JP3301043B2 - Garnet waveguide and method of using garnet waveguide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a garnet waveguide and a garnet waveguide.
The present invention relates to a method for using a garnet waveguide .

[0002]

2. Description of the Related Art Infrared light having wavelengths of 1.31 μm and 1.55 μm is used as signal light for optical communication. For example, when a communication network is formed, the fiber cable branches from the trunk line to the station and from the station to each subscriber. Therefore, the intensity of the signal light is reduced by the number of times of branching. At this time, if the intensity of the signal light is lower than the detection sensitivity of the light receiving element, the signal cannot be received. Therefore, it is necessary to amplify the signal after branching a certain number of times.

Conventionally, a method used to amplify such a signal is to convert an optical signal into an electric signal by a light receiving element, electrically process the signal, and then convert the signal to an optical signal again. That is the mainstream. However, according to this method, a signal is transmitted at a high speed, but a time delay is caused by the amount of signal processing, which is not suitable for ultra-high-speed communication in which optical communication is oriented.

[0004] For this reason, recently, attempts have been made to directly amplify an optical signal as light.

In these techniques, rare earth elements (such as praseodymium, neodymium, and erbium) or chromium that exhibit fluorescence in the infrared region are dispersed in glass or optical crystal (host material), and signal light and excitation light are simultaneously incident. When electrons of active ions absorb the excitation light and emit light having the same wavelength as the signal light, the principle is that an amplification action is generated using the signal light as a seed.

[0006] Problems with direct optical amplification that have been attempted in the past include the following. First, when glass is used, a fiber is usually used, but it is difficult to increase the amount of active ions added, so that the efficiency of fluorescence per unit length is reduced and the amplification gain is increased. Requires a fiber amplifier of sufficient length. For this reason,
As the performance of the amplifier becomes higher, the size of the amplifier becomes larger, and at the same time, the price becomes higher because a fiber type component is used.

Further, the fiber amplifier has a disadvantage that an expensive laser diode must be used as an excitation light source for generating fluorescence.

[0008] Large-sized, high-priced, high-performance amplifiers are being developed on the premise that they are used in relay stations and the like. Are of different species.

For this reason, optical amplifiers used near homes are miniaturized by using optical crystals that can increase the efficiency of fluorescence, and directional couplers used for simultaneously inputting signal light and pump light are used for optical amplifiers and the like. Using a planar optical circuit component formed by lithography technology, an inexpensive 0.81μ
It is conceivable to reduce the cost by using a GaAlAs LD of m.

Heretofore, by constructing a resonator by using the end face of the crystal as a mirror, and utilizing fluorescence as in the case of amplification, a solid-state laser has been operated or has been shown to have the possibility. Yttrium aluminum garnet (YAG) to which trivalent ions of holmium, erbium, thulium and chromium are added, gadolinium gallium garnet (GGG), lithium niobate, yttrium aluminate and the like. They are,
Since the electrons of active ions arranged in the crystal emit light with high efficiency by the action of the crystal field, light is amplified in a sufficiently short length as compared with the fiber amplifier.

However, the wavelength used for communication is 1.3 μm.
In the m band, 1.31 ± 0.02 μm and its center is 1.31 μm
On the other hand, for example, when a neodymium-substituted optical crystal is used, the center wavelength is 1.32 to 1.33 μm, and the gain bandwidth product is not large. In some cases, a limited gain may not be obtained. Similarly for other trivalent active ions, the fluorescence has a sharp peak with respect to the wavelength due to the action peculiar to the crystal field, and the bandwidth is narrowed. That is, a material obtained by adding a trivalent active ion to an optical crystal that has been conventionally studied may not be able to obtain the required minimum performance.

[0012]

By the way, as a material which can solve the problems of the optical amplifier materials which have been conventionally studied, there is a garnet crystal having chromium tetravalent ions as active ions. . This is because tetravalent chromium ions generate fluorescence in a broad band from 1.3 μm to 1.6 μm. However, it is known that chromium becomes trivalent simply by replacing the octahedral coordination of gallium, aluminum or iron of garnet. Therefore, usually, it is conceivable to introduce divalent ions such as calcium to make chromium tetravalent to compensate for the charge.

