JP3424698B2 - Garnet crystal waveguide with amplifying action - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a garnet crystal waveguide,
The present invention relates to a structure of a garnet crystal waveguide that efficiently amplifies light having a wavelength of around 1.6 μm.

[0002]

2. Description of the Prior Art As an optical amplifier in the wavelength range of 1.6 μm, expectations are high for a practical, durable device that is compact, inexpensive, and easily connectable to other waveguide components. . Light in the 1.6 μm wavelength range has a propagation loss of 1.
Since it is slightly larger than 5 μm light, it is more likely to be used for maintenance of the optical communication line rather than being used for communication itself. Light in the wavelength range of 1.6 μm can be transmitted through the optical communication line without competing with light in the communication wavelength range, and whether or not the line is functioning normally by using this kind of optical signal. That is, work for maintenance is performed.

Light in the wavelength range of 1.5 μm, which has a low propagation loss, is mainly used for optical communication. In high-speed, large-capacity communication, it is important to directly amplify the signal light whose intensity has decreased and propagated over a certain distance to eliminate time delay. In the wavelength region of 1.5 μm, an optical amplifier (Erbium Doped Fiber A) using a silica glass fiber to which a small amount of erbium, which is a rare earth element, is added.
mplifier (EDFA) is used to directly amplify the signal light.

[0004]

Although the light in the wavelength range of 1.6 μm, which has a high possibility of being mainly used for line maintenance, a certain level of signal light intensity is required for accurate maintenance. Therefore, it is similar to the light in the communication wavelength range that there is a high need to directly amplify the light in this wavelength range. However, so far, no optical amplification capable of directly amplifying light in the wavelength range of 1.6 μm has been developed. The reason is as follows.

First, even if a silica glass fiber is used as the host material of the amplification medium, 1.6 μ in quartz is used.
No active ion emitting in the m wavelength region has been reported. Therefore, it is possible to use an optical crystal as the host material. Up to now, by using the fluorescence as in the case of amplification by constructing a resonator by using the end face of the crystal as a mirror, 1.
Yttrium aluminum garnet (YAG), gadolinium gallium garnet (GGG), in which tetravalent ions of holmium, erbium, nickel and chromium are added as active ions to those that have been or have the potential to operate as solid-state lasers in the 6 μm wavelength range, Examples include lithium niobate and yttrium aluminate. They are,
The electrons of the active ions arranged in the crystal emit light with high efficiency due to the action of the crystal field, so that light is amplified with a sufficiently short length as compared with the fiber type amplifier. However, when holmium or erbium is selected as the active ion, YAG
When crystals or yttrium aluminate are used as the host, the central wavelength of fluorescence exists in the wavelength range of 1.6 μm, but it acts only in a very narrow wavelength range. In the case of nickel ions, light emission at room temperature cannot be realized. Even if a quaternary chromium ion is selected, only a small part has a large propagation loss and the valence of the chrome ion can be made tetravalent, and most of the chromium ions remain trivalent. Selecting the other optical crystal material as the host material and setting the central wavelength to the 1.6 μm wavelength range,
Although not impossible, it is difficult to control the refractive index and it is difficult to realize a waveguide structure that enables single mode operation. In addition, even if a garnet crystal other than YAG is selected as a host and an attempt is made to emit light by the ⁴ I _13/2 → ⁴ I _15/2 transition of erbium, it can not be realized by using other than aluminum garnet, and the center wavelength is 1.645 μm. However, it is the same that the bandwidth that can be amplified is narrow.

As described above, in the conventional technique, 1.6 μm
It has been difficult to realize a waveguide element that operates in a single mode and that can be easily connected to another waveguide type component as the amplification width in the wavelength region and that is small and inexpensive.

An object of the present invention is to solve the above problems by appropriately selecting a substrate material, a clad material and a core material, which makes it possible to pump with an inexpensive 0.81 μm semiconductor laser. As an amplifier in the wavelength range,
It is an object of the present invention to provide a garnet crystal waveguide having an amplifying function, which is small-sized, inexpensive, and easily connectable to other waveguide-type components, and which functions as a waveguide element that can be practically used.

[0008]

