JP2006235381A - Electromagnetic wave generator and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave generator efficiently generating a high-output electromagnetic wave having a narrow line width in the range of 0.1 to 10 THz, and also to provide a method for manufacturing the same. <P>SOLUTION: A compound semiconductor pseudo phase matching element 100 includes compound semiconductors 101 and 102 having the same composition. The compound semiconductors 101 and 102 are joined together to form a junction body. The junction body, in which the surface perpendicular to the optical axis where spatial symmetry of the crystals of the compound semiconductors 101 and 102 is inversed is made as the junction surface formed by the joining, is an orientation inversion structure having orientation inversion periods antiparallel to each other with respect to the optical axis direction where the spatial symmetry is inversed. The orientation inversion periods are a natural number multiple of π/Δk (ν1 and ν2 are the frequencies of two wavelength incident light, ν3 is the frequency of a generated electromagnetic wave of 0.1-10 THz, n1, n2, and n3 are refractive indexes of a nonlinear material at the frequencies of ν1, ν2, and ν3, c is the light velocity, and Δk=2π/c×(n1×ν1-n2×ν2-n3×ν3)). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus for generating an electromagnetic wave in the range of 0.1 to 10 THz.

  The 0.1-10 THz band electromagnetic wave, which is the boundary region between light and radio waves, has the property of transmitting many substances, and has been applied to identification of chemical substances, moisture detection, non-invasive imaging of living bodies, etc. Development related to these is actively underway.

  Non-Patent Document 1 discloses an electromagnetic wave generator that generates an electromagnetic wave in a range of 0.1 THz to 10 THz. This device uses a bulk crystal of organic compounds and compound semiconductors with high second-order nonlinear effects, and enters the two-wavelength nanosecond pulse lasers generated from the Q-switched pulse laser into the crystal, thereby satisfying the phase matching condition. Below, a pulse is generated by the difference frequency generation effect.

T. Tanabe, K. Suto, J. Nishizawa, T. Kimura, K. Saito “Frequency-tunable high-power terahertz wave generation from GaP” J. Appl. Phys. 93, pp. 4610-4615

However, the apparatus described in Non-Patent Document 1 has the following problems.
That is, in the difference frequency generation using the bulk nonlinear crystal, when a light source having a large line width such as a parametric oscillator is used as the excitation light source, the line width of the output electromagnetic wave is widened. Actually, according to the apparatus described in Non-Patent Document 1, the half width of the spectrum is 400 GHz even though excitation is performed with excitation light having a time width of 10 ns, and the spectrum width of the Fourier transform limit (1 GHz or less) is reached. It is shown that it has spread by about two digits.

  In addition, there is a limit to taking a large phase matching length, so that there is a problem that the efficiency is poor and the output cannot be increased. According to Non-Patent Document 1, the peak power of the output electromagnetic wave is 480 mW with respect to the excitation light of 4 mJ, and it is difficult to say that both efficiency and power are sufficient from a practical standpoint.

  The present invention has been made to solve the above-described problems, and its object is to generate an electromagnetic wave having a narrow line width in a range of 0.1 THz to 10 THz with high efficiency and high output. An object of the present invention is to provide an electromagnetic wave generating device and a manufacturing method thereof.

  In order to solve the above-described problem, the invention according to claim 1 is configured such that when two-wavelength light having a frequency difference set to 0.1 to 10 GHz is incident, 0.1 to 10 THz is generated by the difference frequency generation by the two-wavelength light. In the electromagnetic wave generation device having a quasi-phase matching type wavelength conversion element for generating an electromagnetic wave, the wavelength conversion element is a first material made of a nonlinear material which is the III-V group or II-VI group compound semiconductor having the same composition. A compound semiconductor and a second compound semiconductor are included, and the first and second compound semiconductors are joined to each other to form a joined body, and the joined body is a stacked surface of the first and second compound semiconductors. An optical axis whose spatial symmetry is reversed, where (bonding surface) is a plane perpendicular to the optical axis where the spatial symmetry of the crystals of the first and second compound semiconductors is reversed. In the direction Azimuth reversal structure having azimuth reversal periods antiparallel to each other, ν1 and ν2 are the frequencies of the incident two-wavelength light, ν3 is the frequency of the generated electromagnetic wave of 0.1 to 10 THz, and n1, n2, When n3 is the refractive index of the nonlinear material at frequencies ν1, ν2, and ν3, c is the speed of light, and Δk = 2π / c × (n1, ν1-n2, ν2-n3, ν3), the azimuth inversion period is It is a natural number multiple of π / Δk.

  The invention according to claim 2 is the invention according to claim 1, further comprising a waveguide for the electromagnetic wave of 0.1 to 10 THz, wherein the wavelength conversion element is arranged in the waveguide. .

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the optical system further comprises excitation means for exciting each of the two-wavelength light incident on the wavelength conversion element, and the two-wavelength light is emitted from the excitation means. It is incident on the wavelength conversion element to generate the 0.1 to 10 THz electromagnetic wave, and the generated 0.1 to 10 THz electromagnetic wave is output.

  According to a fourth aspect of the present invention, in the second aspect of the present invention, the waveguide for the electromagnetic wave of 0.1 to 10 THz is based on plasma confinement.

  According to a fifth aspect of the present invention, in the second aspect of the invention, the waveguide for the electromagnetic wave of 0.1 to 10 THz is based on a refractive index confinement.

  A sixth aspect of the invention is characterized in that, in the invention of any one of the first to fifth aspects, the nonlinear material has a zinc blende structure.

  The invention according to claim 7 is the invention according to claim 6, wherein the joint surface is a (110) plane or a crystallographically equivalent plane to the (110) plane, and the crystal axis direction in which the symmetry is reversed is The [111] axis or the [100] axis or a crystal axis direction equivalent to these is characterized.

