JPH07281216A - Optical frequency conversion element - Google Patents

Abstract

PURPOSE:To obtain frequency conversion light of light intensity sufficient for practicable use of a conversion element of a signal light frequency using a semiconductor laser by omitting an operation for optical axis alignment, etc., for inputting pumping light to this semiconductor laser. CONSTITUTION:An optical resonator 10 of the Fabry-Perot resonator type semiconductor laser is provided with a grating 12 for phase matching. The pumping light is laser oscillated by this optical resonator 10 and signal light is inputted to the optical resonator 10. The signal light subjected to a frequency conversion is (frequency conversion light) is formed by differential frequency mixing of the pumping light and the input signal light. The phase matching between the pumping light, the signal light and the conversion light is executed by providing the above element with the grating 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical frequency conversion device constructed by using a semiconductor laser.

[0002]

2. Description of the Related Art Conventionally, an optical frequency conversion method using a semiconductor laser as a nonlinear optical medium has been proposed. For example, there is a method using four-wave mixing and a method disclosed in Japanese Patent Laid-Open No. 2-68528.

In four-wave mixing, a current below an oscillation threshold is injected into an optical resonator of a semiconductor laser to amplify light in the optical resonator. This improves the efficiency of frequency conversion. At the same time, signal light of frequency F ₁ and pump light of frequency F ₂ (F ₁ <F ₂ ) are individually generated by the light sources outside the optical resonator, and these lights are input into the optical resonator. When these lights are input, the number of electron carriers in the optical resonator becomes frequency F ₂ −
It vibrates at F ₁ , and the input signal light and the pump light are modulated by this vibration. As a result, the frequency F ₁ − (F ₂ −F
₁ ) and F ₂ + (F ₂ −F ₁ ) frequency converted light is generated.

When a semiconductor laser is used as an optical frequency conversion element, an antireflection film is usually provided on the end face of the optical resonator,
This eliminates the resonance characteristics of the optical resonator and widens the frequency band in which optical amplification is possible.

[0005]

However, in the above-mentioned conventional optical frequency conversion, the light sources of the signal light and the pump light are individually provided outside the optical resonator, and the light generated by these light sources is supplied to the optical resonator. Input into the constituent active layers. Therefore, it is necessary to align the optical axes and further narrow the light beam so that both the signal light and the pump light are input to the active layer. However, since the cross-sectional area of the active layer is generally a very small area of about several μm ^2, the work of inputting both the signal light and the pump light into the active layer is a difficult work.

Further, in the above-mentioned conventional optical frequency conversion, since the frequency converted light is generated by the oscillation of the number of electron carriers, the variable range of the optical frequency is narrow and limited to about several GHz.

A first object of the present invention is to provide an optical frequency conversion element in which a semiconductor laser is used as a non-linear optical medium and also as a pump light source in order to solve the above-mentioned conventional problems. It is in.

A second object of the present invention is to broaden the variable range of the optical frequency in the optical frequency conversion element in which the semiconductor laser is used as the nonlinear optical medium and also as the pump light source. is there.

A third object of the present invention is to use a semiconductor laser as a nonlinear optical medium and also as a pump light source in an optical frequency conversion element in which pump light and / or input signal light becomes noise light. This is to prevent output to the next-stage optical component.

[0010]

In order to achieve this first object, the optical frequency conversion element of the present invention is such that a signal light is input and a pump light for frequency conversion of the input signal light is lased. Optical resonator and a phase matching grating provided in the optical resonator, the grating has concave portions and convex portions provided alternately and periodically in the optical waveguide direction, and the concave portion of the grating is expressed by the following formula ( a) forms a first region having _a first propagation constant difference Δk _a, and the convex portion of the grating has a second propagation constant difference Δ represented by the following equation (b).
and forming a second region having k _b .

