JP3029771B2 - Optical frequency conversion element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Hitherto, 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 or a method disclosed in Japanese Patent Application Laid-Open No. 2-68528.

In four-wave mixing, a current equal to or less than an oscillation threshold is injected into an optical resonator of a semiconductor laser to amplify light in the optical resonator. Thereby, the efficiency of frequency conversion is increased. At the same time, the signal light having the frequency F ₁ and the pump light (F ₁ <F ₂ ) having the frequency F ₂ are individually generated by a light source 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 −
Vibrating at F _1, this vibration, the input signal light and the pumping light is modulated. As a result, the frequency F ₁ − (F ₂ −F
₁ ) and frequency-converted light of F ₂ + (F ₂ −F ₁ ) is generated.

[0004] 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 light can be amplified.

[0005]

However, in the above-described conventional optical frequency conversion, light sources for signal light and pump light are separately provided outside the optical resonator, and light generated by these light sources is supplied to the optical resonator. Input into the active layer to be configured. 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 operation of inputting both the signal light and the pump light to the active layer is a difficult operation.

In the above-described conventional optical frequency conversion, frequency-converted light is generated by oscillation of the number of electron carriers, so that 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 device which utilizes a semiconductor laser as a nonlinear 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 increase the variable range of the optical frequency in an optical frequency conversion element in which a semiconductor laser is used as a nonlinear optical medium and also used as a pump light source. is there.

A third object of the present invention is to provide an optical frequency conversion device in which a semiconductor laser is used as a non-linear optical medium and also used as a pump light source, wherein the pump light and / or the input signal light become noise light. An object is to prevent output to the next-stage optical component.

[0010]

In order to achieve the first object, an optical frequency conversion element according to the present invention receives a signal light and outputs a pump light for frequency conversion of the input signal light by laser oscillation. And a grating for phase matching provided in the optical resonator. The grating has concave portions and convex portions provided alternately and periodically in the optical waveguide direction. a) forming a first region having _a first propagation constant difference Δk _a expressed by the following equation (b):
forming a second region having a k _b and characterized by comprising.

Δk _a · l _a = s · π (a) where Δk _a = k _3a −k _2a −k _1a , and s is an odd number (s = 1,
3, 5,...) K _3a : propagation constant of pump light in the first region k _2a : propagation constant of input signal light in the first region k _1a : propagation constant of frequency-converted light in the first region l _a : 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]

SUMMARY OF] According to this configuration, laser oscillation of the pump light frequency f ₃ within the optical resonator. This generates a signal light of a frequency f ₂ in the optical resonator outside of the light source with inputs the signal light in the optical resonator. As a result, the difference frequency mixing of the pump light frequency f ₃ and the frequency f ₂ of the signal light, the frequency-converted light of a frequency _{f 1 (f 1 = f 3} -f 2, f 3> f
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 in the optical resonator. Moreover, the first region is _{Δk a · l a = s ·} π
Has a first propagation constant difference .DELTA.k _a represented in a second region Δk _b · l _b = s · second propagation constant difference represented by [pi delta
with a k _b. Therefore, the first and second regions cause a phase shift (phase difference) between the pump light, the input signal light, and the frequency-converted light.
Since the phase difference can be compensated so that the phase difference between d Wave and Free Wave is 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. The drawings are only schematically shown to the extent that the invention can be understood, and thus 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 FIG. 1, the optical frequency conversion device of this embodiment includes an optical resonator 10 which receives a signal light and oscillates a 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 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 Δka represented by the following equation (a). 14, and the convex portion 12b has a second propagation constant difference Δ represented by the following equation (b).
forming a second region 16 having a k _b.

Δk _a · l _a = s · π (a) where Δk _a = k _3a −k _2a −k _1a , and s is an odd number (s = 1,
3,5, ......) k _3a: first propagation of the pump light in the region 14 constant k _2a: first propagation constant of the input signal light in the region 14 k _1a: propagation of the 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 optical resonator 10 is provided with a first cladding layer 18, an active layer 20 and a second cladding layer 22 sequentially provided on the cladding layer 18, and one end of the active layer 20. The other provided on the side of the other end of the light reflector 24 and the active layer 20 And at least a light reflector 26.

When the pump light, the input signal light, and the frequency-converted light are guided in the optical resonator 10, the optical waveguide region is mainly the active layer 20. The first region 14 is a region corresponding to the grating concave portion 12a in the optical waveguide region, and the second region 16 is a region corresponding to the grating convex portion 12b in the optical waveguide region. The optical waveguide direction P is a direction 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 the 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 material forming each element constituting the optical resonator 10 and the depth D of the grating 12 (see FIG. 1).
Thus, for example, by arbitrarily selecting suitably the forming material and the depth D of each element constituting the optical resonator 10, it is possible to obtain a desired propagation constant difference .DELTA.k _a and .DELTA.k _b.