[0013] Even if chromium ions can be made tetravalent by charge compensation, the following problem remains. It is attributable to a light source that excites tetravalent chromium ions and to an absorption edge of chromium ions.

The tetravalent chromium ion has an absorption peak near a wavelength of 1 μm, and a light source of that wavelength is required for highly efficient excitation. Currently, lasers oscillating in the wavelength region include LD, Y of 0.98 μm and 1.1 μm.
There are AG laser and titanium sapphire laser. These LDs are small but expensive. YAG lasers and titanium sapphire lasers are expensive and large. That is, it is disadvantageous to construct a small and low-priced amplifier. Further, although tetravalent chromium ions exhibit broadband fluorescence, there is a disadvantage that the absorption edge extends to a wavelength slightly higher than 1.3 μm, and the amplification factor in the 1.3 μm band decreases.

According to the present invention, to solve such a problem, tetravalent chromium ions are efficiently excited and 1.3 μm
It is an object of the present invention to provide a garnet waveguide using a garnet crystal that does not reduce the amplification factor of the m band and a method of using the garnet waveguide .

[0016]

According to the present invention, there is provided a garnet waveguide, comprising:
A garnet waveguide serving as a core, wherein the garnet is
The crystal film has a general formula R ₃ B ₅ O ₁₂ (where R represents any one of yttrium or bismuth and a rare earth element other than neodymium having a valence of 3, and B represents aluminum, gallium, scandium and represents any kind of iron.) a garnet crystal represented by, while replacing a part of the general formula B in chromium, in the above general formula
In order to control the valence of substituted chromium by substituting a part of R with neodymium, a part of R in the above general formula is at least one element selected from beryllium, calcium, magnesium and strontium. It is characterized by being replaced . Further, in the above configuration, the substitution amount of chromium, neodymium, beryllium, calcium, magnesium, and strontium may be 2 mol% or less. on the other hand,
The method of using the garnet waveguide according to the present invention is as follows. A 0.81 μm pump light and a 1.3 μm signal light are input to the garnet waveguide according to claim 1 or 2.
It is characterized in that the signal light in the region is amplified.

That is, the present invention not only satisfies the electric neutral condition by introducing divalent ions selected from beryllium, calcium, magnesium and strontium to generate tetravalent chromium ions, Further, by substituting a part of the rare earth element with neodymium, the low-priced 0.8 is utilized by utilizing the fluorescence of trivalent neodymium ions.
First, neodymium ions are excited by an aluminum / gallium / arsenic LD having a wavelength of 1 μm to generate 1.06 μm fluorescence with high efficiency.

The emission of 1.06 μm can excite tetravalent chromium ions with high efficiency.
Amplification is possible in a wide wavelength range up to.

On the other hand, 1.3 .mu.
In the region of m, neodymium ions also show fluorescence (1.
(Intensity of about 30% or less with respect to 06 μm), it is possible to prevent a decrease in amplification factor.

In the present invention, the replacement amount of chromium, neodymium and alkaline earth metal is preferably about 2 mol% or less from the viewpoint of efficiency and self-quenching.

[0021]

EXAMPLES The present invention will be described below with reference to specific examples, but it is needless to say that the present invention is not limited to these examples.

(Example 1) An yttrium aluminum garnet substrate having a diameter of 2 inches (about 50 mm) and a thickness of 0.4 mm (mirror-finished in the [111] direction of a YAG substrate) was prepared, and one of tetrahedral coordination of aluminum was prepared. Part (2 mol%) is replaced by chromium ion, 2 mol% of yttrium is replaced by neodymium, 2 mol% of yttrium is replaced by calcium in order to control chromium ion to be tetravalent, and the lattice constant is made substantially equal to that of the substrate. For this purpose, part of yttrium is replaced by bismuth or a rare earth element (lanthanum, cerium, praseodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium) to obtain a waveguide structure. Replaces part of gallium with gallium The liquid phase epitaxial growth method with flux boron oxide and lead oxide control was substituted YAG crystal film was formed to a thickness of about 4μm at a growth temperature of about 1000 ° C..