[0011] _{Δk a · l a = s ·} π ...... (a) _{However, Δk a = k 3a -k 2a} -k 1a, s is an odd number (s = 1,
3,5, ......) k _3a: first propagation constant of the pump light in the region k _2a: first input signal light in the region propagation constant k _1a: propagation constant l _a frequency converted light in the first region : length of the first region in the optical waveguide direction _{Δk b · l b = s ·} π ...... (b) _{where, Δk b = k 3b -k 2b} -k 1b k 3b: the pump light in the second region propagation constant k _2b: the length of the second region in the optical waveguide direction: second propagation constant k _1b of the input signal light in the region of: propagation constant l _b of the frequency-converted light in the second region

[0012]

With this structure, the pump light having the frequency f ₃ is oscillated in the optical resonator. At the same time, a signal light of frequency f ₂ is generated by a light source outside the optical resonator, and this signal light is input into the optical resonator. As a result, due to the difference frequency mixing of the pump light of the frequency f ₃ and the signal light of the frequency f ₂ , the frequency conversion light of the frequency f ₁ (f ₁ = f ₃ −f ₂ , f ₃ > f _3
2 ) can be generated.

The pump light, the signal light, and the frequency-converted light alternately pass through the first and second regions and are guided inside the optical resonator. Moreover, the first region is _{Δk a · l a = s ·} π
And _a second region has a second propagation constant difference Δk _a represented by Δk _b · I _b = s · π.
have k _b . Therefore, by these first and second regions, the phase shift (phase difference) between the pump light, the input signal light, and the frequency conversion light, more specifically, the band wave (Boun wave)
Since the phase difference can be compensated so that the phase difference between the d Wave) and the free wave (Free Wave) becomes 2 · s · π, the output intensity of the frequency-converted light can be increased.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the drawings are merely schematic representations so that the invention can be understood, and therefore the invention is not limited to the illustrated examples.

FIG. 1 is a sectional view schematically showing the structure of the first embodiment of the present invention, showing a section taken along the optical waveguide direction through the active layer of the optical resonator.

As shown in the figure, the optical frequency conversion element of this embodiment is provided with an optical resonator 10 which receives signal light and which oscillates pump light for frequency conversion of the input signal light. And a grating 12 for phase matching provided in the optical resonator 10. The grating 12 has concave portions 12a and convex portions 12b that are provided alternately and periodically in the optical waveguide direction P, and the concave portion 12a has a first region having _a first propagation constant difference Δk _a represented by the following equation (a). 14 and the convex portion 12b forms the second propagation constant difference Δ represented by the following equation (b).
Form a second region 16 having k _b .

[0017] _{Δk a · l a = s ·} π ...... (a) _{However, Δk a = k 3a -k 2a} -k 1a, s is an odd number (s = 1,
3, 5, ...) k _3a : Propagation constant of pump light in the first region 14 k _2a : Propagation constant of input signal light in the first region 14 k _1a : Propagation of frequency-converted light in the first region 14 constant l _a: length of the first region 14 in the optical waveguide direction _{P Δk b · l b = s} · π ...... (b) _{where, Δk b = k 3b -k 2b} -k 1b k 3b: second propagation constant k _2b of the pump light in the region 16: second propagation constant of the input signal light in the region 16 k _1b: second propagation constant of the frequency-converted light in the region 16 l _b: the second region in the optical waveguide direction P The length of 16 The optical resonator 10 is provided on the first clad layer 18, the active layer 20 and the second clad layer 22 sequentially provided on the clad layer 18, and on one end side of the active layer 20. And the other provided on the side of the other end of the one light reflector 24 and the active layer 20. And a light reflector 26 of.

When the pump light, the input signal light and the frequency conversion light are guided inside the optical resonator 10, the optical waveguide region is mainly the active layer 20. The first region 14 is a region of the optical waveguide region corresponding to the grating concave portion 12a, and the second region 16 is a region of the optical waveguide region corresponding to the grating convex portion 12b. The optical waveguide direction P is along the active layer 10.

First and second propagation constant differences Δk _a and Δk
_b can be controlled by the effective refractive index (also called effective refractive index or equivalent refractive index) of these regions 14 and 16. The effective refractive index of these regions 14 and 16 can be controlled by, for example, the refractive index of the forming material of each element forming the optical resonator 10 and the depth D (see FIG. 1) of the grating 12.
Therefore, for example, the desired propagation constant differences Δk _a and Δk _b can be obtained by arbitrarily and appropriately selecting the forming material and the depth D of each element constituting the optical resonator 10.

The recess 12a of the grating 12 has _a length l _a and the projection 12b has a length l _b , and the recess 12a and the projection 12b are provided alternately along the optical waveguide direction P.