[0020] The length of the recess 12a of the grating 12 the length of l _a and the convex portion 12b is a l _b, provided alternately along the recesses 12a and the projections 12b into the optical waveguide direction P.

If the first and second regions 14 and 16 formed by the adjacent concave portions 12a and convex portions 12b are phase matching regions for one cycle, the pump light, the signal light, and the frequency-converted light can be used for one cycle. In addition, by passing through the phase matching regions 14 and 16 for each other, a band wave (Bound 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.
As described above, 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, frequency-converted light having a light output intensity that is practically satisfactory can be obtained. For example, s = 1.

When the grating 12 is not provided, more specifically, the phase difference between the band wave (Bound Wave) and the free wave (Free Wave) is more specific than the phase difference between the pump light, the input signal light, and the frequency converted light. It is easy to deviate from 2 · s · π. As a result, it is difficult to obtain frequency-converted light having an optical output intensity sufficient for practical use due to a phase shift. In order to solve 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 constant,
The design conditions may be determined so as to satisfy the equations (a) and (b). Design conditions, for example, the effective refractive index of the first and second regions 14 and 16, the depth D of the recess 12a length l _a and the convex portion 12b of the grating 12 the length l _b.

When frequency conversion of the input signal light is performed, the pump light having the frequency f ₃ is oscillated by the laser in the optical resonator 10. This generates a signal light of a frequency f ₂ in the optical resonator 10 outside of the light source (not shown) with, inputting the signal light in the optical resonator. Then, frequency-converted light (f ₁ = f ₃ −f ₂ , f ₃ > f ₂ ) of the frequency f ₁ 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 of the absorption edge of the optical resonator 10, particularly the frequency of the absorption edge of the active layer 20, is changed to the frequency f of the input signal light.
Preferably ₂ and greater than the frequency f ₁ of the frequency converted light. 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.

By setting 1) or 2), the optical resonator 1
The optical waveguide region of zero can be made substantially transparent to light of frequencies f ₂ and f ₁ , and thus the dispersion of the refractive index in the optical waveguide region of the optical resonator 10 can be reduced by the frequencies f ₂ and f _1. Light can be made very small. If laser oscillation is performed so that the frequency f ₃ of the pump light is kept almost constant at the design value while the dispersion of the refractive index is extremely small, the first frequency f ₂ of the input signal light can be shifted from the design value. And (a) and (b) in the second regions 14 and 16
Can be approximately satisfied.

For example, s = 1. The design values of the frequency f ₁ of the frequency f ₂ and the frequency-converted light of the input signal light, the value be preferable in the state of the 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. Here is the wavelength of the input signal light _{λ 2 (= c / f 2} ), the wavelength of the pump light λ ₃ (= c /
f ₃ ) is approximately twice as large. In this case, the equations (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 range of the design value ± 50 nm. it can, therefore it is possible to change the frequency f ₁ of the frequency converted light in wider range than the prior art.

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

In this embodiment, the optical resonator 10 is a semiconductor laser 38. Although the structure and the forming material of the semiconductor laser 38 can be variously changed, here, as an example, the semiconductor laser 38 is a Fabry-Perot cavity semiconductor laser,
For example, the semiconductor laser 38 is configured 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
a _1-x As second cladding layer 22 is provided. Each of these layers 1
Each of the layers 8, 20, and 22 is extended in a stripe shape in the optical waveguide direction P, and one side of each of the layers 18, 20, and 22 is filled with the current confinement layer 30 and the other side is filled with the 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. Also, cleavage planes 40 and 4 are provided at one and the other end of the active layer 20.
2 and these cleavage planes 40 and 42 are
Light reflectors 24 and 26. In this case, the Fabry-Perot cavity semiconductor laser 38 and thus the optical resonator 10 are:
Active layer 20, cladding layers 18, 22, current confinement layer 30,
32 and light reflectors 24, 26.

The 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.
It is provided at the interface between the first and second cladding layers 22.

With respect to the optical frequency conversion element having the structure shown in FIGS. 1 and 2 described above, 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. 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 overall length L [m
m], the optical power density [kW / cm ² ] of the frequency-converted light was determined.