In order to achieve such an object, the garnet crystal waveguide according to the present invention is provided on a substrate.
Formed on the lower clad layer and on the lower clad layer
Has a larger refractive index than the lower cladding layer
Core layer processed into a dice, the core layer and the clad
An upper layer having a smaller refractive index than the core layer formed on the layer.
A garnet crystal waveguide comprising a dead layer, comprising:
The plate is a Gd ₃ Ga ₅ O ₁₂ (GGG) single crystal substrate,
The lower clad layer and the upper clad layer are made of Eu.
_2.94 La _0.06 Al _0.425 Ga _4.575 O
_And has a composition of ₁₂ and a lattice constant almost the same as that of the single crystal substrate.
A garnet crystal having Y, L
Contains a, Nd, Yb, Lu, Ho, Er, Tm, Mg
The substitution type GGG crystal film, wherein the core layer is 0.8
It absorbs the excitation light of 1 μm and is excited to the ⁴ F _5/2 level,
Nd ³⁺ ions that transition to the ⁴ F _3/2 level without light emission ,
The energy absorbed by the Nd ³⁺ is transferred to ² F
Active ions that are excited to the _5/2 level and are directly involved in light emission
³⁺ ions and Lu ⁴⁺ that transfer energy to
Ions and the above-mentioned active ions for energy transfer
After receiving and being excited to the ⁵ I ₆ level, it is non-emissive and is excited to the ⁵ I ₇ level.
Position, and induces light with signal light in the 1.6 μm wavelength range.
Ho ³⁺ ions and Er ⁴⁺ ions that emit and emit energy
After being excited to the ³ H ₅ level by receiving the Lugie transfer,
Transitions to ³ H ₄ level in a light, the signal light of 1.64μm wavelength band
³⁺ ions and stimulated emission of light by Yb
⁴⁺ ions, and ⁴ I after receiving energy transfer
After being excited to the _11/2 level, it emits ⁴ I _13/2 without emitting light.
Transitions to the level and emits light by the signal light in the wavelength range of 1.6 μm.
Er ³⁺ ions and Tm ⁴⁺ ions that are stimulated to be emitted
It is characterized by being provided . Also, another gar according to the present invention
The net crystal waveguide is formed on the substrate and the lower cladding
Layer and the lower cladding formed on the lower cladding layer.
Core layer with a higher refractive index than the core layer and processed into a ridge shape
And the core formed on the core layer and the clad layer
Layer consisting of an upper clad layer with a smaller refractive index than the layer
A preparative crystal waveguide, the substrate is _Gd 3 _Ga 5 _{O 12}
(GGG) single-crystal substrate, the lower clad layer and the
And the upper clad layer are made of Eu _2.84 La _0.16 A.
The single crystal substrate having a composition of _0.6 Ga _4.4 O _12.
Is a garnet crystal having substantially the same lattice constant as
The core layer is made of Y, La, Nd, Yb, Dy, Ho, E.
A substitution type GGG crystal film containing r, Tm and Ti,
The core layer absorbs 0.81 μm of excitation light and absorbs ⁴ F.
Excited to the _5/2 level, non-luminous transition to the ⁴ F _3/2 level
Nd ³⁺ ions and the energy absorbed by the Nd ³⁺
It is excited to the ² F _5/2 level by the transmission of _energy and emits light.
Yb that transfers energy to active ions that are directly involved
³⁺ ion and Lu ⁴⁺ ion and the active ion
Yes, it is excited by energy transfer to the ⁵ I ₆ level.
After that, it transits to the ⁵ I ₇ level without emitting light, and has a wavelength of 1.6 μm.
Dy ²⁺ ions and stimulated emission of light by signal light in the region
And ^{Ho 3+} ions, undergoing energy transfer ³ H ₅ level
After being excited to the ³ position, it transitions to the ³ H ₄ level without light emission ,
Light is stimulated and emitted by signal light in the wavelength range of 1.64 μm
Tm ³⁺ and Er ²⁺ ions, and energy
_-After being transmitted and excited to the ⁴ I _11/2 level,
The light transitions to the ⁴ I _13/2 level and emits light in the 1.6 μm wavelength range.
Er ³⁺ ions that stimulate and emit light by signal light, and
Ho ²⁺ ions are provided. further,
The garnet crystal waveguide according to the present invention is formed on a substrate.
Formed on the lower clad layer and the lower clad layer.
The refractive index is larger than that of the lower clad layer and is applied like a ridge.
A core layer that has been machined and that is formed on the core layer and the clad layer.
An upper clad layer made of a material having a smaller refractive index than the core layer
A garnet crystal waveguide comprising:
₃ Ga ₅ O ₁₂ (GGG) is a single crystal substrate, the lower
The cladding layer and the upper cladding layer are made of Eu _2.94.
Set of La _0.06 Al _0.425 Ga _4.575 O ₁₂
And has substantially the same lattice constant as the single crystal substrate
Garnet crystal, wherein the core layer is Y, La, Nd,
Containing Yb, Lu, Ho, Er, Tm, Ca, Sr,
It is a substitution type GGG crystal film, and the core layer is 0.81 μm.
It absorbs the excitation light of m and is excited to the ⁴ F _5/2 level,
The Nd ³⁺ ion that transits to the ⁴ F _3/2 level by light,
² F due to the transfer of energy absorbed by Nd ³⁺
Active ions that are excited to the _5/2 level and are directly involved in light emission
³⁺ ions and Lu ⁴⁺ that transfer energy to
Ions and the above-mentioned active ions for energy transfer
After receiving and being excited to the ⁵ I ₆ level, it is non-emissive and is excited to the ⁵ I ₇ level.
Position, and induces light with signal light in the 1.6 μm wavelength range.
Ho ³⁺ ions and Er ⁴⁺ ions that emit and emit energy
After being excited to the ³ H ₅ level by receiving the Lugie transfer,
Transitions to ³ H ₄ level in a light, the signal light of 1.64μm wavelength band
³⁺ ions and stimulated emission of light by Yb
⁴⁺ ions, and ⁴ I after receiving energy transfer
After being excited to the _11/2 level, it emits ⁴ I _13/2 without emitting light.
Transitions to the level and emits light by the signal light in the wavelength range of 1.6 μm.
Er ³⁺ ions and Tm ⁴⁺ ions that are stimulated to be emitted
It is characterized by being provided. In addition, the fourth gas according to the present invention
The net crystal waveguide is formed on the substrate and
And a lower layer formed on the lower cladding layer.
Core layer processed into a ridge shape with a higher refractive index than the head layer
And the core formed on the core layer and the clad layer
Layer consisting of an upper clad layer with a smaller refractive index than the layer
A preparative crystal waveguide, the substrate is _Gd 3 _Ga 5 _{O 12}
(GGG) single-crystal substrate, the lower clad layer and the
And the upper clad layer are made of Eu _2.84 La _0.16 A.
The single crystal substrate having a composition of _0.6 Ga _4.4 O _12.
Is a garnet crystal having substantially the same lattice constant as
The core layer is made of Y, La, Nd, Yb, Ho, Er, T
A substitutional GGG crystal film containing m, Zr, Hf and Ge.
Yes, the core layer absorbs 0.81 μm excitation light
Excited to the ⁴ F _5/2 level and non-luminous to the ⁴ F _3/2 level
The transitioning Nd ³⁺ ion and the energy absorbed by the Nd ³⁺ are
Excited to the ² F _5/2 level by receiving energy transfer, and emitted
Y that transfers energy to active ions that are directly involved in light
b ³⁺ ion and Lu ⁴⁺ ion, and the active ion
Is excited by the energy transfer to the ⁵ I ₆ level.
After that, transition to ⁵ I ₇ level in a non-light emission, 1.6 [mu] m wave
Ho ³⁺ Io that stimulates and emits light by signal light in the long range
Was excited to the ³ H ₅ level by energy transfer .
Then, it transitions to the ³ H ₄ level without light emission, and the wavelength range of 1.64 μm
Of Tm ³⁺ ions that stimulate and emit light by the signal light of
And Er ²⁺ ions, and ⁴ I after energy transfer
After being excited to the _11/2 level, it emits ⁴ I _13/2 without emitting light.
Transitions to the level and emits light by the signal light in the wavelength range of 1.6 μm.
Er ³⁺ ions and Ho ²⁺ ions that are stimulated to be emitted
It is characterized by being provided. Furthermore, the fifth aspect of the present invention
The garnet crystal waveguide is formed on the substrate and is
And a lower layer formed on the lower cladding layer.
A core that has a higher refractive index than the rud layer and is processed into a ridge shape
A layer, and the core layer and the clad layer formed on the core layer.
Gane consisting of an upper clad layer with a smaller refractive index than the
And a substrate of Gd ₃ Ga ₅ O.
₁₂ (GGG) single crystal substrate, and the lower clad layer
And the upper clad layer is Eu _2.94 La
The composition of _0.06 Al _0.425 Ga _4.575 O ₁₂
A gar having substantially the same lattice constant as the single crystal substrate
The core layer is Y, La, Nd, Y
Contains b, Lu, Ho, Er, Tm, Mg, Ca, Zr
The substitution type GGG crystal film, wherein the core layer is 0.8
It absorbs the excitation light of 1 μm and is excited to the ⁴ F _5/2 level,
Nd ³⁺ ions that transition to the ⁴ F _3/2 level without light emission ,
The energy absorbed by the Nd ³⁺ is transferred to ² F
Active ions that are excited to the _5/2 level and are directly involved in light emission
³⁺ ions and Lu ⁴⁺ that transfer energy to
Ions and the above-mentioned active ions for energy transfer
After receiving and being excited to the ⁵ I ₆ level, it is non-emissive and is excited to the ⁵ I ₇ level.
Position, and induces light with signal light in the 1.6 μm wavelength range.
Ho ³⁺ ions and Er ⁴⁺ ions that emit and emit energy
After being excited to the ³ H ₅ level by receiving the Lugie transfer,
Transitions to ³ H ₄ level in a light, the signal light of 1.64μm wavelength band
To stimulated emission light by ^{Er 2+} ions, ^{Tm 3+} Lee
On and Yb ⁴⁺ ions, and receive energy transfer
Only in ⁴ I _11/2 after being excited level, ⁴ in the non-emission I
Transition to the _13/2 level and the signal light in the 1.6 μm wavelength range
Ho ²⁺ ion, Er ³⁺ ion that stimulates and emits light
And Tm ⁴⁺ ions.