These crystal films have a slightly higher refractive index (about 1%) with respect to the substrate as they are, and have a waveguide structure. However, in order to further improve light confinement, an ion beam is used. A ridge having a width of about 4 μm (having a height equal to the thickness of the crystal film) is formed by etching, and a YAG crystal same as the substrate crystal is formed thereon by liquid phase epitaxial growth to a thickness of about 10 μm. Thus, a buried waveguide was produced.

These buried waveguides were cut to a length of about 10 mm, and the end faces were optically polished and the characteristics thereof were examined. As a result, due to the effect of trivalent neodymium ions and tetravalent chromium ions, 0.81 μm was obtained. In the wavelength region of 1.3 to 1.6 μm with the excitation light, as shown in FIG. 1, good amplification characteristics were exhibited, and the gain was about 15 dB or more. It was confirmed that the characteristics did not deteriorate due to the emission of neodymium ions even in the vicinity of 1.3 μm (the peaks in the 1.3 μm region in FIG. 1 are due to the neodymium ion amplification action). The waveguide loss is 0.2 dB / cm.
It was below.

(Example 2) By operating in the same manner as in Example 1, chromium,
The substitution amount of the neodymium alkaline earth metal is set to 0.5 mol%, and the substitutional garnet crystal film in which beryllium, magnesium, and strontium are selected as divalent ions for controlling the valence of chromium ions is formed of lead oxide and boron oxide. About 1000 ° C. by a liquid phase epitaxial growth method using
At a growth temperature of about 4 μm. As in Example 1, the lattice constant was controlled by substituting a rare earth element, and the refractive index was controlled by substituting aluminum with gallium or scandium.

Although these crystal films had a slightly higher refractive index (about 2%) with respect to the substrate as they were in the same manner as in Example 1, they had a waveguide structure, but further improved light confinement. For this purpose, a ridge having a width of about 4 μm (having a height equal to the thickness of the crystal film) is formed by ion beam etching in the same manner as in Example 1, and the same YAG crystal as the substrate crystal is formed thereon. Was formed to a thickness of about 13 μm by a liquid phase epitaxial growth method to produce a buried waveguide.

These buried waveguides were cut to a length of about 10 mm, and the end faces were optically polished and the characteristics were examined. As a result, pumping light of 0.81 μm in a wavelength region of 1.3 to 1.6 μm was obtained. Shows an amplification characteristic of about 1.3 dB / mW or more,
The gain was about 25 dB or more. The waveguide loss is 0.1
It was less than dB / cm.

[0028]

As described above, according to the present invention,
By utilizing the 1.06 μm and 1.3 fluorescence of trivalent neodymium ion, tetravalent chromium ion can be activated and 1.3 μm using low-cost 0.81 μm LD.
Compensate for the excitation light absorption of tetravalent chromium ions at 1.3 m
A waveguide device capable of amplifying a wide band of up to 1.6 μm can be provided, which has great industrial advantages.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of an optical amplification characteristic of a garnet waveguide according to the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-358130 (JP, A) Brian M. et al. , Color of chromium-doped yttrium a luminium garnet single-crystal fiber using a divergent codope, J. et al. Appl. Phys. , Vol. 70, No. 7, pp. 3775-3777. (58) Field surveyed (Int. Cl. ⁷ , DB name) H01S 3/00-3/30

Claims (3)

(57) [Claims] A garnet crystal film is used as a core of a waveguide.
A garnet waveguide that, the garnet crystal film, the general formula R ₃ B ₅ O ₁₂ (wherein, R represents yttrium or bismuth, and trivalent either one rare earth element other than neodymium having a valence And B represents any one of aluminum, gallium, scandium and iron.)
A garnet crystal represented by the formula: wherein a part of B in the above general formula is substituted with chromium, and a part of R in the above general formula is substituted with neodymium, and the valence of the substituted chromium is controlled. In the above general formula, a part of R is not replaced by one or more elements selected from beryllium, calcium, magnesium, and strontium.
Garnet waveguide, characterized in that that. 2. The garnet waveguide according to claim 1, wherein the substitution amount of chromium, neodymium, beryllium, calcium, magnesium, and strontium is 2 mol% or less. 3. A garnet waveguide according to claim 1 or 2, wherein 0.81 μm of pump light and 1.3 μm signal light are input to amplify the 1.3 μm signal light. Characteristic usage of garnet waveguide.