective layer 28 is designed so that the fundamental laser beam is not reflected with respect to the harmonic laser beam. The non-reflective layer 28 has the purpose of preventing an extra reflection point between the liquid crystal cell 30 and the nonlinear optical element 26. In some cases, the non-reflective layer 28 may be omitted.

Next, the configuration of the liquid crystal cell 30 will be described. The configuration of the liquid crystal cell 30 is shown in FIG. The liquid crystal cell 30 includes a lower glass substrate 52a that is a first transparent substrate and an upper glass substrate 52b that is a second transparent substrate. One surface of the lower glass substrate 52a is connected to the non-reflective layer 28 side, and a lower transparent electrode (first transparent electrode) 54a made of, for example, ITO is formed on the other surface.
A reflecting mirror (second reflecting film) 56 made of a dielectric multilayer film is formed on one surface of the upper glass substrate 52b. This dielectric multilayer film is formed by, for example, alternately laminating SiO ₂ films 56a and TiO ₂ films 56b. This dielectric multilayer film passes the wavelength of the specification of the nonlinear optical element 26 and reflects the fundamental wave of the surface emitting laser element 22. On the surface of the reflecting mirror 56, an upper transparent electrode (second transparent electrode) 54b made of, for example, ITO is formed.

The lower glass substrate 52a and the upper glass substrate 52b are bonded so that the lower transparent electrode 54a and the upper transparent electrode 54b face each other, and the liquid crystal 58 is sealed therebetween. This sealing is performed by interposing a spacer-mixed adhesive 59 around the transparent electrodes 54a and 54b.
The liquid crystal molecules 58a in the liquid crystal 58 are aligned in a horizontal or vertical direction or an intermediate inclination with respect to the surface of the lower glass substrate 52a. For alignment of the liquid crystal molecules 58a, for example, alignment films (not shown) are provided on the sides of the transparent electrodes 54a and 54b that are in contact with the liquid crystal 58, respectively.

  Here, the operation of the liquid crystal cell 30 will be described. FIG. 4 shows the operation of the liquid crystal cell 30. FIG. 4 schematically shows the liquid crystal cell 30. First, as described above, the liquid crystal molecules 58a are aligned so as to have a horizontal, vertical, or intermediate inclination with respect to the surfaces of the glass substrates 52a and 52b (see FIG. 3). When a voltage is applied to the lower transparent electrode 54a and the upper transparent electrode 54b sandwiching the liquid crystal 58, the alignment direction of the liquid crystal molecules 58a can be changed. Since the liquid crystal 58 has refractive index anisotropy in the direction of the liquid crystal molecules 58a, the refractive index in the liquid crystal 58 is changed by changing the orientation of the liquid crystal molecules 58a. Therefore, since the alignment condition of the liquid crystal molecules 58a can be adjusted by the voltage applied between the lower transparent electrode 54a and the upper transparent electrode 54b, the refractive index can be controlled by the voltage applied thereto. In general, the refractive index of liquid crystal changes by about 0.2.

Next, the operation of the wavelength conversion laser device 20 of the first invention configured as described above will be described.
First, the surface emitting laser element 22 is driven by a laser driver 33, and the liquid crystal cell 30 is electrically controlled by a liquid crystal cell control circuit 32. The light generated in the active layer 42 of the surface emitting laser element 22 is transmitted between the semiconductor DBR reflecting multilayer film 46 which is a reflecting mirror of the surface emitting laser element 22 and the reflecting mirror 56 made of a dielectric multilayer film on the liquid crystal cell 30. Then, a resonator structure is formed and laser oscillation is performed (shown as an optical resonator 60 in FIG. 1). In this state, if the voltage applied to the liquid crystal cell 30 is changed, the refractive index in the liquid crystal cell 30 changes, so that the length (optical path length) of the optical resonator 60 changes. Then, since the mode interval in the optical resonator 60 changes, the laser oscillation wavelength also changes. Therefore, the wavelength of the laser beam can be controlled by controlling the voltage applied to the liquid crystal cell 30.

Incidentally, when the thickness of the liquid crystal 58 is 10 μm and the change in the refractive index of the liquid crystal 58 is 0.2, the resonator length can be varied by 2 μm (= 10 μm × 0.2). This variable length can be changed by changing the thickness of the liquid crystal 58 (liquid crystal spacer thickness) or selecting a material having a high refractive index anisotropy.
However, in this state, multimode oscillation occurs (FIG. 5A), and the wavelength conversion efficiency of the nonlinear optical element 26 is not good. For this reason, a wavelength selection filter 24 is provided so that only wavelengths that match the conversion wavelength of the nonlinear optical element 26 can be picked up (FIGS. 5B and 5C). That is, the surface emitting laser element 22 can oscillate laser light having a single wavelength shown in FIG.