The garnet crystal waveguide of the present invention has a structure whose conceptual diagram is shown in FIG.

Reference numeral 1 denotes a garnet single crystal substrate for forming an optical waveguide, which uses a gadolinium gallium garnet (GGG) single crystal substrate. 2 is the lower cladding, 3
Is an upper clad, has a lattice constant almost the same as that of the substrate material, and replaces at least a part of gadolinium with another rare earth element or yttrium, and replaces at least a part of gallium with aluminum. To use. Reference numeral 4 is a core for confining light and contains Nd, Dy, Ho, Er, Tm, and Y as rare earth elements.
b, containing several kinds of elements combined from Lu, adding at least one kind of element selected from Mg, Ca or Sr, and further selecting from Ti, Zr, Hf or Ge Garnet crystals to which one or more elements are added are used. A waveguide structure is realized by the composition ratio of aluminum and gallium in the clad and the core, and the active ions are Dy ²⁺ , Ho ²⁺ , Ho.
³⁺ , Er ²⁺ , Er ³⁺ , Er ⁴⁺ , Tm ³⁺ , Tm
Several kinds of appropriately selected from ⁴⁺ and Yb ⁴⁺ ions are used.

[0011]

The operation of the optical waveguide having the amplifying function of the present invention will be described as follows. Light from a very general 0.81 μm semiconductor laser made of AlGaAs is coupled to the core layer 4. Neodymium (N
d ³⁺ ) ions are present and absorb this light,
^The transition to ⁴ F _{5/2 occurs} , and the transition to the ⁴ F _3/2 level _occurs due to non-radiative transition. Further, the core layer 4 has a divalent thulium ion (Tm
²⁺ ), trivalent ytterbium ion (Yb ³⁺ ) and 4
There is a valent lutetium ion (Lu ⁴⁺ ), and due to the effect of interaction between electric dipoles, the energy absorbed by neodymium is entrusted to transfer to ² F _5/2 and transition to ² F _5/2 . The excited state is the same as that excited by light.
Energy-transferred Tm ²⁺ , Yb ³⁺ and Lu ⁴⁺
Similarly transfers energy to the active ions by the effect of the interaction between the electric dipoles. Finally, the above-mentioned active ions, which have received energy transfer, generate fluorescence after transitioning to each level of emission transition having a central wavelength in the 1.6 μm wavelength region by non-emission transition. Regarding this fluorescence, the emission of trivalent holmium, erbium, and thulium in aluminum garnet and the emission interpolating between them due to other active ions are superposed, so that the signal light in the wavelength range of 1.6 μm is obtained. A wide bandwidth amplification effect occurs. Nd ³⁺ , Tm ²⁺ , Yb ³⁺ and Lu ⁴⁺ ions function as activators for causing active ions to emit light.

In order to generate active ions having a valence of 2 or 4 and Tm ²⁺ ions or Lu ⁴⁺ ions, it is effective to use the compensation of the valence, and therefore, in the present invention. Produces an ion having a tetravalent valence by adding at least one element selected from Mg, Ca or Sr, and further Ti, Z
An ion having a divalent valence is generated by adding one or more elements selected from r, Hf, and Ge.