  The invention according to claim 8 is the invention according to claim 6 or 7, characterized in that the group III-V compound semiconductor contains at least one of GaAs, GaP or InP.

The invention according to claim 9 is the invention according to claim 6 or 7, wherein the group III-V compound semiconductor is at least In _x1 Al _x2 Ga _(1-x1-x2) N _y1 As _y2 P _{(1-y1- y2)} (0 ≦ x1, x2, y1, y2 ≦ 1, x1 + x2 ≦ 1, y1 + y2 ≦ 1).

  The invention according to claim 10 is the invention according to claim 6 or 7, wherein the II-VI group compound semiconductor contains at least one of β-ZnS, ZnSe, or ZnTe.

The invention according to claim 11 is the invention according to claim 6 or 7, wherein the II-VI group compound semiconductor is at least Zn _x1 Cd _x2 Hg _(1-x1-x2) S _y1 Se _y2 Te _{(1-y1- y2)} (0 ≦ x1, x2, y1, y2 ≦ 1, x1 + x2 ≦ 1, y1 + y2 ≦ 1).

  The invention according to claim 12 is the invention according to any one of claims 1 to 5, wherein the nonlinear material has a wurtzite structure.

  The invention according to claim 13 is the crystal according to claim 12, wherein the bonding surface is a (1100) plane, a (1120) plane, or a plane crystallographically equivalent to the plane, and the symmetry is reversed. The axial direction is the [0001] axial direction.

  The invention according to claim 14 is the invention according to claim 12 or 13, characterized in that the group III-V compound semiconductor contains at least GaN.

According to a fifteenth aspect of the present invention, in the invention of the twelfth or thirteenth aspect, the III-V group compound semiconductor is at least In _x1 Al _x2 Ga _(1-x1-x2) N _y1 As _y2 P _{(1-y1- y2)} (0 ≦ x1, x2, y1, y2 ≦ 1, x1 + x2 ≦ 1, y1 + y2 ≦ 1).

  The invention according to claim 16 is the invention according to claim 12 or 13, wherein the II-VI group compound semiconductor contains at least one of α-ZnS, ZnO, CdS, CdSe, or CdTe. To do.

The invention according to claim 17 is the invention according to claim 12 or 13, wherein the II-VI group compound semiconductor is at least Zn _x1 Cd _x2 Hg _(1-x1-x2) S _y1 Se _y2 Te _{(1-y1- y2)} (0 ≦ x1, x2, y1, y2 ≦ 1).

  The invention according to claim 18 is the invention according to any one of claims 1 to 17, characterized in that at least one light source of the incident two-wavelength light is a semiconductor laser.

  According to a nineteenth aspect of the present invention, in the invention according to any one of the first to seventeenth aspects, at least one light source of the incident two-wavelength light is a YAG laser-pumped optical parametric oscillator.

  The invention according to claim 20 is the invention according to claim 18 or 19, wherein at least one wavelength of the incident two-wavelength light is 1260 nm ≦ λ ≦ 1675 nm (O band, E band, S band, C band, L Band, U band).

  The invention according to claim 21 is the invention according to claim 18 or 19, wherein at least one wavelength λ of the incident two-wavelength light is 1460 nm ≦ λ ≦ 1625 nm (S band, C band, L band). It is characterized by.

  A twenty-second aspect of the invention is characterized in that, in the invention of the eighteenth or nineteenth aspect, a wavelength λ of at least one of the incident two-wavelength light is 1530 nm ≦ λ ≦ 1565 nm (C band).

  The invention according to claim 23 is the invention according to claim 18, wherein the wavelength λ of at least one of the incident two-wavelength light is 900 nm ≦ λ ≦ 1100 nm.

  According to a twenty-fourth aspect of the present invention, in the method for manufacturing an electromagnetic wave generating device according to the first to twenty-third aspects, the thicknesses of the first and second compound semiconductors are made equal to the orientation inversion period by polishing. An adjusting step of adjusting the first and second compound semiconductors to form a joined body, and the joined body includes the first and second compounds. A plane perpendicular to the optical axis at which the spatial symmetry of the semiconductor crystal is inverted is a bonding surface formed by the bonding, and the orientations having azimuth reversal periods that are antiparallel to the optical axis direction at which the spatial symmetry is inverted. It is an inversion structure.

  The invention according to claim 25 is the method of manufacturing an electromagnetic wave generator according to any one of claims 1 to 23, wherein the third compound semiconductor is made of a nonlinear material having the same composition as the first and second compound semiconductors. A preparation step of preparing a third compound semiconductor having a thickness greater than the direction inversion period, and a nonlinear material having the same composition as that of the third compound semiconductor. A first compound perpendicular to an optical axis that is joined to a fourth compound semiconductor having a thickness corresponding to the orientation reversal period and in which the spatial symmetry of the crystals of the third and fourth compound semiconductors is reversed. A joined body forming step of forming joined bodies that are anti-parallel to the optical axis direction in which the spatial symmetry is reversed, and a third surface that forms the joined body. Compound An ion having a constant energy is accelerated by a high electric field from the second surface facing the bonding surface of the semiconductor and is implanted into the third compound semiconductor, and is artificially moved from the bonding surface to a distance corresponding to the orientation inversion period. A cleavage plane forming step for forming a cleavage plane, and a fourth compound semiconductor forming the joined body along the cleavage plane, having a thickness corresponding to the azimuth inversion distance and having the junction plane The method further comprises an orientation reversal structure forming step of cleaving into a semiconductor and the remaining compound semiconductor to make the stacked body an orientation reversal structure having the orientation reversal period.