  When high-efficiency wavelength conversion is required, it is preferable to use a quasi phase matching nonlinear optical element such as PPLN for the nonlinear optical element 26. However, the quasi phase matching nonlinear optical element such as PPLN has a very narrow wavelength tolerance (about 0.1 nm · cm, and about 0.5 nm if the element length is about 2 mm), so that the wavelength stability of the surface emitting laser element 22 is stabilized. Needs to be made. Therefore, even if the oscillation wavelength of the surface emitting laser element 22 changes due to an environmental change or the like, the resonator length is adjusted by changing the refractive index of the liquid crystal cell 30, thereby adjusting the oscillation wavelength and stabilizing the wavelength. Can be planned. In other words, if the oscillation wavelength of the spectrum of the multimode oscillation shown in FIG. 5A changes due to an environmental change or the like, the wavelength of the laser light extracted by the wavelength selection filter 24 may change or cannot be extracted. However, in such a case, the refractive index is adjusted so as to cancel out the fluctuation of the wavelength in the liquid crystal cell 30, that is, the resonator length is adjusted, and thereby the oscillation wavelength can be stabilized.

<Second invention>
Next, a multiwavelength laser apparatus according to the second aspect of the present invention will be described.
In the first invention, the object is to extract a laser beam having a specific stable wavelength from a wavelength conversion laser device provided with one surface emitting laser element. In the second invention, a plurality of surface emitting devices are used. In a multi-wavelength laser device having a laser element, an object is to oscillate individual surface emitting laser elements at different wavelengths by combining a wavelength variable section and a wavelength selection filter section.

  6 is a cross-sectional perspective view showing a multi-wavelength laser device according to the second invention, FIG. 7 is a top view of the multi-wavelength laser device shown in FIG. 6, and FIG. 8 shows a surface emitting laser element array unit according to the second invention. FIG. 9 is an enlarged cross-sectional view, FIG. 9 is an enlarged cross-sectional view showing one wavelength selection liquid crystal cell constituting the wavelength selection liquid crystal cell unit in the second invention, and FIG. 10 is an operation explanatory view for explaining the operation of the wavelength selection liquid crystal cell. FIG. 11 is an operation explanatory view for explaining the operation of the wavelength tunable liquid crystal cell unit, and FIG. 12 is a principle explanatory view for explaining the principle of selecting laser light of a specific wavelength from multimode oscillation. Here, the same reference numerals are assigned to the same constituent members as those of the first invention shown in FIGS.

  The multi-wavelength laser device 62 includes a surface-emitting laser element array unit 64 in which a plurality of laser pixels Px made of surface-emitting laser elements 22 are arranged in a matrix (array) vertically and horizontally, a non-reflective film 28, an internal A wavelength selection liquid crystal cell unit 68 in which a plurality of wavelength selection liquid crystal cells sealed with liquid crystal are provided in correspondence with the laser pixel Px, and a wavelength variable liquid crystal cell 70 in which liquid crystal is sealed is provided. A plurality of wavelength tunable liquid crystal cell units 72 provided in correspondence with the laser pixels Px, and the wavelength tunable liquid crystal cell units 72 are connected to and controlled by a first control circuit 74; The wavelength selection liquid crystal cell 68 is connected to and controlled by the second control circuit 76. Here, a case where nine laser pixels Px are provided is shown as an example in order to output nine types of laser light having wavelengths λ1 to λ9.

  Specifically, the entire multi-wavelength laser device 62 is provided on the circuit board 34, and the surface-emitting laser element array unit 64 is tightly fixed on the circuit board 34 by a pedestal 36. Here, the surface emitting laser elements 22 themselves oscillate in the same wavelength mode. The surface emitting laser elements 22 can be individually controlled for each laser pixel Px, that is, for each surface emitting laser element 22, by a surface emitting laser driver 33 provided individually.

In the wavelength selection liquid crystal cell unit 68, a plurality of wavelength selection liquid crystal cells 66 provided in correspondence with the laser pixels Px are arranged, and the second control circuit 76 supplies the wavelength selection liquid crystal cells 66. A wiring 78 (see FIG. 7) extends to the liquid crystal cell 66, and each wavelength selection liquid crystal cell 66 can be controlled individually, that is, independently for each laser pixel Px.
The wavelength-tunable liquid crystal cell unit 72 includes a plurality of wavelength-selective liquid crystal cells 70 corresponding to the laser pixels Px. The first control circuit 74 supplies the wavelength-variable liquid crystal cells 70. Wiring 80 (see FIG. 7) is extended to the liquid crystal cell 70, and each wavelength variable liquid crystal cell 70 can be controlled individually, that is, independently for each laser pixel Px.