An energy diagram conceptually illustrating the present invention is shown in FIG. Needless to say, the energy levels are slightly different depending on the type and valence of the active ions even if they have the same orbit. That is, the central wavelength to be amplified changes due to a slight difference in level position, which causes an amplification effect in a wide wavelength range.

The advantage of the garnet crystal waveguide according to the present invention is that the above-mentioned light source for excitation is low in price, which will be further described below.

First, since the fluorescence of rare earth ions is used for the principle of stimulated emission, it can be mentioned that the wavelength stability is excellent. Since garnet crystal is used as the material, it is thermally and chemically stable and has a long life. It is a very small element, and except for the excitation light source, the total length is about 20 mm,
The thickness can be selected to be about 0.5 mm and the width can be selected to be about 1 to 5 mm within a range that is easy to handle.

Since it is a waveguide type component, it is naturally easy to couple it with another waveguide type device. The GGG crystal substrate used for fabrication is easily available, relatively inexpensive, and has advanced production / control technology. The crystal growth technology by liquid phase epitaxial growth method has been completed. Further, it is excellent in workability, is easy to perform waveguiding, and can be mass-produced to further reduce the price.

As described above, according to the present invention, the substitution type GGG is used as the clad material on the GGG substrate, and the core material is appropriately selected so that it can be excited by the inexpensive 0.81 μm semiconductor laser. It is possible to provide a garnet crystal waveguide that functions as an element that can withstand practical use, which has a function of amplifying light in the wavelength region, is small, inexpensive, and can be easily connected to other waveguide components. Is.

[0018]

EXAMPLES The present invention will be described below based on specific examples, but the present invention is not limited to the garnet crystal waveguides described in these examples, and the present invention is not limited to these examples. It is needless to say that the present invention also includes combinations of specific examples in which various substitutions described below are appropriately made. This is because, by looking at these examples, it can be easily inferred that the same effect can be obtained by the combination thereof. Further, if it is described further, it is involved in the main part of the present invention, that is, the control of the refractive index and the light emission. Even if a material in which various ions involved in energy transfer or parts other than ions involved in valence control are appropriately substituted is proposed, it can be easily inferred from the present invention, and it is obviously included in the present invention. is there.

[0019]

Example 1 To use GGG as a substrate crystal and replace a part of gallium with aluminum to control the refractive index as a lower clad and an upper clad material, and to control the lattice constant to be almost the same value as the substrate. Eu _2.94 La _0.06 Al _0.425 selected from among those appropriately substituted with rare earth elements
A substitutional garnet crystal having a composition of Ga _4.575 O ₁₂ is used, the substrate itself is used, and neodymium, ytterbium, lutetium, holmium, and rare earth elements are used for the core layer.
Erbium and thulium are added, magnesium is added to the position of gallium, and further, the gadolinium and the amount of lanthanum are appropriately controlled so that the lattice constant is almost the same as that of the substrate, and a garnet crystal waveguide using a garnet crystal film is manufactured, The characteristics were evaluated.

G having a diameter of about 2 inches and a thickness of about 0.4 mm
A GG single crystal substrate {(111) orientation} is prepared, and Eu _2.94 La _0.06 Al which becomes a lower clad layer at a temperature of about 950 ° C. is formed on the substrate by a liquid phase epitaxial growth method using lead oxide and boron oxide as a melting material. the _{0.42 5} Ga _4.575 O ₁₂ garnet film was grown to a thickness of approximately 10 [mu] m. The lattice constant of this crystal film is 12.382 Å, which is approximately 12.38 of that of the substrate.
It was about the same as 3Å. In order to control the refractive index, the amount of gallium substituted was about 15% of the aluminum site. The refractive index in the wavelength range of 1.5 μm was about 1.92. Refractive index of GGG which is a substrate material
The value was slightly smaller than 93. In addition, as a result of compositional analysis, unintended elements such as lead, boron, and platinum were detected although they were in very small amounts. This is a mixture of lead and boron, which are the main components of the flux, and platinum, which is a crucible material, during the growth process.

Then, a substitutional GGG crystal film containing neodymium, ytterbium, lutetium, holmium, erbium, thulium and magnesium, which is to be the core layer, is formed in the liquid phase using lead oxide and boron oxide as the flux as in the lower cladding. It was grown at a temperature of about 950 ° C. to a thickness of about 5 μm by an epitaxial growth method. It should be noted that gallium was not replaced with aluminum so that the refractive index was about the same as that of the substrate. Further, since the change in the refractive index due to the substitution of the rare earth element is small, the refractive index of the core layer is slightly affected by magnesium, but hardly affected,
It is about 0.01 larger than the cladding. Of the additional elements, holmium (H
o ³⁺ ), erbium (Er ³⁺ , Er ⁴⁺ ), thulium (T
m ³⁺ , Tm ⁴⁺ ), and ytterbium (Yb ⁴⁺ ), and their contents are approximately equal to each other, and the total content is about 10% of the total rare earth elements. The activators are, of course, neodymium (Nd ³⁺ ), ytterbium (Y
b ³⁺ ) and lutetium (Lu ⁴⁺ ) ions. The valence of these ions can be partially controlled to be tetravalent by adding magnesium.

To control the lattice constant, gadolinium was selected as the main portion of the rare earth element, and lanthanum and yttrium were used to correct the lattice distortion caused by other rare earth elements and magnesium. Although the substitution may cause the lattice constant to be slightly different from that of the substrate, it is not necessary to intentionally stick to the lattice matching as long as the crystal growth is not hindered. If there is a lattice mismatch to the extent that crystal growth is difficult, the lattice mismatch is relaxed by controlling the amount of lanthanum or scandium that does not contribute to absorption / emission in the infrared region to grow the core layer. It is quite possible to do.