  The invention described in claim 26 is the method of manufacturing the electromagnetic wave generator according to any one of claims 1 to 23, wherein the third compound semiconductor is made of a nonlinear material having the same composition as the first and second compound semiconductors. A preparation step of preparing a third compound semiconductor having a thickness greater than the orientation inversion period; and from one surface of the third compound semiconductor, ions having constant energy are accelerated by a high electric field, and Cleaving into the third compound semiconductor and forming an artificial cleavage plane at a distance corresponding to the orientation inversion period from the surface or a surface facing the surface; and the orientation inversion period from the artificial cleavage surface The third compound semiconductor is made of a non-linear material having the same composition as the third compound semiconductor so as to be bonded at a surface at a distance corresponding to the distance corresponding to the orientation inversion period. A plane perpendicular to the optical axis at which the spatial symmetry of the crystals of the third and fourth compound semiconductors is reversed is bonded to the fourth compound semiconductor having the thickness, and the space A bonded body forming step of forming a bonded body that is antiparallel to the optical axis direction in which the symmetry is reversed, and a fourth compound semiconductor that forms the bonded body along the cleavage plane, A direction inversion structure forming step of cleaving into a compound semiconductor having a thickness corresponding to a distance and having the bonding surface, and the remaining compound semiconductor to form the stacked body in an direction inversion structure having the direction inversion period It is characterized by having.

  A twenty-seventh aspect of the invention is a method of manufacturing an electromagnetic wave generating device according to the first to twenty-third aspects, wherein the third compound semiconductor is made of a nonlinear material having the same composition as the first and second compound semiconductors. A preparation step of preparing a third compound semiconductor having a thickness greater than the direction inversion period, and a nonlinear material having the same composition as that of the third compound semiconductor. A first compound perpendicular to an optical axis that is joined to a fourth compound semiconductor having a thickness corresponding to the orientation reversal period and in which the spatial symmetry of the crystals of the third and fourth compound semiconductors is reversed. A joined body forming step of forming joined bodies that are anti-parallel to the optical axis direction in which the spatial symmetry is reversed, and a third surface that forms the joined body. Compound Polishing the second surface of the semiconductor facing the bonding surface to adjust the thickness of the third compound semiconductor forming the bonded body to a thickness corresponding to the orientation inversion period. And a process.

  The invention according to claim 28 is the invention according to any one of claims 24 to 27, further comprising a step of bonding the wavelength conversion element having the periodic inversion structure to a support substrate.

  In one embodiment of the present invention, by adopting the above configuration, the narrow line width of the output electromagnetic wave is realized by the steep wavelength selectivity of the quasi phase matching structure. Moreover, since the element length can be made extremely long by adopting the quasi phase matching structure as compared with the difference frequency generation using the bulk nonlinear crystal, high efficiency and high output can be realized. Furthermore, by introducing a confinement structure using a waveguide and increasing the interaction between electromagnetic waves, it is possible to achieve even higher efficiency, and it is cheap, highly efficient, and highly reliable. It is also possible to use a semiconductor laser diode for exciting an optical fiber amplifier as a pumping light source.

  As described above, according to the present invention, an electromagnetic wave having a narrow line width in a range of 0.1 THz to 10 THz can be generated with high efficiency and high output. In addition, in an element having a waveguide structure, since the interaction between electromagnetic waves can be increased as compared with the bulk type, the modulation efficiency can be further increased. As a result, an electromagnetic wave generator can be configured using an inexpensive and highly efficient and reliable semiconductor laser for optical communication or a semiconductor laser diode for exciting a rare earth-doped optical fiber amplifier as an excitation light source.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings described below, components having the same function are denoted by the same reference numerals, and repeated description thereof is omitted.
(First embodiment)
FIG. 1 is a diagram showing an electromagnetic wave generator according to this embodiment. The electromagnetic wave generator according to this embodiment includes a compound semiconductor quasi-phase matching element 100 as a wavelength conversion element and two excitation light sources (not shown) as means for exciting the compound semiconductor quasi-phase matching element 100. Excitation lasers 103 and 104 oscillated from the excitation light source are incident from one surface of the compound semiconductor pseudo phase matching element 100. In this embodiment, the frequency difference between the excitation lasers 103 and 104 is set to 0.1 to 10 THz.

  In this embodiment, the pumping light source of at least one of the pumping lasers 103 and 104 can be a semiconductor laser or a YAG laser pumped optical parametric oscillator. In addition, the optical communication wavelength band (for example, O band (1260 to 1360 nm) that can be amplified by an optical fiber amplifier is used as an inexpensive, high power, and highly reliable light source that is extremely important for industrial applications. ), E band (1360 to 1460 nm), S band (1460 to 1530 nm), C band (1530 to 1565 nm), L band (1565 to 1625 nm) U band (1625 to 1675 nm)), or rare earth doped A 900 to 1100 nm band semiconductor laser diode that has been put to practical use as an excitation light source for an optical fiber amplifier can also be used as an excitation light source for the excitation lasers 102 and 103.

  In FIG. 1, a compound semiconductor quasi-phase matching element 100 includes a compound semiconductor 101 that is a nonlinear material and a compound semiconductor 102 that is a nonlinear material having the same chemical composition as the 101. In the present embodiment, the stacked surface (bonding surface) with each of the compound semiconductors 101 and 102 is a surface perpendicular to the optical axis at which the spatial symmetry of the crystals of the compound semiconductors 101 and 102 is reversed, and the crystals of the compound semiconductors 101 and 102 are The quasi-phase matching element is obtained by performing azimuth reversal at a predetermined period with the optical axis whose spatial symmetry is reversed as the reversal axis.