If the first and second regions 14 and 16 formed by the adjacent concave portion 12a and convex portion 12b are phase matching regions for one cycle, the pump light, the signal light and the frequency conversion light will make one cycle. By passing through the phase matching regions 14 and 16 of the minute, more specifically, between these lights, a band wave (Free Wave) and a free wave (Free Wave)
) And (Δk _a · l _a ) + (Δk _b · l _b ) =
A phase shift (phase difference) represented by 2 · s · π occurs.
In this way, since the phase difference can be compensated so that the phase difference becomes 2 · s · π for each of the phase matching regions 14 and 16 for one cycle,
By the phase matching, it is possible to obtain frequency-converted light having a practically satisfactory light output intensity. For example, s = 1.

When the grating 12 is not provided, the phase difference between the pump light, the input signal light, and the frequency conversion light, more specifically, the phase difference between the band wave (Bound Wave) and the free wave (Free Wave) is It is easy to deviate from 2 · s · π, and as a result, it is difficult to obtain frequency-converted light having a practically sufficient optical output intensity due to the phase deviation. To eliminate this, the grating 12 is provided.

[0023], the design must optical frequency conversion element, the frequency f ₃ of the pump light, to select any suitable predetermined design value as the frequency f ₁ of the frequency f ₂ and the frequency-converted light of the input signal light. For example, c / f ₃ = 0.8 μm, c / f ₂ = 1.
65 μm and c / f ₁ = 1.55 μm (c is the speed of light). And, with these frequencies f _{1 to} f ₃ being constant,
Design conditions may be set so as to satisfy the expressions (a) and (b). The design conditions are, for example, the effective refractive index of the first and second regions 14 and 16, the depth D of the grating 12, the length l _a of the concave portion 12a and the length l _b of the convex portion 12b.

When the frequency of the input signal light is converted, the pump light having the frequency f ₃ is oscillated in the optical resonator 10. At the same time, a signal light having a frequency f ₂ is generated by a light source (not shown) outside the optical resonator 10, and this signal light is input into the optical resonator. Then, the frequency-converted light of the frequency f ₁ (f ₁ = f ₃ −f ₂ , f ₃ > f ₂ ) is generated by the difference frequency mixing. The frequency-converted light is emitted from the optical resonator 10 as frequency-converted signal light.

In order to widen the variable range of the frequency f ₁ of the frequency-converted light, 1) the frequency at the absorption edge of the optical resonator 10, particularly the frequency at the absorption edge of the active layer 20, is set to the frequency f of the input signal light.
₂ and the frequency f ₁ of the frequency converted light is preferably higher. Alternatively, 2) a frequency f ₃ of the laser oscillation frequency or the pump light of the optical resonator 10, preferably larger than the frequency f ₁ of the frequency f ₂ and the frequency-converted light of the input signal light.

The optical resonator 1 according to 1) or 2)
The optical waveguide region of 0 can be made substantially transparent to the light of the frequencies f ₂ and f ₁ , so that the dispersion of the refractive index in the optical waveguide region of the optical resonator 10 can be changed to the frequencies of f ₂ and f _1. Can be made very small with respect to the light. If laser oscillation is performed so that the frequency f ₃ of the pump light is kept substantially constant at the design value while the dispersion of the refractive index is extremely small, even if the frequency f ₂ of the input signal light is deviated from the design value, And in the second regions 14 and 16 the formulas (a) and (b)
Can be approximately satisfied.

For example, s = 1. Then, the designed values of the frequency f ₂ of the input signal light and the frequency f ₁ of the frequency-converted light are values that are considered preferable in the current optical communication technology,
When c / f ₂ = 1.65 μm and c / f ₁ = 1.55 μm, the design value of the pump light frequency f ₃ is c / f
₃ = 0.8 μm should be set. Here, the wavelength λ ₂ (= c / f ₂ ) of the input signal light is changed to the wavelength λ ₃ (= c /
It is about twice as large as f ₃ ). In this case, the formulas (a) and (b) can be approximately satisfied in the first and second regions 14 and 16 even if the wavelength λ ₂ of the input signal light is changed within the design value ± 50 nm. Therefore, the frequency f ₁ of the frequency-converted light can be changed in a wider range than before.

FIG. 2 is a sectional view schematically showing the structure of the first embodiment of the present invention, and shows a section taken along the line II--II in FIG.