Next, for the substrate on which the core layer has been grown,
A mask for processing a core ridge was formed on the film by a photo process, and ion beam etching was performed to form a linear core ridge having a width of about 5 μm and a height of about 5 μm.

On the substrate on which the core ridge has been formed,
Eu _2.94 L to be an upper clad layer having a thickness of about 15 μm at a temperature of about 950 ° C. by a liquid phase epitaxial growth method using lead oxide and boron oxide as a melting material similarly to the lower clad layer.
core cross-section to form a waveguide structure 5 [mu] m × 5 [mu] m by growing a _0.06 Al _0.425 Ga _4.575 O ₁₂ garnet film.

Finally, the waveguide was cut into a length of about 20 mm and the end face was polished to complete the production of the garnet crystal waveguide. This waveguide has a structure whose conceptual diagram is shown in FIG.

Table 1 shows a summary of this waveguide. In addition,
A 0.81 μm semiconductor LD was used for excitation.

[0027] Table 1 garnet crystal waveguide Summary Part 1 substrate material: GGG cladding _{material: Eu 2.94 La 0.06 Al 0.425 Ga} 4.575 O
₁₂ core materials: (Y, La, Nd, Yb, Lu, Ho, E
r, Tm, Mg): GGG Excitation light source: AlGaAs semiconductor laser (wavelength 0.80
6 μm) Gain in wavelength range of 1.6 μm: 25 dB or more Gain coefficient: 1 dB / mW or more Wavelength of gain 20 dB or more: 0.7 μm

The gain coefficient is an amplification factor per 1 mW of pumping light. As can be seen from this table, this waveguide had high performance.

[0029]

Example 2 As compared with Example 1, as a clad material,
Eu _2.84 La with slightly increased aluminum content
A garnet crystal film having a composition of _0.16 Al _0.6 Ga _4.4 O ₁₂ was grown at a temperature of about 980 ° C. by a liquid phase epitaxial growth method using lead oxide and boron oxide as a fluxing agent, and titanium was used as a core material instead of magnesium, and a rare earth element was used. As elements, besides gadolinium, lanthanum and yttrium, neodymium, ytterbium, dysprosium, holmium,
A waveguide was prepared by growing a garnet crystal film containing erbium and thulium at a temperature of about 980 ° C. by a liquid phase epitaxial growth method using lead oxide and boron oxide as a flux, and evaluated its characteristics. Naturally, the upper clad of these waveguides has a thickness of about 15 μm under the same conditions as the lower clad.
It has grown to. Table 2 shows the characteristics of these waveguides. A 0.81 μm semiconductor LD was used for excitation.

Table 2 Summary of Garnet Crystal Waveguide Part 2 Substrate Material: GGG Cladding Material: Eu _2.84 La _0.16 Al _0.6 Ga _4.4 O ₁₂ Core Material: (Y, La, Nd, Yb, Dy, Ho, E
r, Tm, Ti): GGG Excitation light source: AlGaAs semiconductor laser (wavelength 0.80
6 μm) Gain in wavelength range of 1.6 μm: 25 dB or more Gain coefficient: 1 dB / mW or more Wavelength of gain 20 dB or more: 0.7 μm

As can be seen from Table 2, the performance of these waveguides was satisfactory.

The refractive index of the clad was about 1.925 in the wavelength range of 1.5 μm. The lattice constant of the crystal film used for these clads or cores is 12.3.
It was 84 Å, which was almost the same as 12.383 Å of the substrate. Among the additional elements, dysprosium (Dy ²⁺ ), holmium (Ho ²⁺ , H) are directly involved in light emission.
o ³⁺ ), erbium (Er ²⁺ , Er ³⁺ ), thulium (T
m ³⁺ ), and their contents are equal to each other, and the total amount is about 10% of the whole rare earth elements. The activators are of course the neodymium (Nd ³⁺ ), ytterbium (Yb ³⁺ ) and thulium (Tm ²⁺ ) ions. The valence of these ions can be partially controlled to be divalent by adding titanium ions (Ti ⁴⁺ ).

[0033]

Example 3 A garnet crystal waveguide is prepared by using a crystal film in which calcium and strontium are added to the core layer in addition to neodymium, ytterbium, lutetium, holmium, erbium and thulium, except that the clad material is the same. Was produced. It is needless to say that the refractive index of the core layer is slightly larger than that of the clad as in the substrate, and the lattice constant is made equal to that of the substrate by controlling the amounts of gadolinium, yttrium and lanthanum. Calcium and strontium are divalent ions, and it was confirmed from the measurement of the fluorescence lifetime that the tetravalent ions of ytterbium, lutetium, erbium and thulium were increased to compensate the electric value. Table 3 shows the characteristics of these waveguides.
Shown in. It should be noted that calcium ions and strontium have large ionic radii and mainly substitute the sites of rare earth elements surrounded by oxygen dodecahedrons. As the replacement amount,
In total, the content of ytterbium, lutetium, erbium, and thulium was set to be approximately the same. It goes without saying that the activator and the active ion are the same as in Example 1. In addition, for excitation,
A semiconductor LD of 0.81 μm was used.

[0034] Table 3 garnet crystal waveguide Summary Part 3 substrate material: GGG cladding _{material: Eu 2.94 La 0.06 Al 0.425 Ga} 4.575 O
₁₂ core materials: (Y, La, Nd, Yb, Lu, Ho, E
r, Tm, Ca, Sr): GGG Excitation light source: AlGaAs semiconductor laser (wavelength 0.80
6 μm) Gain in wavelength range of 1.6 μm: 25 dB or more Gain coefficient: 1 dB / mW or more Wavelength of gain 20 dB or more: 0.7 μm

As can be seen from Table 3, these waveguides were of high performance.

A waveguide having a core layer containing neither neodymium nor lutetium as an activator was formed by the same method. However, we must not forget to control the refractive index and the lattice constant to the same level as the substrate. The characteristics were evaluated by directly exciting the active ions with a titanium sapphire laser in order to excite this waveguide with a laser having a wavelength in the vicinity of 1 μm, and it showed almost the same high performance as the characteristics shown in Table 3. . Similar performance was obtained when an InGaAs strained superlattice semiconductor laser was used instead of the titanium sapphire laser.