For the compound semiconductor 101 and 102 Toga閃zinc blende structure, in the compound semiconductor 101 and 102. (110) plane or (110) plane and the crystal equivalent planes (specifically (110), (11 0 ), (1 1 0), ( 1 10), (101), ( 1 0 1 ), (10 1 ), ( 1 01), (011), (0 11 ), (01 1 ), (0 1 1) (Any of the twelve faces of the underline is a substitute for the overline, and the same shall apply hereinafter) are parallel to each other, and a plane that is crystallographically equivalent to the (111) plane or the (111) plane (specifically ( 111), (11 1 ), (1 1 1), ( 1 11), (1 11 ), ( 1 1 1 ), ( 1 1 1 ), ( 11 1) (any one of 8 faces of ( 111 )) in the normal direction On the other hand, the compound semiconductors 101 and 102 are arranged so that the crystal orientations are reversed. By using the (110) plane or a plane that is crystallographically equivalent to the (110) plane as a laminated plane, the second-order nonlinear optical constant can be used effectively.

Further, instead of the (111) plane or the plane that is crystallographically equivalent to the (111) plane, the (100) plane or the plane equivalent to the (100) plane in the compound semiconductors 101 and 102 (specifically, the (100), (1 00), (010), (0 1 0), (001), compound semiconductor 101 as with respect to the normal direction, the crystal orientation is reversed each other six sides of (00 1)) The same effect can be obtained even if the two and 102 are arranged.

When the compound semiconductors 101 and 102 have a wurtzite structure, the (1 1 00) plane or the (1 1 100 ) plane crystallographically equivalent plane (specifically ((1 1 00), (1 100), (01 1 0), (0 1 10), (10 1 0), 6 faces), or (11 2 0) plane or (11 2 0) plane of the (1 010) (Specifically, six surfaces ((11 2 0), ( 11 20), (1 2 10), ( 1 2 1 0), ( 2 110), (2 11 0)) ) Are parallel to each other, and the compound semiconductors 101 and 102 are so arranged that their crystal orientations are reversed with respect to the normal direction of the (0001) plane or the (000 1 ) plane that is crystallographically equivalent to the (0001) plane. May be arranged.

The material of the compound semiconductors 101 and 102 is at least one of III-V group binary compound semiconductors such as GaAs, GaP, AlAs, AlP, InAs, InP, GaN, and InN, and In _x1 that is a mixed crystal thereof. Al _x2 Ga _(1-x1-x2) N _y1 As _y2 P _(1-y1-y2) (where 0 ≦ x1, x2, y1, y2 ≦ 1, x1 + x2 ≦ 1, y1 + y2 ≦ 1). Alternatively, the material of the compound semiconductors 101 and 102 is at least one of II-VI group binary compound semiconductors such as α-ZnS, β-ZnS, ZnSe, ZnTe, ZnO, CdS, CdSe, CdTe, HgTe, ZnS, and the like. Zn _x1 Cd _x2 Hg _{(1-x1-x2) Sy1} Se _y2 Te _(1-y1-y2) (where 0≤x1, x2, y1, y2≤1, x1 + x2≤1, y1 + y2≤) 1) may be used.

In this embodiment, III-V and II-VI compound semiconductors have been described in detail with respect to the laminated surface and orientation inversion surface. However, the present invention is not limited to III-V and II-VI groups, and I belongs to the adamantine series. -III-VI ₂ group and II-IV-V ₂ group (both having chalcopyrite structure), II-III ₂ -VI ₄ group (with de EFFECT chalcopyrite structure) for a multi-source of a compound semiconductor such as the The direction perpendicular to the optical axis where the spatial symmetry of the crystal of the compound semiconductor constituting the structure is inverted is the laminated surface, and the direction is inverted at a predetermined cycle with the optical axis where the spatial symmetry of the crystal is inverted as the inversion axis. The same effect can be obtained.

Further, the thickness Lc (polarization inversion period) of the compound semiconductors 101 and 102 is set to the coherence length obtained by the equation (1), whereby the quasi phase matching condition is achieved, and highly efficient difference frequency light is generated. Is possible.
Lc = n × π / Δk (1) (n: natural number)
However, Δk = 2π / c × (n1, ν1-n2, ν2-n3, ν3)
Here, ν1, ν2, and ν3 are the frequency of the excitation laser beam 103, the frequency of the excitation laser beam 104, and the frequency of the generated electromagnetic wave, respectively, and the relationship in which the difference between ν1 and ν2 is ν3 is established. C is the speed of light.

  In FIG. 1, each of the compound semiconductors 101 and 102 is a 20-layer laminated semiconductor in which 10 semiconductors are bonded to each other using a semiconductor direct bonding technique, but the number of layers may be two or more.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to the following Example, It cannot be overemphasized that it can change variously in the range which does not deviate from the summary.

(First embodiment)
In this embodiment, the compound semiconductors 101 and 102 are GaP in the electromagnetic wave generator shown in FIG. Further, Lc, ν1, and ν2 were set so that the frequency ν3 of the generated electromagnetic wave was 1 THz. In this embodiment, since the compound semiconductors 101 and 102 are GaP, a specific value of Lc is about 0.75 mm.

  Regarding the pump lasers 102 and 103, in this embodiment, a 1550 nm band (C band: 1530 to 1565 nm) generated by using two parametric oscillators (OPO) from pulses from an Nd: YAG laser having a repetition rate of 10 Hz and a pulse width of 10 ns. Each pulsed light was used.

  When the pump lasers 102 and 103 are incident on the compound semiconductor quasi-phase matching element 100 so that their optical axes coincide with each other and are linearly polarized parallel to the azimuth inversion axis using a polarization controller, It was confirmed that high-intensity pulsed electromagnetic waves can be generated with a narrower line width (about 50 GHz) than (400 GHz).

  Even if the optical axes are not matched, the effect itself is essentially not lost, although the efficiency is slightly reduced.