The surface emitting laser element array unit 64 has a plurality of surface emitting laser elements 22 arranged in an array as described above, and each surface emitting laser element 22 basically has the structure of the first invention. It is constituted similarly. However, the material which comprises each layer is changed as follows here.
More specifically, as shown in FIG. 8, the semiconductor substrate 38 is u-InP, the conductive layer 40 is n-InP, the active layer 42 is an InGaAsP / InP MQW (for example, wavelength 1550 nm), spacers The layer 44 is u-InP, the semiconductor DBR reflective multilayer film 46 as a distributed Bragg reflector is a p- (InGaAsP / InP) multilayer film (reflectance of 99.9% or more), and the first electrode 48 is a p-type ohmic electrode ( AuZnNi or the like) and the second electrode 50 can be configured by n-type ohmic electrodes (AuGeNi or the like), respectively. In addition, materials used for other semiconductor lasers such as GaAs-based and InGaAs-based materials used for short wavelength semiconductor lasers can also be applied. The manufacturing procedure of each surface emitting laser element 22 is the same as the manufacturing procedure of a surface emitting laser that is generally widely used, and thus the description thereof is omitted.

Next, the operation of the variable wavelength selection liquid crystal cell 66 will be described. Here, since each wavelength selection liquid crystal cell 66 constituting the wavelength selection liquid crystal cell unit 68 has the same structure, one wavelength selection liquid crystal cell 66 is taken out and described with reference to FIG.
The wavelength selecting liquid crystal cell 66 has a lower glass substrate (first transparent substrate) 82a and an upper glass substrate (second transparent substrate) 82b. One surface of the lower glass substrate 82a is connected to the non-reflective 28 side. A reflecting mirror 84 made of a dielectric multilayer film is formed on the other surface of the lower glass substrate 82a. This dielectric multilayer film is formed by, for example, alternately laminating SiO ₂ films 84a and TiO ₂ films 84b. A lower transparent electrode (first transparent electrode) 88a made of, for example, ITO is formed on the surface of the reflecting mirror 84.

A reflecting mirror 90 made of a dielectric multilayer film is formed on one surface of the upper glass substrate 82b. This dielectric multilayer film is formed by, for example, alternately laminating SiO ₂ films 90a and TiO ₂ films 90b. An upper surface transparent electrode (second transparent electrode) 88b made of, for example, ITO is formed on the surface of the reflecting mirror 90.
The lower glass substrate 82a and the upper glass substrate 82b are bonded so that the lower transparent electrode 88a and the upper transparent electrode 88b face each other, and the liquid crystal 92 is sealed therebetween. This sealing is performed by interposing a spacer mixed adhesive 94 around the transparent electrodes 88a and 88b.

The liquid crystal 92 is aligned in the horizontal or vertical direction or an intermediate inclination with respect to the surface of the lower glass substrate 82a. For alignment of the liquid crystal 92, for example, an alignment film (not shown) is provided on each of the transparent electrodes 88a and 88b on the side in contact with the liquid crystal.
Here, as shown in FIG. 6, the reflecting mirrors 84 and 90 including both the lower and upper glass substrates 82 a and 82 b are formed in common with respect to the wavelength selection liquid crystal cells 66.

  Next, the operation of the wavelength selecting liquid crystal cell 66 will be described. An explanatory diagram of this operation is shown in FIG. The wavelength selection liquid crystal cell 66 functions as a wavelength selection filter that transmits only laser light of an arbitrary wavelength. As described above, the lower glass substrate 82a and the upper glass substrate 82b are each made of a dielectric multilayer film. There are reflecting mirrors 84 and 90, and a liquid crystal 92 is sealed between them. When the refractive index of the liquid crystal 92 is changed by controlling the electric field applied to the liquid crystal 92 based on the above principle, the same effect as the etalon is generated, and only laser light having a wavelength corresponding to the optical gap of the liquid crystal 92 can be transmitted. It becomes like this. That is, as shown in FIG. 10, when the applied voltage is controlled, the filter characteristics change, and the wavelength of the laser light that passes through the filter characteristics changes between λ1 and λ3, for example. Therefore, if the voltage applied to the wavelength selection liquid crystal cell 66 is controlled, it operates as a wavelength selection filter that transmits only laser light of an arbitrary wavelength as described above.