[0037]

[Embodiment 4] As in Embodiment 2, as a cladding material, Eu _2.84 L with a slightly increased content of aluminum was used.
A garnet crystal film having a composition of a _0.16 Al _0.6 Ga _4.4 O ₁₂ was grown at a temperature of about 980 ° C. by a liquid phase epitaxial growth method using lead oxide and boron oxide as a fluxing agent, and zirconium, hafnium and A garnet crystal film containing germanium, which contains neodymium, ytterbium, holmium, erbium, and thulium as a rare earth element in addition to gadolinium, yttrium, and lanthanum by a liquid phase epitaxial growth method using lead oxide and boron oxide as a flux at about 980 ° C. A waveguide grown at a temperature was prepared and its characteristics were evaluated. Naturally, the upper clad of these waveguides was grown to a thickness of about 15 μm under the same conditions as the lower clad. Table 4 shows the characteristics of these waveguides. For excitation, 0.81 μm
The semiconductor LD of was used.

Table 4 Summary of Garnet Crystal Waveguide Part 4 Substrate Material: GGG Cladding Material: Eu _2.84 La _0.16 Al _0.6 Ga _4.4 O ₁₂ Core Material: (Y, La, Nd, Yb, Ho, Er, T
m, Zr, Hf, Ge): GGG Excitation light source: AlGaAs semiconductor laser (wavelength 0.80
6 μm) Gain in wavelength range of 1.6 μm: 25 dB or more Gain coefficient: 1 dB / mW or more Wavelength of gain 20 dB or more: 0.7 μm

As can be seen from Table 4, the performance of these waveguides was satisfactory.

The lattice constant of the crystal film used for the core is
12.384Å, which was almost the same as 12.383Å of the substrate. Of the additional elements that are involved in direct light emission
Is holmium (Ho ²⁺ , Ho ³⁺ ), erbium (Er ²⁺ , Er ³⁺ ), thulium (Tm ³⁺ ), and their contents are equal to each other, and the total amount of the rare earth elements is at most 10. %. The activators are, of course, neodymium (Nd ³⁺ ) and ytterbium (Yb ³⁺ ) ions. The valence of these ions can be partially controlled to be divalent by adding zirconium ions (Zr ⁴⁺ ), hafnium ions (Hf ⁴⁺ ), and germanium ions (Ge ⁴⁺ ).

[0041]

[Embodiment 5] A garnet crystal is formed by using the same clad material as in Embodiment 1 except that neodymium, ytterbium, lutetium, holmium, erbium, thulium and magnesium, calcium and zirconium are added to the core layer. A waveguide was produced. It is needless to say that the refractive index of the core layer is slightly larger than that of the clad as in the substrate, and the lattice constant is made equal to that of the substrate by controlling the amounts of gadolinium, yttrium and lanthanum. Magnesium and calcium are divalent ions, and it was confirmed from the measurement of fluorescence lifetime that the tetravalent ions of ytterbium, lutetium, erbium and thulium were increased to compensate the electric value. It was also confirmed that zirconium was a tetravalent ion and some active ions were divalent. Table 5 shows the characteristics of these waveguides. The total substitution amount of magnesium ions, calcium ions and zirconium was set to be approximately the same as the total content of ytterbium, lutetium, holmium, erbium and thulium. It goes without saying that the activator and the active ion are the same as the respective ions described in Examples 1 and 2. A 0.81 μm semiconductor LD was used for excitation.

[0042] Table 5 garnet crystal waveguide Summary Part 5 substrate material: GGG cladding _{material: Eu 2.94 La 0.06 Al 0.425 Ga} 4.575 O
₁₂ core materials: (Y, La, Nd, Yb, Lu, Ho, E
r, Tm, Mg, Ca, Zr): GGG Excitation light source: AlGaAs semiconductor laser (wavelength 0.80
6 μm) Gain in wavelength range of 1.6 μm: 25 dB or more Gain coefficient: 1 dB / mW or more Wavelength of gain 20 dB or more: 0.7 μm

As can be seen from Table 5, these waveguides had high performance.

A waveguide having a core layer containing no activator neodymium or lutetium was formed by the same method. However, we must not forget to control the refractive index and the lattice constant to the same level as the substrate. The characteristics were evaluated by directly exciting the active ions with a titanium sapphire laser in order to excite this waveguide with a laser having a wavelength in the vicinity of 1 μm, and the performance was almost the same as the characteristics shown in Table 5. . Similar performance was obtained when an InGaAs strained superlattice semiconductor laser was used instead of the titanium sapphire laser.

[0045]

As described above, according to the present invention,
The substrate for forming the waveguide has Gd ₃ Ga ₅ O ₁₂ (GG
G) Using a single crystal substrate, the lower clad and the upper clad have substantially the same lattice constant as the substrate material, and gadolinium is replaced with at least another substitutable rare earth element or yttrium, and at least a part of gallium is converted into aluminum. Using the substituted garnet crystal film, the core layer for confining light, Nd, Dy, Ho, Er for rare earth elements,
Garnet crystal or substituted garnet crystal containing several kinds of elements combined from Tm, Yb and Lu, and added with one or more elements selected from Mg, Ca, Sr, Ti, Zr, Hf or Ge By using, 0.81 μm for excitation in the 1.6 μm wavelength region
It is possible to construct a waveguide having a high-performance amplifying action, which can use the semiconductor LD, and it is industrially advantageous.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a configuration of an optical waveguide according to the present invention.

FIG. 2 is an energy diagram conceptually showing the effect of the present invention.