In this embodiment, the optical resonator 10 is a semiconductor laser 38. The structure and forming material of the semiconductor laser 38 can be variously changed, but here, as an example, the semiconductor laser 38 is a Fabry-Perot resonator type semiconductor laser,
For example, the semiconductor laser 38 is constructed as follows. That is, n-Al _X Ga is sequentially formed on the n-GaAs substrate 28.
_1-X As first cladding layer 18, n or p-Al _Y Ga
_1-Y As active layer 20 (where X> Y) and p-Al _X G
An a _1-X As second cladding layer 22 is provided. Each of these layers 1
8, 20 and 22 are extended in stripes in the optical waveguide direction P, and one side of each of these layers 18, 20 and 22 is embedded with a current confinement layer 30 and the other side is embedded with a current confinement layer 32. . The current confinement layer 30 is sequentially disposed on the substrate _{28 p-Al v Ga 1-} v As layer 30a and the n-A
l _v Ga _1-v consists As layer 30b, a current confinement layer 32 p-Al were sequentially formed on the substrate 28 _v Ga _1-v As layer 3
Consisting 2a and _{n-Al v Ga 1-v} As layer 32b. Further, the cleavage planes 40 and 4 are formed on one and the other ends of the active layer 20, respectively.
2 is formed, and these cleaved surfaces 40 and 42 are connected to the optical resonator 10
Light reflectors 24 and 26. In this case, the Fabry-Perot resonator type semiconductor laser 38 and thus the optical resonator 10 is
Active layer 20, cladding layers 18 and 22, current confinement layer 30,
32 and light reflectors 24, 26.

The arrangement position of the grating 12 can be any suitable position where the effective refractive index of the first and second regions 14 and 16 can be controlled. Here, the active layer 2 is used.
0 and the interface between the second cladding layer 22.

Regarding the optical frequency conversion device having the structure shown in FIGS. 1 and 2, the relationship between the total length L of the grating (see FIG. 1) and the optical power density of the frequency converted light was examined by numerical analysis, and the results are shown in FIG. Shown in. The total length L is the total length of the grating 12 in the optical waveguide direction P. In this numerical analysis, the total length L [m
m] was variously changed to obtain the optical power density [kW / cm ² ] of the frequency-converted light.

Pump light wavelength λ ₃ (= c / f ₃ ): 0.8 μm Pump light power density P ₃ : 10 ⁸ W / cm ² Input signal light wavelength λ ₂ (= c / f ₂ ): 1 .65 μm Power density of input signal light P ₂ : 10 ⁶ W / cm ² Wavelength of frequency-converted light λ ₁ (= c / f ₁ ): 1.55 μm Cladding layers 18 and 22: Al _0.15 Ga _0.85 As layer Active layer 20 : Al _0.3 Ga _0.7 As layer Non-linear optical constant of the cladding layers 18 and 22: 0.2 nm /
V Nonlinear Optical Constant of Active Layer 20: 0.18 nm / V Thickness of Active Layer 20 in First Region 14: 0.1 μm Thickness of Active Layer 20 in Second Region 16: 0.4 μm Activity to Pump Light Refractive index of layer 20: 3.314 Refractive index of active layer 20 for input signal light: 3.306 Refractive index of active layer 20 for frequency converted light: 3.593 Refractive index of cladding layers 18, 22 for pump light: 3 ．
265 Refractive index of the cladding layers 18 and 22 with respect to the input signal light:
3.258 Refractive index of the cladding layers 18 and 22 with respect to the frequency converted light:
3.461 Length l _a of first region 14: 1.45 μm Length l _b of second region 16: 1.85 μm Cross-sectional area of the active layer 20 in the direction orthogonal to the optical waveguide direction P: 1 μm ² As can be understood from FIG. 3, the output intensity of the frequency-converted light increases as the total length L becomes longer. Further, under the above-mentioned conditions, for example, by inputting an input signal light having an optical power of 1 mW with a total length L = 0.4 mm,
It is possible to obtain frequency-converted light having an optical power on the order, and thus it is possible to obtain frequency-converted light having a practically sufficient optical power.

4 and 5 are sectional views schematically showing the construction of the second embodiment of the present invention. In FIG. 4, a cross section taken through the active layer 20 along the optical waveguide direction P, and FIG.
In that case, a cross section taken along line VV in FIG. 4 is shown.
Hereinafter, mainly different points from the first embodiment will be described,
Detailed description of the same points as those in the first embodiment will be omitted.