(Second embodiment)
In this example, a method for manufacturing a stacked structure of the compound semiconductor quasi phase matching element 100 shown in FIG. 1 will be described.
10 pairs of GaP substrates (compound semiconductors) 101 and 102 each having a thickness adjusted to Lc by double-sided mirror polishing are cleaned with an organic solvent (acetone, ethanol), sulfuric acid, and hydrofluoric acid, and then sufficiently washed with water. .

  In this example, the above chemical solution was used for surface cleaning, but its purpose is to remove organic substances, inorganic substances, and natural oxide film on the surface. Therefore, any combination of chemical solutions that can achieve these purposes can be used. For example, other types of chemicals can be used. For example, GaAs cannot be used as a surface cleaning solution because the GaAs substrate itself reacts with a sulfuric acid chemical solution. For this reason, hydrochloric acid chemicals are used instead for the purpose of removing inorganic substances.

Thereafter, the GaP substrates 101 and 102 dried by a drying device such as a spinner are alternately superposed on the GaPs 101 and 102 according to the above-described plane orientation. That is, in the GaP substrates 101 and 102, planes that are crystallographically equivalent to the (110) plane or the (110) plane are parallel to each other, and the normal line of the plane that is crystal equivalent to the (111) plane or the (111) plane. The GaP substrates 101 and 102 are bonded so that the crystal orientations are reversed with respect to the direction. At this time, it is already bonded with a weak force due to hydrogen bonding, but dehydration condensation can be achieved by heating at a temperature of 400 ° C. or higher in a hydrogen atmosphere while applying a load of about 100 g / cm ² to the bonding surface of the element and heating for a certain time. As a result, the compound semiconductor quasi-phase matching element 100 having a laminated structure bonded more firmly can be manufactured.

  The joining method used in this example is usually called a direct joining technique. This is an essentially different method from diffusion bonding that is often used to join metals together. Unlike diffusion bonding, a bonding interface produced by direct bonding technology has very little interdiffusion at the interface. Therefore, it is possible to produce an azimuth inversion structure in which the second-order nonlinear polarizability is inverted very steeply, and this makes it possible to minimize a decrease in efficiency due to “sagging” of the interface.

(Third embodiment)
Regardless of the method of the second embodiment, the compound semiconductor quasi-phase matching element 100 can also be manufactured by the method described in this embodiment.
2A to 2H are views showing a method for manufacturing the electromagnetic wave generator according to the present embodiment.
First, a support substrate 105 and a compound semiconductor substrate 106 which is thicker than the thickness Lc and whose upper surface is a (110) plane (or a (110) plane crystal equivalent surface) are prepared (FIG. 2A). Then, the compound semiconductor substrate 106 is directly bonded to the support substrate 105 by the direct bonding technique described in the second embodiment (also simply referred to as direct connection) (FIG. 2B). Here, the compound semiconductor substrate 106 is made of GaAs. The support substrate 105 is made of a material that can be selectively removed by etching or the like such as quartz or InP substrate, or has a crystal orientation of (110) plane (or (110) plane crystal equivalent). A GaAs substrate having an orthogonal (100) plane (or a (100) plane crystal equivalent surface) may be used.

  After direct bonding, hydrogen ions having constant energy are accelerated from a top surface of the compound semiconductor substrate 106 by a high electric field by accelerating the compound semiconductor substrate 106 (also simply referred to as hydrogen ion implantation), and then annealed to cleave the surface 107. Is artificially formed (FIG. 2C). Note that the hydrogen ion implantation energy at this time is set so that the distance from the lower surface of the compound semiconductor substrate 106 (the surface facing the surface into which the hydrogen ions are implanted) to the cleavage surface 107 is the inversion period Lc.

  Here, as a feature of the ion implantation method, the implanted hydrogen ions remain at a depth corresponding to the kinetic energy, and the bonds between the atoms in the vicinity of the remaining ions can be broken. The trajectory through which the hydrogen ions have passed is also subjected to crystal damage, but damage caused by the passage of hydrogen ions can be recovered by annealing. The relationship between the kinetic energy of the implanted hydrogen ions and the implantation depth has extremely high reproducibility, so by implanting and implanting the energy of the implanted hydrogen ions to a certain depth, Only interatomic bonds can be selectively broken. That is, it can be easily cleaved with the surface formed at the depth as a boundary. Therefore, the surface formed in this way and having a certain distance from the upper surface of the substrate into which hydrogen ions are implanted (a distance corresponding to the energy of the implanted hydrogen ions) is a cleavage plane.

  After the compound semiconductor substrate 106 is cleaved into the substrate 108 having the thickness Lc and the remaining substrate 109 (FIG. 2D), the compound semiconductor substrate 110 having a thickness larger than the thickness Lc is changed to the substrate 108 and the (111) plane. With respect to the normal direction of (or (111) plane crystal equivalent surface), the crystal orientation is reversed and the layers are directly joined (FIG. 2 (e)). Next, as described above, hydrogen ions are implanted so that the distance from the upper surface of the compound semiconductor substrate 110 to the cleavage surface 111 from the lower surface of the compound semiconductor substrate 110 is the inversion period Lc, and then annealed to thereby cleave the cleavage surface. 111 is artificially formed (FIG. 2F). Next, the compound semiconductor substrate 110 is cleaved into the substrate 112 having a thickness Lc and the remaining substrate 113 (FIG. 2G).

  The compound semiconductor quasi-phase matching element 100 having the same characteristics as those of the first embodiment can also be manufactured by alternately repeating such direct bonding, ion implantation, annealing, and cleavage processes on the substrate 106 and the substrate 110. Is possible (FIG. 2 (g)).

  The manufacturing method according to this example can be applied even when Lc is thin and it is difficult to adjust the thickness by polishing as in the second example, and the substrate 109 and the substrate 113 after cleavage can be reused. It is a feature that it is possible.