[Explanation of symbols]

1 Garnet crystal substrate for forming a waveguide 2 Lower clad 3 Core layer 4 Upper clad 5 ⁴ F _3/2 level of trivalent neodymium ion 6 Divalent thulium ion, trivalent ytterbium ion or tetravalent ion Lutetium ion ² F _5/2 level 7 Divalent holmium ion, trivalent erbium ion or tetravalent thulium ion ⁴ I _11/2 level 8 Divalent holmium ion, trivalent erbium ion or 4 ⁴ I _13/2 level of valent thulium ion 9 _Ground level 10 Divalent dysprosium ion of trivalent holmium ion or ⁵ I ₆ level of tetravalent erbium ion 11 Divalent dysprosium ion of 3 valence ⁵ I ₇ level of holmium ion or tetravalent erbium ion 12 Divalent erbium ion, trivalent thulium ion or tetravalent ytterbium ion ³ H ₅ level 13 divalent erbium ions on, trivalent ³ H ₄ level of the thulium ions or tetravalent ytterbium ions

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hoaki Akira 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) Reference JP-A-6-3547 (JP, A) JP 3-149505 (JP, A) JP 5-281430 (JP, A) JP 5-301770 (JP, A) JP 5-226761 (JP, A) JP 1-257802 (JP , A) JP 5-134124 (JP, A) JP 4-147115 (JP, A) JP 6-224509 (JP, A) JP 64-81379 (JP, A) 6-507986 (JP, A) International Publication 92/021996 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/12 H01S 3/00-3/30

Claims (5)