In this example, n-Al _W Ga _1-W As
An optical guide layer 34 is provided between the first cladding layer 18 and the active layer 20, and a p-Al _W Ga _1-W As optical guide layer 36 is provided between the second cladding layer 22 and the active layer 20.
These guide layers 34, 36, the active layer 20, the cladding layers 18, 22, the current confinement layers 30, 32, and the optical reflector 24,
26, a Fabry-Perot resonator type semiconductor laser 38
Therefore, the optical resonator 10 is configured.

These optical guide layers 34 and 36 are provided in stripes by extending in the optical waveguide direction P, and the first cladding layer 1
The light guide layer 34, the active layer 20, the light guide layer 36, and the second cladding layer 22 are sequentially provided on the substrate 8. One side of each of the striped layers 18, 34, 20, 36 and 22 is embedded with the current confinement layer 30, and the other side of each of the striped layers 18, 34, 20, 36 and 22 is filled with a current. The narrowing layer 32 is embedded. Further, the grating 12 is provided at the interface between the second cladding layer 22 and the light guide layer 36.

FIG. 6 is a sectional view schematically showing the structure of the third embodiment of the present invention, showing a section taken along the optical waveguide direction P. In FIG. Hereinafter, differences from the first embodiment will be mainly described, and detailed description of the same points as the first embodiment will be omitted.

In this embodiment, the optical resonator 10 is the semiconductor laser 38. The structure and forming material of the semiconductor laser 38 can be variously changed, but here, as an example, the semiconductor laser 38 is a Bragg reflector type semiconductor laser, and the semiconductor laser 38 is configured as follows, for example. That is,
The light reflector 24 is used as the cleavage plane 40 and the light reflector 26 is used as the grating 44, and the light reflectors 24 and 26, the active layer 20, the cladding layers 18 and 22, and the current confinement layers 30 and 32 are used.
Thus, a Bragg reflector type semiconductor laser 38 is constructed.

The light reflector 26 has concave portions 44a and convex portions 44b provided alternately along the optical waveguide direction P, and the arrangement cycle of the concave portions 44a and the convex portions 44b selectively selects pump light of frequency f _3. Designed to reflect on. This light reflector 2
6 is provided at the interface between the active layer 20 and the second cladding layer 22. In the figure, the total length of the light reflector 26 in the light guiding direction P is indicated by reference character L _R.

FIG. 7 is a sectional view schematically showing the structure of the fourth embodiment of the present invention, showing a section taken along the optical waveguide direction P. As shown in FIG. Hereinafter, differences from the first embodiment will be mainly described, and detailed description of the same points as the first embodiment will be omitted.

In this embodiment, the optical resonator 10 includes a semiconductor laser 38 having an active layer 20, an optical fiber 46 having an input / output end 46a optically coupled to one end of the active layer 20, and an input / output. It has one optical reflector 24 provided on the optical fiber 46 near the end 46a and the other optical reflector 26 provided on the other end of the active layer 20. One of the light reflectors 24 is a diffraction grating 48 that reflects pump light.

Here, the semiconductor laser 38 is assumed to be a Fabry-Perot resonator type semiconductor laser configured similarly to the first embodiment. Then, the active layer 20 on which the cleavage plane 40 is formed
Antireflection film 5 on one end
0 is provided to prevent light reflection on the cleavage plane 40. The input / output end 46a of the optical fiber 46 is optically coupled to one end of the active layer 20 through the antireflection film 50.

The optical fiber 46 has a clad 46b and a core 46c embedded in the clad 46b. The method of forming one of the optical reflectors 24 provided on the optical fiber 46 is not limited, but, for example, the literature: IEICE Technical Report O
PE94-5 p25-30 As disclosed in May 1994, the core 46c to which Ge is added is irradiated with ultraviolet rays to form a periodic refractive index change in the core 46c. Diffraction grating 4 consisting of this periodic refractive index change
8 is a light reflector 24, and the cycle of the change in the refractive index is designed to selectively reflect the pump light having the frequency f ₃ . The cleaved surface 42 formed at the other end of the active layer 20 of the semiconductor laser 38 is used as the other optical reflector 26.