(Fourth embodiment)
In the third embodiment, hydrogen ions are implanted after bonding each compound semiconductor. In this embodiment, before the compound semiconductor is joined, hydrogen ions are implanted into one compound semiconductor to form an artificial cleavage plane.

  In this example, first, a first compound semiconductor substrate having a thickness larger than the thickness Lc and having an upper surface of (110) plane (or a (110) plane crystal equivalent surface) is prepared. Hydrogen ions are implanted into the opposite surface, and then annealed to artificially form a cleavage plane on the upper surface or a surface at a distance Lc from the opposite surface.

  Next, the surface of the first compound semiconductor substrate at a distance Lc from the cleavage surface is directly bonded to the support substrate. The joined body of the support substrate and the first compound semiconductor substrate thus formed is the same as that shown in FIG. Next, in the same manner as in the third embodiment, the first compound semiconductor substrate having the thickness Lc on the support substrate is obtained by cleaving the first compound semiconductor substrate into the substrate having the thickness Lc and the remaining substrate. Form.

  Next, a second compound semiconductor substrate that is thicker than the thickness Lc and whose upper surface is a (110) plane (or may be a (110) plane crystal equivalent surface) is prepared, and the upper surface or a surface facing it is prepared. Hydrogen ions are implanted and then annealed to artificially form a cleavage plane on the surface at a distance Lc from the upper surface or the surface facing the upper surface. Next, the surface of the second compound semiconductor substrate at a distance Lc from the cleavage plane and the upper surface of the first compound semiconductor formed on the support substrate are (111) plane (or (111) plane crystallographically). It is arranged so that the crystal orientation is reversed with respect to the normal direction of the equivalent plane) and directly joined. Next, the second compound semiconductor is cleaved into a substrate having a thickness Lc and the remaining substrate.

  By repeating hydrogen ion implantation, direct bonding, and cleavage, the compound semiconductor quasi-phase matching element 100 having the same characteristics as those of the first embodiment can be manufactured.

(Fifth embodiment)
Regardless of the method described above, the compound semiconductor pseudo phase matching element 100 can also be manufactured by the method described in this embodiment.
3A to 3F are views showing a method for manufacturing the electromagnetic wave generator according to the present embodiment.
In the manufacturing method according to the second example, ion implantation was performed so as to obtain a substrate having a thickness Lc by cleavage, and then the substrate was cleaved.

In contrast, in this embodiment, a support substrate 105 and a compound semiconductor substrate 106 whose upper surface is a (110) plane (or a (110) plane crystal equivalent surface) are prepared (FIG. 3A). )) After the compound semiconductor substrate 106 is directly bonded to the support substrate 105 (FIG. 3B), the thickness of the upper surface of the compound semiconductor substrate 106 is adjusted to Lc by polishing (FIG. 3C). Thereafter, the compound semiconductor substrate 110 is arranged so that the crystal orientation is reversed and directly bonded (FIG. 3D), and the upper surface of the compound semiconductor substrate 110 is adjusted to Lc by polishing (FIG. 3E). . By repeating such steps sequentially, it is possible to produce a structure similar to that of the first embodiment (FIG. 3F).
Needless to say, the second to fifth embodiments can be combined.

(Second Embodiment)
In the first embodiment, the structure and manufacturing method of the bulk type compound semiconductor quasi-phase matching element have been described. However, in this embodiment, at least one or both of excitation light and generated electromagnetic waves are confined in the waveguide. By doing in this way, the efficiency of difference frequency generation can be improved.

FIG. 4 is a diagram showing the compound semiconductor quasi-phase matching element according to the present embodiment. In this embodiment, as shown in FIG. 4, a waveguide is formed from an element having a bulk structure.
In FIG. 4, reference numeral 114 denotes a support substrate, and in this embodiment, the material is quartz. The compound semiconductor quasi-phase matching element 100 and the support substrate 114 described in the first embodiment are bonded and integrated with polyimide. Next, as shown in FIG. 5, the element is covered with a quartz pipe 115 whose inner surface is coated with a metal, and the remaining gap is filled with a resin 116 matching the refractive index of quartz, whereby a waveguide element as shown in FIG. Can be produced.

  In forming the waveguide as shown in FIG. 4, the compound semiconductor quasi-phase matching element 100 according to the first embodiment is cut in a direction perpendicular to the bonding surface so as to have a predetermined width. 114 may be joined. In addition, the compound semiconductor pseudo phase matching element 100 is bonded to the support substrate 114 without performing the above-described cutting, and then the compound semiconductor pseudo phase matching element 100 is cut by dicing or the like so as to have a predetermined width. You may do.

  Since the waveguide type compound semiconductor quasi-phase matching element manufactured in this embodiment can be strongly confined, in addition to the Nd: YAG laser-pumped OPO, it is extremely important for industrial application, inexpensive and high power and As a reliable light source, an optical communication wavelength band (for example, O band (1260 to 1360 nm), E band (1360 to 1460 nm), S band (1460 to 1530 nm), C band (which can be amplified by an optical fiber amplifier) 1530 to 1565 nm), L band (1565 to 1625 nm), U band (1625 to 1675 nm)), or 900 to 1100 nm band semiconductor laser diode that has been put to practical use as a pumping light source for rare earth doped optical fiber amplifiers And the like, and the excitation light sources of the excitation lasers 102 and 103 It can be used Te.

  In this embodiment, quartz is used for the support substrate 114, but any material that is transparent at the three frequencies that generate the difference frequency may be used. In addition, polyimide is used for bonding the support substrate 114 and the compound semiconductor quasi phase matching element 100, but a general optical adhesive may be used, or bonding may be performed under high temperature and high pressure by a direct bonding technique. . In addition, since the object is achieved if the manufactured structure is a waveguide for the generated electromagnetic wave, the resin 116 does not necessarily match the refractive index of the support substrate, and the pipe whose inner surface is metal-coated. The shape may be other than a square.

  In this embodiment, the waveguide for electromagnetic waves of 0.1 to 10 THz is a waveguide by plasma confinement using a metal wall generally used in the microwave region, but is generally used in the optical region. The same effect can be obtained even with a waveguide structure using a refractive index confinement utilizing the refractive index difference.

  In this embodiment, the substrate that supports the waveguide is used. However, the support substrate is not necessarily required.

  In the embodiment of the present invention, the semiconductor compound is joined by direct joining. However, the present invention is not limited to this, and any method may be used as long as two compound semiconductors can be joined.

It is a figure which shows the electromagnetic wave generator which concerns on one Embodiment of this invention. (A)-(h) is a figure which shows the preparation methods of the electromagnetic wave generator which concerns on one Example of this invention. (A)-(f) is a figure which shows the preparation methods of the electromagnetic wave generator which concerns on one Example of this invention. It is a figure which shows the compound semiconductor pseudo phase matching element which concerns on one Embodiment of this invention. It is a figure which shows the compound semiconductor pseudo phase matching element which concerns on one Embodiment of this invention.

Explanation of symbols

100 Compound Semiconductor Quasi-Phase Matching Element 101, 102 Compound Semiconductor 103, 104 Excitation Laser

Claims (28)

When two-wavelength light having a frequency difference set to 0.1 to 10 GHz is incident, the electromagnetic wave generation includes a quasi-phase matching type wavelength conversion element that generates an electromagnetic wave of 0.1 to 10 THz by the difference frequency generation by the two-wavelength light. In the device
The wavelength conversion element has a first compound semiconductor and a second compound semiconductor made of a nonlinear material that is a group III-V or group II-VI compound semiconductor having the same composition,
The first and second compound semiconductors are joined together to form a joined body;
The joined body has an optical axis direction in which the spatial symmetry is reversed with a surface perpendicular to the optical axis in which the spatial symmetry of the crystals of the first and second compound semiconductors is reversed as a joined surface formed by the joining. Is an azimuthal inversion structure having azimuth inversion cycles antiparallel to each other,
ν1 and ν2 are the frequencies of the incident two-wavelength light, ν3 is the generated electromagnetic wave frequency of 0.1 to 10 THz, and n1, n2, and n3 are the refractive indexes of the nonlinear materials at frequencies ν1, ν2, and ν3, respectively. , C is the speed of light, and Δk = 2π / c × (n1, ν1-n2, ν2-n3, ν3), the direction inversion period is a natural number multiple of π / Δk. . Further comprising a waveguide for the electromagnetic wave of 0.1 to 10 THz,
The electromagnetic wave generator according to claim 1, wherein the wavelength conversion element is disposed in the waveguide. Further comprising excitation means for exciting each of the two-wavelength light incident on the wavelength conversion element,
2. The two-wavelength light is incident on the wavelength conversion element from the excitation means to generate the electromagnetic wave of 0.1 to 10 THz, and the generated electromagnetic wave of 0.1 to 10 THz is output. Or the electromagnetic wave generator of 2.   3. The electromagnetic wave generator according to claim 2, wherein the waveguide for the electromagnetic wave of 0.1 to 10 THz is formed by plasma confinement.   3. The electromagnetic wave generator according to claim 2, wherein the waveguide for the electromagnetic wave of 0.1 to 10 THz is based on a refractive index confinement.   6. The electromagnetic wave generator according to claim 1, wherein the nonlinear material has a zinc blende structure. The joint surface is a (110) plane or a plane that is crystallographically equivalent to the (110) plane,
7. The electromagnetic wave generator according to claim 6, wherein the optical axis direction in which the spatial symmetry is reversed is a [111] axis, a [100] axis, or a crystal axis direction equivalent to these.   The electromagnetic wave generator according to claim 6 or 7, wherein the group III-V compound semiconductor contains at least one of GaAs, GaP, and InP. The III-V group compound semiconductor is at least In _x1 Al _x2 Ga _{(1-x1-x2) Ny1} As _y2 P _(1-y1-y2) (0 ≦ x1, x2, y1, y2 ≦ 1, x1 + x2 ≦ 1 , Y1 + y2 ≦ 1). 6. The electromagnetic wave generator according to 6 or 7, wherein   The electromagnetic wave generator according to claim 6 or 7, wherein the II-VI group compound semiconductor contains at least one of β-ZnS, ZnSe, or ZnTe. The II-VI group compound semiconductor is at least Zn _x1 Cd _x2 Hg _{(1-x1-x2) Sy1} Se _y2 Te _(1-y1-y2) (0 ≦ x1, x2, y1, y2 ≦ 1, x1 + x2 ≦ 1 , Y1 + y2 ≦ 1), The electromagnetic wave generator according to claim 6 or 7.   6. The electromagnetic wave generator according to claim 1, wherein the nonlinear material has a wurtzite structure. The joint surface is a (1100) surface or a (1120) surface, or a surface that is crystallographically equivalent to these,
13. The electromagnetic wave generator according to claim 12, wherein an optical axis direction in which the spatial symmetry is reversed is a [0001] axis direction.   The electromagnetic wave generator according to claim 12 or 13, wherein the III-V group compound semiconductor contains at least GaN. The III-V group compound semiconductor is at least In _x1 Al _x2 Ga _{(1-x1-x2) Ny1} As _y2 P _(1-y1-y2) (0 ≦ x1, x2, y1, y2 ≦ 1, x1 + x2 ≦ 1 , Y1 + y2 ≦ 1), The electromagnetic wave generator according to claim 12 or 13.   The electromagnetic wave generator according to claim 12 or 13, wherein the II-VI group compound semiconductor contains at least one of α-ZnS, ZnO, CdS, CdSe, or CdTe. The II-VI group compound semiconductor contains at least Zn _x1 Cd _x2 Hg _{(1-x1-x2) Sy1} Se _y2 Te _(1-y1-y2) (0 ≦ x1, x2, y1, y2 ≦ 1). The electromagnetic wave generator according to claim 12 or 13, wherein the electromagnetic wave generator is provided.   18. The electromagnetic wave generator according to claim 1, wherein at least one light source of the incident two-wavelength light is a semiconductor laser.   18. The electromagnetic wave generator according to claim 1, wherein at least one of the incident two-wavelength light sources is a YAG laser-pumped optical parametric oscillator.   20. The wavelength of at least one of the incident two-wavelength light is 1260 nm ≦ λ ≦ 1675 nm (O band, E band, S band, C band, L band, U band). Electromagnetic wave generator.   20. The electromagnetic wave generator according to claim 18, wherein at least one wavelength λ of the incident two-wavelength light satisfies 1460 nm ≦ λ ≦ 1625 nm (S band, C band, L band).   20. The electromagnetic wave generator according to claim 18, wherein a wavelength λ of at least one of the incident two-wavelength light satisfies 1530 nm ≦ λ ≦ 1565 nm (C band).   19. The electromagnetic wave generator according to claim 18, wherein the wavelength λ of at least one of the incident two-wavelength light satisfies 900 nm ≦ λ ≦ 1100 nm. 24. A method of manufacturing an electromagnetic wave generator according to claim 1, comprising:
An adjusting step of adjusting the thicknesses of the first and second compound semiconductors to be equal to the orientation inversion period by polishing;
A joined body forming step of joining the adjusted first and second compound semiconductors to form a joined body,
The bonded body has an optical axis direction in which the spatial symmetry is reversed, with a plane perpendicular to the optical axis in which the spatial symmetry of the crystals of the first and second compound semiconductors is reversed as a bonded surface formed by the bonding. A method for manufacturing an electromagnetic wave generator, characterized in that the structure has an azimuth reversal structure having azimuth reversal periods antiparallel to each other. 24. A method of manufacturing an electromagnetic wave generator according to claim 1, comprising:
A preparation step of preparing a third compound semiconductor made of a nonlinear material having the same composition as the first and second compound semiconductors and having a thickness greater than the orientation inversion period;
The prepared third compound semiconductor is joined to a fourth compound semiconductor made of a nonlinear material having the same composition as the third compound semiconductor and having a thickness corresponding to the orientation inversion period. The first surface perpendicular to the optical axis at which the spatial symmetry of the crystals of the third and fourth compound semiconductors is inverted is defined as a bonding surface formed by the bonding, and the optical axis direction at which the spatial symmetry is inverted is mutually A joined body forming step of forming a joined body that is antiparallel;
From the second surface of the third compound semiconductor that forms the bonded body, the ions having a constant energy are accelerated by a high electric field from the second surface facing the bonding surface, and are implanted into the third compound semiconductor. A cleavage plane forming step of forming an artificial cleavage plane at a distance corresponding to the azimuth inversion period;
Along the cleavage plane, a fourth compound semiconductor that forms the joined body is cleaved into a compound semiconductor having a thickness corresponding to the azimuth inversion distance and the junction surface and the remaining compound semiconductor. And an orientation reversal structure forming step in which the laminated body has an orientation reversal structure having the orientation reversal period. 24. A method of manufacturing an electromagnetic wave generator according to claim 1, comprising:
A preparation step of preparing a third compound semiconductor made of a nonlinear material having the same composition as the first and second compound semiconductors and having a thickness greater than the orientation inversion period;
From one surface of the third compound semiconductor, ions having constant energy are accelerated by a high electric field and implanted into the third compound semiconductor, and a distance corresponding to the orientation inversion period from the surface or a surface facing the surface. A cleaved surface forming step for forming an artificial cleaved surface on the surface,
The third compound semiconductor is made of a non-linear material having the same composition as the third compound semiconductor so that the third compound semiconductor is bonded to a surface at a distance corresponding to the orientation inversion period from the artificial cleavage plane, and the orientation inversion is performed. A junction formed by joining to a fourth compound semiconductor having a thickness corresponding to a period and having a plane perpendicular to the optical axis at which the spatial symmetry of the crystals of the third and fourth compound semiconductors is reversed. As a surface, a joined body forming step of forming joined bodies that are antiparallel to the optical axis direction in which the spatial symmetry is reversed, and
Along the cleavage plane, a fourth compound semiconductor that forms the joined body is cleaved into a compound semiconductor having a thickness corresponding to the azimuth inversion distance and the junction surface and the remaining compound semiconductor. And an orientation reversal structure forming step in which the laminated body has an orientation reversal structure having the orientation reversal period. 24. A method of manufacturing an electromagnetic wave generator according to claim 1, comprising:
A preparation step of preparing a third compound semiconductor made of a nonlinear material having the same composition as the first and second compound semiconductors and having a thickness greater than the orientation inversion period;
The prepared third compound semiconductor is joined to a fourth compound semiconductor made of a nonlinear material having the same composition as that of the third compound semiconductor and having a thickness corresponding to the orientation inversion period. The first surface perpendicular to the optical axis at which the spatial symmetry of the crystals of the third and fourth compound semiconductors is inverted is defined as a bonding surface formed by the bonding, and the optical axis direction at which the spatial symmetry is inverted is mutually A joined body forming step for forming a joined body that is anti-parallel;
The thickness of the third compound semiconductor forming the bonded body is determined by polishing the second compound semiconductor forming the bonded body with respect to the second surface facing the bonded surface. And a polishing step of adjusting to a thickness corresponding to the reversal period. 28. The method for manufacturing an electromagnetic wave generating device according to claim 24, further comprising a step of bonding the wavelength conversion element having the periodic inversion structure to a support substrate.

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