The wavelength λ ₃ (= c / f ₃ ) of the pump light: 0.8 μm The power density P _{3 of the} pump light: 10 ⁸ W / cm ² The wavelength λ ₂ (= c / f ₂ ) of the input signal light: 1 .65 μm Power density of input signal light P ₂ : 10 ⁶ W / cm ² Wavelength λ ₁ (= c / f ₁ ) of frequency converted light: 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 Nonlinear optical constant of 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 for 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 and 22 for pump light: 3 .
265 Refractive Index of Cladding Layers 18, 22 for Input Signal Light:
3.258 Refractive index of cladding layers 18 and 22 for frequency-converted light:
3.461 length of the first region 14 l _a: 1.45 .mu.m Length l _b of the second region 16: sectional area of 1.85μm waveguide active layer 20 in a direction perpendicular to the direction P: 1 [mu] m ² FIG. As can be understood from FIG. 3, the output intensity of the frequency-converted light increases as the total length L increases. Under the above-described conditions, for example, by setting the total length L to 0.4 mm and inputting an input signal light with an optical power of 1 mW,
It is possible to obtain frequency-converted light having an optical power of the order, and thus to obtain frequency-converted light having practically sufficient optical power.

FIGS. 4 and 5 are sectional views schematically showing the structure of the second embodiment of the present invention. 4 shows a cross section taken along the optical waveguide direction P through the active layer 20, and FIG.
2 shows a cross section taken along line VV in FIG.
Hereinafter, mainly the differences from the first embodiment will be described,
Detailed description of the same points as in the first embodiment will be omitted.

In this embodiment, n-Al _W Ga _{1 -W} As
A light 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 light guide layer 36 is provided between the second cladding layer 22 and the active layer 20,
These guide layers 34, 36, active layer 20, cladding layers 18, 22, current confinement layers 30, 32 and light reflector 24,
26, a Fabry-Perot cavity semiconductor laser 38
Therefore, the optical resonator 10 is configured.

The light guide layers 34 and 36 are provided in a stripe shape so as to extend in the optical waveguide direction P.
The light guide layer 34, the active layer 20, the light guide layer 36, and the second cladding layer 22 are sequentially provided on 8. One side of each of the striped layers 18, 34, 20, 36 and 22 is filled with a 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. It is embedded with the constriction layer 32. 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 configuration of the third embodiment of the present invention, and shows a section taken along the optical waveguide direction P. Hereinafter, points different 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 a semiconductor laser 38. Although the structure and the material of the semiconductor laser 38 can be variously changed, 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 a cleavage plane 40 and the light reflector 26 is a grating 44. 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 formed.

The light reflector 26 has concave portions 44a and convex portions 44b provided alternately along the optical waveguide direction P, and the arrangement period of these concave portions 44a and convex portions 44b is such that pump light having a frequency f ₃ is selectively provided. Design to reflect light. 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 length of the optical reflector 26 in the optical waveguide direction P, shown by reference numeral L _R.

FIG. 7 is a sectional view schematically showing the structure of the fourth embodiment of the present invention, and shows a section taken along the optical waveguide direction P. Hereinafter, points different 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 comprises: 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; It has one light reflector 24 provided on the optical fiber 46 near the end 46a and the other light 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 the pump light.

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

The optical fiber 46 has a cladding 46b and a core 46c embedded in the cladding 46b. The method of forming one of the optical reflectors 24 provided on the optical fiber 46 is not limited. For example, the document: Technical report O of the Institute of Electronics, Information and Communication Engineers 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 was a light reflector 24, designing period of the refractive index change to selectively reflect pump light frequency f _3. The cleavage plane 42 formed at the other end of the active layer 20 of the semiconductor laser 38 is used as the other light reflector 26.

The optical fiber 4 on the side opposite to the input / output end 46a
6 is optically coupled to the next-stage optical component, and the frequency-converted light having the 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, the reflectance of the other light reflector 26 with respect to the pump light is changed to the reflectance of the one light reflector 24 with respect to the pump light in order to prevent the pump light from entering the next-stage optical component as noise. And the pump light is emitted from the other light reflector 26 to the outside of the active layer 20. Further, since the input signal light by the optical filter 52 is prevented from entering the next stage of the optical components, the optical filter 52 does not transmit an input signal light of a frequency f _2, input and output end 46a
It is provided on a nearby optical fiber 46.

Here, the optical filter 52 is a diffraction grating 54 that reflects the input signal light having the frequency f ₂ . Diffraction grating 54
And it was formed in the same manner as the diffraction grating 48 as described above, to design the period of refractive index change of the diffraction grating 54 so as to selectively reflect an input signal light of a frequency f _2. And the active layer 2
0, one of the optical resonator 24 and the optical filter 5
2 is provided. The optical filter 5 is sequentially arranged from the active layer 20 side.
Two or one of the optical resonators 24 (48) may be provided.

In this embodiment, a current is injected into the active layer 20, a pump light is generated in the active layer 20, and the pump light is caused to reciprocate between the light reflectors 24 and 26 to cause laser oscillation. A pump light having a frequency f ₃ is oscillated by laser, and an input signal light having a frequency f ₂ is incident on the active layer 20, and frequency-converted light having a frequency f ₁ is generated in the active layer 20 by difference frequency mixing. This frequency-converted light is incident on the next-stage optical component via the optical fiber 46 as signal light. Here, f ₁ = f ₃ −f ₂ (f ₃ > f ₂ ), and if the wavelengths of the pump light, the input signal light, and the frequency-converted light are λ ₃ , λ _2, and λ ₁ , respectively, 1 / λ ₁ = 1 / λ
₃ -1 / _{λ 2} and expressed.