The optical fiber 4 on the side opposite to the input / output end 46a
An end portion (not shown) of 6 is optically coupled to the next-stage optical component, and the frequency-converted light of frequency f ₁ emitted from the optical resonator 10 is transmitted to the next-stage optical component via the optical fiber 46. Incident.
At this time, in order to prevent the pump light from entering the optical component of the next stage as noise, the reflectance of the other light reflector 26 with respect to the pump light is set to the reflectance of the one light reflector 24 with respect to the pump light. Therefore, the pump light is emitted from the other light reflector 26 to the outside of the active layer 20. Further, in order to prevent the input signal light from entering the optical component of the next stage by the optical filter 52, the optical filter 52 which does not transmit the input signal light of the frequency f _{1 is provided at} the input / output end 46a.
It is provided on the optical fiber 46 in the vicinity.

Here, the optical filter 52 is a diffraction grating 54 that reflects the input signal light of frequency f ₁ . Diffraction grating 54
Are formed in the same manner as the diffraction grating 48 described above, and the period of the change in the refractive index of the diffraction grating 54 is designed to selectively reflect the input signal light of the frequency f ₁ . And the active layer 2
One optical resonator 24 and one optical filter 5 are sequentially arranged from the 0 side.
2 is provided. The optical filter 5 is sequentially arranged from the side of the active layer 20.
Two or one optical resonator 24 (48) may be provided.

In this embodiment, a current is injected into the active layer 20 to generate pump light in the active layer 20, and the pump light is oscillated by reciprocating between the light reflectors 24 and 26. The pump light of frequency f ₃ is lased and the input signal light of frequency f ₂ is incident on the active layer 20, and the frequency conversion light of frequency f ₁ is generated in the active layer 20 by the difference frequency mixing. This frequency-converted light is made into signal light and enters the next stage optical component through the optical fiber 46. Here, f ₁ = f ₃ −f ₂ (f ₃ > f ₂ ) can be expressed, and if the wavelengths of the pump light, the input signal light, and the frequency conversion light are λ ₃ , λ _2, and λ ₁ , respectively, 1 / λ ₁ = 1 / λ
It can be expressed as ₃ −1 / λ ₂ .

In this embodiment, the reflectance of the other light reflector 26 with respect to the pump light is set to be smaller than the reflectance of the one light reflector 24 with respect to the pump light, and the one light reflector 24 is connected to the optical fiber 46. It is possible to prevent the pump light from becoming noise and entering the next-stage optical component because it is provided in the optical component.

An optical filter 5 which does not transmit the input signal light
Since No. 2 is provided in the optical fiber 46, it is possible to prevent the input signal light from entering the optical component of the next stage as noise.

Further, since the one optical reflector 24 and the optical filter 52 are the diffraction gratings formed on the optical fiber 46, the optical axis alignment between the optical reflector 24, the optical filter 52 and the optical fiber 46 becomes unnecessary. .

The present invention is not limited to the above-mentioned embodiment, but the shape, constitution, size, shape, disposition position, forming material, conductivity type, composition and other conditions of each constituent component can be arbitrarily set. Can be changed.

For example, in the above embodiment, AlGaAs
Although the example in which the system semiconductor material is used as the material for forming the semiconductor laser, in particular, the optical resonator has been described, various compound semiconductors having a nonlinear optical effect can be used as the other material. For example, an InGaPAs-based semiconductor material may be used. In this case, the substrate 28 is an n-GaAs substrate, the first cladding layer 18 is an n-In _X Ga _1-X P layer, and the active layer 20.
N or _{p-In X Ga 1-X} P Y As 1-Y layer (where, X
> Y), the current confinement layer 30,32 In _V Ga _1-V P layer,
Also, the second cladding layer 22 may be a p-In _x Ga ₁ -xp layer. Further, the conductivity type can be arbitrarily changed, for example, the conductivity type may be opposite conductivity type or the active layer may be non-doped.

Further, the arrangement position of the grating 12 can be changed arbitrarily and suitably. For example, in the embodiment of FIG. 1, the grating 12 is replaced by the substrate 28 and the first cladding layer 1.
You may make it provide in the interface of 8. In the embodiment of FIG. 4, the grating 12 is provided at the interface between the first cladding layer 18 and the optical guide layer 34 and the optical guide layer 36 is not provided, or the grating 12 is provided at the second cladding layer 22 and the optical guide layer 36. The light guide layer 34 may be provided at the interface and not provided.