  The configuration of each wavelength variable liquid crystal cell 70 in the wavelength variable liquid crystal cell unit 72 is exactly the same as the liquid crystal cell 70 (see FIG. 3) and the operation principle (see FIG. 4) of the first invention. The description is omitted. Here again, the reflecting mirror (second reflecting film) 56 including the glass substrates (first and second transparent substrates) 52 a and 52 b on the lower surface and the upper surface is formed in common with respect to each wavelength variable liquid crystal cell 70. .

Next, the operation of the multiwavelength laser device 62 of the second invention configured as described above will be described.
The operation waveforms at this time are shown in FIGS. Each surface emitting laser element 22 of the surface emitting laser element array unit 64 is driven independently for each laser pixel Px by each surface emitting laser driver 33. Each wavelength selection liquid crystal cell 66 of the wavelength selection liquid crystal cell unit 68 is controlled for each cell by the second control circuit 76. Similarly, each wavelength variable cell 70 of the wavelength variable liquid crystal cell unit 72 is controlled by the first control circuit 74 for each cell.

  Here, when attention is paid to one laser pixel Px, the light generated in the active layer 42 of the surface emitting laser element 22 is the wavelength tunable of the semiconductor DBR reflective multilayer film 46 which is a reflecting mirror and the wavelength tunable liquid crystal cell unit 72. An optical resonator structure is formed between the reflective film 56 in the liquid crystal cell 70 and the laser light is oscillated. In such a surface emitting laser, the optical resonator structure becomes an external resonator structure, and multimode oscillation occurs. In this state, if the voltage applied to the wavelength tunable liquid crystal cell 70 is changed, the refractive index of the liquid crystal in the wavelength tunable liquid crystal cell 70 is changed, so that the length of the resonator is changed. Then, since the mode interval in the resonator changes, the laser oscillation wavelength also changes. The state at this time is shown in FIG. Therefore, the wavelength of the laser light can be controlled by controlling the voltage applied to the wavelength variable liquid crystal cell 70.

Incidentally, when the thickness of the liquid crystal 58 is 10 μm and the change in the refractive index of the liquid crystal 58 is 0.2, the resonator length can be varied by 2 μm (= 10 μm × 0.2). The variable length can be changed by changing the thickness of the liquid crystal 58 (liquid crystal spacer thickness) or selecting a material having a high refractive index anisotropy.
However, in this state, since the optical resonator has an external resonator structure, it oscillates in a multimode (see FIG. 12A). Therefore, for wavelength selection having the function of a wavelength selection filter. A liquid crystal cell 66 is provided so that only laser light having a target wavelength can be picked up (see FIG. 12C).

As a wavelength tuning procedure, the voltage of the wavelength selection liquid crystal cell 66 is controlled and tuned to a target wavelength, and then the voltage of the wavelength tuning liquid crystal cell 70 is controlled so that the laser light of the selected wavelength passes. Adjust to. If this operation is performed for each laser pixel of the surface emitting laser element array unit 64, laser light having an arbitrary wavelength with different wavelengths can be emitted at an arbitrary position.
The multi-wavelength laser device 62 can be applied to, for example, a multi-wavelength laser light source for communication wavelength division multiplexing (WDM).

It is sectional drawing which shows the wavelength conversion laser apparatus which concerns on 1st invention. It is an expanded sectional view which shows the surface emitting laser element in 1st invention. It is an expanded sectional view which shows the liquid crystal cell in 1st invention. It is operation | movement explanatory drawing explaining operation | movement of the liquid crystal cell in 1st invention. It is a figure for demonstrating the principle which selects the wavelength of a laser beam with the wavelength selection filter in 1st invention. It is a cross-sectional perspective view which shows the multiwavelength laser apparatus based on 2nd invention. FIG. 7 is a top view of the multiwavelength laser device shown in FIG. 6. It is an expanded sectional view which shows the surface emitting laser element array unit in 2nd invention. It is an expanded sectional view which shows one liquid crystal cell for wavelength selection which comprises the liquid crystal cell unit for wavelength selection in 2nd invention. It is operation | movement explanatory drawing explaining operation | movement of the liquid crystal cell for wavelength selection. It is operation | movement explanatory drawing explaining operation | movement of a wavelength variable liquid crystal cell unit. It is a principle explanatory drawing for demonstrating the principle which selects the laser beam of a specific wavelength from multimode oscillation. It is a schematic block diagram which shows the conventional general wavelength conversion laser apparatus. It is a block diagram which shows the conventional multiwavelength laser apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 20 ... Wavelength conversion laser apparatus, 22 ... Surface emitting laser element, 24 ... Wavelength selection filter, 26 ... Nonlinear optical element, 30 ... Liquid crystal cell, 32 ... Liquid crystal cell control circuit, 38 ... Semiconductor substrate, 40 ... Conductive layer, 42 ... Active layer 46... Semiconductor DBR reflective multilayer film (distributed feedback type reflection mirror: first reflective film) 48... First electrode 50... Second electrode 52 a. Lower transparent electrode, 54b ... Upper transparent electrode, 56 ... Reflector (second reflective film), 58 ... Liquid crystal, 62 ... Multi-wavelength laser device, 64 ... Surface emitting laser element array unit, 66 ... Liquid crystal cell for wavelength selection, 68 ... wavelength selection liquid crystal cell unit, 70 ... wavelength variable liquid crystal cell, 72 ... wavelength variable liquid crystal cell unit, 74 ... first control circuit, 76 ... second control circuit, 82a ... bottom glass substrate, 82 ... top glass substrate.

Claims (2)

In the wavelength conversion laser device,
A surface emitting laser element having a first reflecting film that emits a first laser beam having a first wavelength from one surface side to the outside and reflects the first laser light from the one surface side to the other surface side; ,
In the emission direction of the first laser light, a wavelength selection filter, a nonlinear optical element, and a liquid crystal cell are provided in this order,
The wavelength filter transmits laser light having a predetermined range of wavelengths including the first wavelength,
The nonlinear optical element has a second wavelength which is a wavelength corresponding to the first wavelength and a wavelength different from the first wavelength, with a part of the first laser light transmitted through the wavelength selection filter. Converted into a second laser beam having
The liquid crystal cell is
A first transparent substrate in the emission direction of the first laser light, and a second transparent substrate disposed in this order with a gap from the first transparent substrate,
The first transparent substrate has a first transparent electrode on a side opposite to a side on which the first laser light and the second laser light transmitted through the nonlinear optical element are incident,
The gap is filled with liquid crystal,
The second transparent substrate reflects a second transparent electrode on the side on which the first laser light and the second laser light that have passed through the liquid crystal are incident, and the second laser light to reflect the second laser light. And a second reflective film that transmits the laser light of
A liquid crystal cell control circuit electrically connected to the first transparent electrode and the second transparent electrode;
The first laser light resonates between the first reflective film and the second reflective film, and a voltage applied from the liquid crystal cell control circuit to the liquid crystal is adjusted by the liquid crystal cell control circuit. The first wavelength is adjusted by controlling the refractive index of the liquid crystal,
The wavelength conversion laser device, wherein the second laser light is configured to be transmitted through the liquid crystal cell and emitted to the outside. In a multi-wavelength laser device,
A surface emitting laser element having a first reflective film that emits laser light having a first wavelength from one surface side to the outside and reflects the laser light from the one surface side to the other surface side, and an emission direction of the laser light In addition, a plurality of laser pixels provided with a wavelength selection liquid crystal cell and a wavelength variable liquid crystal cell in this order are arranged,
The wavelength selection liquid crystal cell is:
A first transparent substrate, and a second transparent substrate disposed in this order with a gap from the first transparent substrate in the laser light emitting direction,
The first transparent substrate has a first transparent electrode on a side opposite to a side on which the laser light emitted from the surface emitting laser element is incident,
The gap is filled with liquid crystal,
The second transparent substrate has a second transparent electrode on a side on which the laser light transmitted through the liquid crystal is incident,
A first liquid crystal cell control circuit electrically connected to the first transparent electrode and the second transparent electrode;
The wavelength-tunable liquid crystal cell is
A third transparent substrate and a second transparent substrate arranged with a gap with the third transparent substrate in the laser light emitting direction in this order,
The third transparent substrate has a third transparent electrode on the side opposite to the side on which the laser beam transmitted through the wavelength selection liquid crystal cell is incident,
The gap is filled with liquid crystal,
In the fourth transparent substrate, a fourth transparent electrode and a second reflective film that reflects a part of the laser light are arranged in this order on the side on which the laser light transmitted through the liquid crystal is incident.
A second liquid crystal cell control circuit electrically connected to the third transparent electrode and the fourth transparent electrode;
For each laser pixel, each of the laser beams resonates between the first reflective film and the second reflective film, and is transmitted to the second liquid crystal by the second liquid crystal cell control circuit. By adjusting the applied voltage and individually controlling the refractive index of each of the second liquid crystals, the first wavelength is set to a predetermined wavelength,
The laser light having the predetermined wavelength is adjusted for each laser pixel by adjusting the voltage applied to the first liquid crystal by the first liquid crystal cell control circuit, and the refractive index of each first liquid crystal. Are selected by controlling each individually,
The multi-wavelength laser apparatus characterized in that the selected laser beam is transmitted through the wavelength variable liquid crystal cell and emitted to the outside.

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