In this embodiment, the reflectance of the other light reflector 26 with respect to the pump light is made smaller than the reflectance of the one light reflector 24 with respect to the pump light. Therefore, it is possible to prevent the pump light from becoming noise and entering the next-stage optical component.

An optical filter 5 that does not transmit the input signal light
Since the optical fiber 46 is provided in the optical fiber 46, it is possible to prevent the input signal light from becoming noise and entering the next optical component.

Further, since one of the optical reflector 24 and the optical filter 52 is a diffraction grating 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 only to the above-described embodiment, and the shape, structure, dimensions, shape, arrangement position, forming material, conductivity type, composition, and other conditions of each component can be arbitrarily and suitably set. Can be changed.

For example, in the above-described embodiment, AlGaAs
Although an example has been described in which the system semiconductor material is used as a material for forming a semiconductor laser, particularly an optical resonator, various compound semiconductors having a nonlinear optical effect can be used as 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 is
To an n- or p-In _x Ga _1-x P _Y As _1-Y layer (where X
> Y), the current confinement layers 30 and 32 are formed of In _V Ga _1- VP layers,
And, a second clad layer 22 may be a _{p-In X Ga 1-X} P layer. The conductivity type can be arbitrarily and suitably changed. For example, the conductivity type may be set to the opposite conductivity type, or the active layer may be made non-doped.

The position of the grating 12 can be arbitrarily changed. For example, in the embodiment shown in FIG.
8 may be provided at the interface. In the embodiment shown in FIG. 4, the grating 12 is provided at the interface between the first cladding layer 18 and the light guide layer 34 and the light guide layer 36 is not provided. The light guide layer 34 may not be provided at the interface.

The grating 12 for phase matching is
In addition to being provided over the entire optical resonator 10 along the optical waveguide direction P, it may be provided on only 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 device of the present invention, the pump light is oscillated by the laser in the optical resonator, so that the pump light is input to the optical resonator. Operations such as optical axis alignment can be omitted. Also, there is no need to separately prepare a pump light source.

Moreover, since the first and second regions are formed by providing a grating in the optical resonator, frequency-converted light having a practically sufficient light output intensity can be obtained.

[Brief description of the drawings]

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

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

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

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

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

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

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

[Explanation of symbols]

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

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-296729 (JP, A) Spring 1993 40th Joint Lecture on Applied Physics Lectures, 3rd volume, 29p-Y-15 (58) Field (Int.Cl. ⁷ , DB name) G02F 1/377 H01S 3/108 JICST file (JOIS)

Claims (9)

(57) [Claims] An optical resonator that receives a signal light and oscillates a pump light for laser conversion of a frequency of the input signal light, and a grating for phase matching 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 Δka represented by the following equation (a): the convex portion is expressed by the following equation (b) a second optical frequency conversion element characterized by comprising forming a second region having a propagation constant difference .DELTA.k _b of represented by. _{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 : propagation constant of pump light in the first region k _2a : propagation constant of input signal light in the first region k _1a : propagation constant of frequency-converted light in the first region l _a : 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 device according to claim 1, wherein the absorption edge frequency of the optical resonator is higher than the frequency of the input signal light and the frequency of the frequency conversion light. 3. The optical frequency conversion device 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 device according to claim 1, wherein the optical resonator is a Fabry-Perot resonator type semiconductor laser or a Bragg reflector type semiconductor laser. 5. The optical frequency conversion device according to claim 1, wherein the optical resonator comprises: 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. A light reflector provided on the optical fiber near the input / output end, and another light reflector provided on the other end of the active layer, wherein the one light reflector is provided with pump light. An optical frequency conversion element, which is configured as a reflection diffraction grating. 6. The optical frequency conversion device according to claim 5, wherein the reflectance of the other light reflector for the pump light is smaller than the reflectance of the one light reflector for the pump light. Frequency conversion element. 7. The optical frequency conversion device according to claim 5, wherein an optical filter is provided on the optical fiber near the input / output end, and the optical filter is formed as a diffraction grating for reflecting input signal light. Conversion element. 8. The optical frequency conversion device according to claim 7, wherein one of the optical resonator and the optical filter is provided sequentially from the active layer side. 9. The optical frequency conversion device according to claim 5, wherein an antireflection film is provided at one end of the active layer, and the input / output end of the optical fiber is connected to one end of the active layer via the antireflection film. An optical frequency conversion element, which is optically coupled to a part.