In addition, the grating 12 for phase matching is
It may be provided over the entire optical resonator 10 along the optical waveguide direction P, or may be provided only on a part of the optical resonator 10 along the optical waveguide direction P.

[0053]

As is apparent from the above description, according to the optical frequency conversion element of the present invention, the pump light is oscillated in the optical resonator, so that the pump light can be input to the optical resonator. Operations such as optical axis alignment can be omitted. Further, it is not necessary to separately prepare a light source for pump light.

Moreover, since the optical resonator is provided with the grating to form the first and second regions, it is possible to obtain frequency-converted light having a practically sufficient optical output intensity.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing the configuration of a first embodiment of the present invention.

FIG. 2 is a sectional view schematically showing the configuration of the first embodiment of the present invention.

FIG. 3 is a diagram showing the relationship between the total length L of the phase matching grating and the optical power density of frequency converted light.

FIG. 4 is a sectional view schematically showing the configuration of a second embodiment of the present invention.

FIG. 5 is a sectional view schematically showing the configuration of a second embodiment of the present invention.

FIG. 6 is a sectional view schematically showing the configuration of a third embodiment of the present invention.

FIG. 7 is a cross sectional view schematically showing a configuration of a fourth embodiment of the present invention.

[Explanation of symbols]

 10: Optical resonator 12: Grating 12a: Recessed portion 12b: Convex portion 14: First region 16: Second region

Claims (9)

[Claims] 1. An optical resonator for inputting signal light and for oscillating pump light for frequency conversion of the input signal light, and a phase matching grating provided in the optical resonator, The grating has concave portions and convex portions provided alternately and periodically in the optical waveguide direction, and the concave portions form a first region having _a first propagation constant difference Δk _a represented by the following equation (a), An optical frequency conversion element, wherein the convex portion forms a second region having a second propagation constant difference Δk _b represented by the following equation (b). _{Δk a · l a = s ·} π ...... (a) _{where, Δk a = k 3a -k 2a} -k 1a, s is an odd number (s = 1,
3,5, ......) k _3a: first propagation constant of the pump light in the region k _2a: first input signal light in the region propagation constant k _1a: propagation constant l _a frequency converted light in the first region : length of the first region in the optical waveguide direction _{Δk b · l b = s ·} π ...... (b) _{where, Δk b = k 3b -k 2b} -k 1b k 3b: the pump light in the second region propagation constant k _2b: the length of the second region in the optical waveguide direction: second propagation constant k _1b of the input signal light in the region of: propagation constant l _b of the frequency-converted light in the second region 2. The optical frequency conversion element according to claim 1, wherein the absorption edge frequency of the optical resonator is made higher than the frequency of the input signal light and the frequency of the frequency conversion light. 3. The optical frequency conversion element according to claim 1, wherein the laser oscillation frequency of the optical resonator is higher than the frequency of the input signal light and the frequency of the frequency conversion light. 4. The optical frequency conversion element according to claim 1, wherein the optical resonator is a Fabry-Perot resonator type or Bragg reflector type semiconductor laser. 5. The optical frequency conversion element according to claim 1, wherein the optical resonator includes a semiconductor laser having an active layer, and an optical fiber having an input / output end optically coupled to one end of the active layer. , Having one optical reflector provided on the optical fiber near the input / output end and the other optical reflector provided on the other end of the active layer, and pumping light on the one optical reflector. An optical frequency conversion element characterized by being formed as a reflective diffraction grating. 6. The optical frequency conversion element according to claim 5, wherein the reflectance of the other optical reflector with respect to the pump light is smaller than the reflectance of the one optical reflector with respect to the pump light. Frequency conversion element. 7. The optical frequency conversion element according to claim 5, wherein an optical filter is provided in the optical fiber near the input / output end, and the optical filter is a diffraction grating that reflects input signal light. Conversion element. 8. The optical frequency conversion element according to claim 7, wherein one optical resonator and one optical filter are sequentially provided from the active layer side. 9. The optical frequency conversion element according to claim 5, wherein an antireflection film is provided at one end of the active layer, and an input / output end of the optical fiber is provided at one end of the active layer through the antireflection film. An optical frequency conversion element characterized by being optically coupled to a section.