(57) [Claims] 1. A lower cladding layer formed on a substrate,
The lower clad layer formed on the lower clad layer
The core layer having a large refractive index and processed into a ridge shape, and the core layer
Is formed on the cladding layer and the cladding layer, and refracted from the core layer.
Garnet crystal waveguide consisting of a low-index upper cladding layer
And the substrate is a Gd ₃ Ga ₅ O ₁₂ (GGG) single crystal substrate.
And the lower clad layer and the upper clad layer are made of Eu.
_2.94 La _0.06 Al _0.425 Ga _4.575 O
_And has a composition of ₁₂ and a lattice constant almost the same as that of the single crystal substrate.
A garnet crystal having Y, La, Nd, Yb, Lu, Ho, E
A substitutional GGG crystal film containing r, Tm, and Mg, wherein the core layer absorbs 0.81 μm of excitation light and ⁴ F
Excited to the _5/2 level, non-luminous transition to the ⁴ F _3/2 level
Nd ³⁺ ions and the energy absorbed by the Nd ³⁺
It is excited to the ² F _5/2 level by the transmission of _energy and emits light.
Yb that transfers energy to active ions that are directly involved
³⁺ ion and Lu ⁴⁺ ion and the active ion
Yes, it is excited by energy transfer to the ⁵ I ₆ level.
After that, it transits to the ⁵ I ₇ level without emitting light, and has a wavelength of 1.6 μm.
Ho ³⁺ ions and ions that stimulate and emit light by the signal light in the region
And ^{Er 4+} ion, undergoing energy transfer ³ H ₅ level
After being excited to the ³ position, it transitions to the ³ H ₄ level without light emission ,
1. Light is stimulated and emitted by signal light in the wavelength range of 1.64 μm
Tm ³⁺ ions and Yb ⁴⁺ ions, and energy
_-After being transmitted and excited to the ⁴ I _11/2 level,
The light transitions to the ⁴ I _13/2 level and emits light in the 1.6 μm wavelength range.
Er ³⁺ ions that stimulate and emit light by signal light, and
A garnet crystal waveguide comprising Tm ⁴⁺ ions . 2. A lower cladding layer formed on a substrate,
The lower clad layer formed on the lower clad layer
The core layer having a large refractive index and processed into a ridge shape, and the core layer
Is formed on the cladding layer and the cladding layer, and refracted from the core layer.
Garnet crystal waveguide consisting of a low-index upper cladding layer
And the substrate is a Gd ₃ Ga ₅ O ₁₂ (GGG) single crystal substrate.
And the lower clad layer and the upper clad layer are made of Eu.
_2.84 La _0.16 Al _0.6 Ga _4.4 O ₁₂ pair
And has substantially the same lattice constant as the single crystal substrate
Garnet crystal, wherein the core layer is Y, La, Nd, Yb, Dy, Ho, E
It is a substitutional GGG crystal film containing r, Tm, and Ti, wherein the core layer absorbs 0.81 μm of excitation light and ⁴ F
Excited to the _5/2 level, non-luminous transition to the ⁴ F _3/2 level
Nd ³⁺ ions and the energy absorbed by the Nd ³⁺
It is excited to the ² F _5/2 level by the transmission of _energy and emits light.
Yb that transfers energy to active ions that are directly involved
³⁺ ion and Lu ⁴⁺ ion and the active ion
Yes, it is excited by energy transfer to the ⁵ I ₆ level.
After that, it transits to the ⁵ I ₇ level without light emission and has a wavelength of 1.6 μm.
Dy ²⁺ ions and stimulated emission of light by signal light in the region
And ^{Ho 3+} ions, undergoing energy transfer ³ H ₅ level
After being excited to the ³ position, it transitions to the ³ H ₄ level without light emission ,
1. Light is stimulated and emitted by signal light in the wavelength range of 1.64 μm
Tm ³⁺ and Er ²⁺ ions, and energy
_-After being transmitted and excited to the ⁴ I _11/2 level,
The light transitions to the ⁴ I _13/2 level and emits light in the 1.6 μm wavelength range.
Er ³⁺ ions that stimulate and emit light by signal light, and
A garnet crystal waveguide comprising Ho ²⁺ ions . 3. A lower clad layer formed on a substrate,
The lower clad layer formed on the lower clad layer
The core layer having a large refractive index and processed into a ridge shape, and the core layer
Is formed on the cladding layer and the cladding layer, and refracted from the core layer.
Garnet crystal waveguide consisting of a low-index upper cladding layer
And the substrate is a Gd ₃ Ga ₅ O ₁₂ (GGG) single crystal substrate.
And the lower clad layer and the upper clad layer are made of Eu.
_2.94 La _0.06 Al _0.425 Ga _4.575 O
_And has a composition of ₁₂ and a lattice constant almost the same as that of the single crystal substrate.
A garnet crystal having Y, La, Nd, Yb, Lu, Ho, E
Substitution type GGG crystal film containing r, Tm, Ca, Sr
The core layer absorbs excitation light of 0.81 μm and absorbs ⁴ F.
Excited to the _5/2 level, non-luminous transition to the ⁴ F _3/2 level
Nd ³⁺ ions and the energy absorbed by the Nd ³⁺
It is excited to the ² F _5/2 level by the transmission of _energy and emits light.
Yb that transfers energy to active ions that are directly involved
³⁺ ion and Lu ⁴⁺ ion and the active ion
Yes, it is excited by energy transfer to the ⁵ I ₆ level.
After that, it transits to the ⁵ I ₇ level without emitting light, and has a wavelength of 1.6 μm.
Ho ³⁺ ions and ions that stimulate and emit light by the signal light in the region
And ^{Er 4+} ion, undergoing energy transfer ³ H ₅ level
After being excited to the ³ position, it transitions to the ³ H ₄ level without light emission ,
1. Light is stimulated and emitted by signal light in the wavelength range of 1.64 μm
Tm ³⁺ ions and Yb ⁴⁺ ions, and energy
_-After being transmitted and excited to the ⁴ I _11/2 level,
The light transitions to the ⁴ I _13/2 level and emits light in the 1.6 μm wavelength range.
Er ³⁺ ions that stimulate and emit light by signal light, and
A garnet crystal waveguide comprising Tm ⁴⁺ ions . 4. A lower clad layer formed on a substrate,
The lower clad layer formed on the lower clad layer
The core layer having a large refractive index and processed into a ridge shape, and the core layer
Is formed on the cladding layer and the cladding layer, and refracted from the core layer.
Garnet crystal waveguide consisting of a low-index upper cladding layer
And the substrate is a Gd ₃ Ga ₅ O ₁₂ (GGG) single crystal substrate.
And the lower clad layer and the upper clad layer are made of Eu.
_2.84 La _0.16 Al _0.6 Ga _4.4 O ₁₂ pair
And has substantially the same lattice constant as the single crystal substrate
Garnet crystal, wherein the core layer is Y, La, Nd, Yb, Ho, Er, T
A substitutional GGG crystal film containing m, Zr, Hf and Ge.
The core layer absorbs excitation light of 0.81 μm and absorbs ⁴ F.
Excited to the _5/2 level, non-luminous transition to the ⁴ F _3/2 level
Nd ³⁺ ions and the energy absorbed by the Nd ³⁺
It is excited to the ² F _5/2 level by the transmission of _energy and emits light.
Yb that transfers energy to active ions that are directly involved
³⁺ ion and Lu ⁴⁺ ion and the active ion
Yes, it is excited by energy transfer to the ⁵ I ₆ level.
After that, it transits to the ⁵ I ₇ level without light emission and has a wavelength of 1.6 μm.
Ho ³⁺ ion that stimulates and emits light by the signal light in the region ,
After receiving energy transfer and being excited to the ³ H ₅ level,
It shifts to the ³ H ₄ level without light emission, and emits light in the 1.64 μm wavelength range.
Tm ³⁺ ions and E that stimulated emission of light by
r ²⁺ ion, and ⁴ I after energy transfer
After being excited to the _11/2 level, it emits ⁴ I _13/2 without emitting light.
Transition to level, light by the signal light of 1.6μm wave length range
Er ³⁺ ions and Ho ²⁺ ions that are stimulated to be emitted
A garnet crystal waveguide characterized by comprising. 5. A lower clad layer formed on the substrate,
The lower clad layer formed on the lower clad layer
The core layer having a large refractive index and processed into a ridge shape, and the core layer
Is formed on the cladding layer and the cladding layer, and refracted from the core layer.
Garnet crystal waveguide consisting of a low-index upper cladding layer
And the substrate is a Gd ₃ Ga ₅ O ₁₂ (GGG) single crystal substrate.
And the lower clad layer and the upper clad layer are made of Eu.
_2.94 La _0.06 Al _0.425 Ga _4.575 O
_And has a composition of ₁₂ and a lattice constant almost the same as that of the single crystal substrate.
A garnet crystal having Y, La, Nd, Yb, Lu, Ho, E
Substitution type GGG binding containing r, Tm, Mg, Ca, Zr
The core layer absorbs 0.81 μm of excitation light and absorbs ⁴ F.
Excited to the _5/2 level, non-luminous transition to the ⁴ F _3/2 level
Nd ³⁺ ions and the energy absorbed by the Nd ³⁺
It is excited to the ² F _5/2 level by the transmission of _energy and emits light.
Yb that transfers energy to active ions that are directly involved
³⁺ ion and Lu ⁴⁺ ion and the active ion
Yes, it is excited by energy transfer to the ⁵ I ₆ level.
After that, it transits to the ⁵ I ₇ level without emitting light, and has a wavelength of 1.6 μm.
Ho ³⁺ ions and ions that stimulate and emit light by the signal light in the region
And ^{Er 4+} ion, undergoing energy transfer ³ H ₅ level
After being excited to the ³ position, it transitions to the ³ H ₄ level without light emission ,
1. Light is stimulated and emitted by signal light in the wavelength range of 1.64 μm
Er ²⁺ ion, ^{Tm 3+} ion and ^{Yb 4+} Io
And the energy transfer to the ⁴ I _11/2 level
After being excited, it transits to the ⁴ I _13/2 level without emitting light ,
H that stimulates and emits light by signal light in the wavelength range of 1.6 μm
o ²⁺ ions, Er ³⁺ ions and Tm ⁴⁺ ions
A garnet crystal waveguide comprising: