JP2000252569A - Light control element and light control composite element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To negative-control the intensity of incident light over a wavelength range for optical fiber communication stably, according to the intensity of the incident light itself, by controlling the respondable wavelength range of a light transmitting medium by a voltage applied to an optical path. SOLUTION: Three pairs of control electrodes 2A and 2B, 2C and 2D, and 2E and 2F being opposed to each other are formed on a pair of principal surfaces of a bulk substance 1 which forms an optical path. Each pair of opposed control electrodes is arranged on a light control element 5C, 5D, 5E along the direction of transmission of light inside the bulk substance 1. Each respondable wavelength range of the elements 5C-5E is shifted as shown by 20A-20C. If incident light having a wavelength of 1.532 μm for example enters the light control composite elements, light is transmitted without occurrence of a negative absorption phenomenon in the elements 5C, 5D, but the negative absorption phenomenon occurs in the element 5E. Accordingly, it is possible to form a light controlling element capable of negative-controlling the intensity of incident light in a wavelength range for optical fiber communication stably, according to the intensity of the incident light itself.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an element for negatively controlling the intensity of incident light in an optical fiber communication wavelength band (wavelength 1.5 .mu.m band) according to the intensity of the incident light itself. The present light control element can be used, for example, for optical information processing using a system using an optical fiber that can realize very low-loss optical signal transmission.

[0002]

2. Description of the Related Art In the field of optoelectronics such as optical information processing and optical communication, an optical-optical switch, that is, an element for controlling light by light (optical control element), which can respond faster than an electric circuit is required. It has been. Many light control elements that use the nonlinear optical effect have been proposed as light control elements for controlling the intensity of signal light. Specifically, there is an apparatus utilizing the fact that the refractive index of a nonlinear optical medium changes depending on the intensity of signal light. To realize such an element,
A medium having a very large nonlinear optical constant is required.
However, in the case of existing materials, the value of the nonlinear optical constant is one to two orders of magnitude smaller than the applicable level as a light control element.

On the other hand, Japanese Patent Application Laid-Open Nos.
In the technique disclosed in Japanese Patent Application Laid-Open No. 9-26605, the intensity of the signal light is controlled by control light having the same wavelength as the signal light. That is, a signal light having a predetermined wavelength is incident on a solid light transmitting medium doped with, for example, erbium. Erbium is characterized in that the degree of excitation absorption from a metastable level to its excitation level for signal light of a predetermined wavelength is greater than the degree of base absorption from a ground level to an excitation level. As a result, when the intensity of the signal light propagating in the light transmitting medium increases, the light transmittance decreases in accordance with the increase in the intensity. This phenomenon is a negative absorption phenomenon of a mechanism different from the nonlinear optical effect. Using this effect, if the control light of the same wavelength as the signal light is also incident on the optical path of the signal light while the signal light is incident on the light transmitting medium, the light transmittance of the signal light decreases. Then, the intensity of the transmitted light is reduced and the light is turned off. This phenomenon occurs, for example, in a solid light transmitting medium doped with erbium, at a wavelength of 770 nm-830.
It is said to be expressed in the range of nm.

[0004]

In order to expand the field of application of the optical control element, it is necessary to expand the wavelength range that can be used as signal light. It is significant to realize a light control element that uses band light as signal light. Further, a two-terminal light control element is required for an optical signal inverter (optical inverter) which is indispensable as a component of an all-optical optical logic circuit. Therefore, a light control element having a function of a two-terminal element for controlling the intensity of signal light based on the intensity information of the signal light is also demanded.

However, in the conventional light control device using the nonlinear optical effect, in many materials, the wavelength region in which the nonlinear optical characteristics are efficiently exhibited tends to interact with a short wavelength, that is, the electronic system of the material. Limited to areas with high energy. A large nonlinear optical effect cannot be expected on the long wavelength side, for example, 1.5 μm band light which is frequently used in optical fiber communication.

On the other hand, Japanese Patent Application Laid-Open Nos.
In an optical control element utilizing negative absorption as disclosed in Japanese Patent Application Laid-Open No. 9-26605, as described above, the signal light wavelength is limited to 770-830 nm, and
No stable expression of negative control has been confirmed for signal light in the μm band.

An object of the present invention is to provide an optical control element capable of stably controlling the intensity of incident light in the wavelength range for optical fiber communication (wavelength 1.5 μm band) according to the intensity of the incident light itself. That is.

[0008]

The present invention has a wavelength of 1.5 μm.
An optical path for injecting m-band incident light and emitting outgoing light, the optical path including at least an erbium-containing light-transmitting medium is provided. In a light control element that performs negative control in a specific response wavelength region according to the intensity of light, the light control element includes a voltage applying unit that applies a voltage to an optical path, and the voltage applied to the optical path causes the light transmitting medium to emit light. The present invention relates to a light control element for controlling a response wavelength region.

Further, the present invention relates to a light control composite device comprising a plurality of light control devices for a wavelength band of 1.5 μm,
A plurality of light control elements are connected in series, and each light control element is an optical path for injecting incident light in a wavelength of 1.5 μm and emitting outgoing light, the light path containing at least erbium. An optical path made of a transmissive medium is provided, the intensity of outgoing light is negatively controlled in a specific response wavelength region according to the intensity of incident light in the light transmissive medium, and each light in each light control element is controlled. It is characterized in that the transmissive media have different response wavelength ranges.

[0010] The present inventor has sought to solve the above problems.
A light-transmitting medium containing Er ³⁺ ions and a wavelength of 1.5 μm;
The interaction with m-band incident light was studied in detail. As a result, due to the energy constraint of Er ³⁺ ions, 1.5 μm
Negative absorption phenomenon (a phenomenon in which the intensity of outgoing light changes to negative in response to a change in the intensity of incident light in response to only m-band incident light.
(See JP-A-4-308821 and JP-A-9-26605) The energy level that can substantially contribute to the expression of the light is very limited. As a result, of the incident light in the 1.5 μm band, It was found that the negative absorption phenomenon occurred only in an extremely narrow wavelength range. Also, as a result of the extremely narrow wavelength range of the incident light that causes such a negative absorption phenomenon, a stable negative absorption phenomenon has not been confirmed for incident light in the 1.5 μm band. Thought.

The above technical contribution of the present inventor will be further described. The inventor measured the light transmission spectrum of a light-transmitting medium (length: 14 mm) for a light control element made of a single crystal of lithium niobate to which 3% of erbium was added at room temperature near a wavelength of 1.55 μm. It was shown to. FIG.
As is clear from FIG. 7, a sharp absorption peak appeared around a wavelength of 1.530 μm.

FIG.³⁺Energy level diagram of
You. Er³⁺Is the ground level^FourI_15/2Excited level from^TwoH_9/2
Have several excitation levels (see FIG. 2 for some of them).
Level only). With 1.530μm wavelength shown in Fig. 1
The near absorption is shown in FIG. ³⁺Energy level of ion
E0 (^FourI_15/2) -E1 (^FourI_13/2) Between levels
Transition σ₁, And E1 (^FourI_13/2) -E2 (^FourI_9/2)
Transition between levels σ_TwoIt is due to. That is, the wavelength 1.
With only a single incident light in the 5 μm band, the above two transitions
Only triggered, transitions between higher levels^Four
I_9/2−^FourS_3/2,^FourS_3/2−^TwoH_9/2(Shown in FIG. 2
Is not induced, the absorption of incident light occurs.
The range of these wavelengths becomes very narrow.

The present inventor has found that energy transitions occur easily.
If no level exists, the negative absorption phenomenon does not occur.
In the light-transmitting medium, the negative
Is limited to wavelengths around 1.530 μm.
Expected to be. Furthermore, the negative absorption phenomenon is E1 (^Four
I_13/2) -E2 (^FourI_9/2) Transition between levels σ_TwoBy
Because it is a phenomenon that is caused, wavelength selectivity is further improved
I thought it would strengthen. Because the normal absorption process
And E0 (^FourI_15/2) -E1 (^FourI_13/2) Transition between levels
σ₁, And E1 (^FourI_13/2) -E2 (^FourI_9/2) Level
Transition between σ_TwoThrough E2 (^FourI_9/2) Knocking on the level
The emitted electrons are relaxed A₄₃, B₃₂As a result, E1 (^FourI
_13/2) The level falls, and the number of electrons in the E1 level increases. This result
As a result, E1 ( ^FourI_13/2) -E2 (^FourI_9/2) Transition between levels
σ_TwoIs enhanced and electrons at the E1 level are pumped up.
As a result, the amount of incident light absorbed increases, resulting in a negative absorption phenomenon.
appear.

A wavelength 1.5 modulated at a frequency of 1 kHz.
Each incident light of 28 μm to 1.533 μm is made incident on the above-mentioned light-transmitting medium, and the change in the modulation state of the intensity of the emitted light is measured. The bottom part of FIG. 3 shows a modulation state of the incident light, that is, a temporal change of the intensity. Wavelengths 1.528, 1.529, 1.53 in order from the top in FIG.
For each wavelength of 0, 1.531, 1.532, and 1.533 μm, the time change of the intensity of the emitted light is shown.

For the incident light having the wavelengths of 1.528 μm and 1.533 μm, the modulation state of the output light intensity is exactly in phase with the modulation state of the incident light intensity, and the negative absorption phenomenon does not occur. . Wavelengths 1.529, 1.531, 1.
At each wavelength of 532 μm, a certain degree of negative absorption occurs, but it does not reach the phase opposite to the intensity modulation of the incident light. With respect to the incident light having the wavelength of 1.530 μm, the modulation state of the emission light intensity was almost completely opposite in phase to the modulation state of the incident light intensity. That is, it was found that the complete negative absorption phenomenon occurred only at an extremely limited wavelength of 1.530 μm.

In view of the above findings, the inventor of the present invention applies the light to the optical path when negatively controlling the intensity of outgoing light in a specific response wavelength region according to the intensity of incident light in a light transmissive medium. It has been conceived that the response wavelength region of the light-transmitting medium is controlled by the voltage. That is, according to the magnitude of the voltage applied to the optical path, the energy level intervals corresponding to the transitions σ ₁ and σ ₂ of Er ³⁺ are finely adjusted, and the wavelength at which the negative absorption phenomenon occurs is shifted. It has become possible to negatively control incident light of a desired specific wavelength.

In the present invention, the term "negative control" refers to controlling the intensity of emitted light through the negative absorption phenomenon described above. In addition, the incident light refers to light that enters the optical path of the light control element. Therefore, when the signal light is independently incident on the optical path, the intensity of the emitted light is negatively controlled by modulating the intensity of the signal light, so that a two-terminal light control element can be obtained. Alternatively, in addition to the signal light, the control light can be simultaneously incident on the optical path as the incident light. In this case, a three-terminal light control element can be realized. When using this element, for example, when the intensity of the signal light is constant, the intensity of the emitted light is constant when the control light is not simultaneously incident, whereas when the control light is simultaneously incident, the intensity of the emitted light is constant. Strength is reduced.

There are no particular restrictions on the method of applying the voltage.
For example, in the light control element 5A shown in FIG.
The plate-shaped bulk body 1 made of a light-transmitting medium forms an optical path. A pair of opposing control electrodes 2A and 2B are formed on a pair of main surfaces 1c and 1d of the bulk body 1. When incident light is incident from the incident surface 1a of the bulk body 1 as shown by the arrow 3, the light propagates inside the bulk body and is emitted from the emission surface 1b as shown by the arrow 4. Light control element 5B of FIG.
1, an optical waveguide 11 is provided on one main surface 10 a side of an optical waveguide substrate 10, and a pair of control electrodes 12 A and 12 B are provided on both sides of the optical waveguide 11.
The incident light enters the optical waveguide 11 as indicated by an arrow 3, propagates through the optical waveguide 11, and exits as indicated by an arrow 4. FIG.
In (b), at least Er ³⁺ is contained in the optical waveguide 11.
Must be contained.

Further, a plurality of light control elements are connected in series,
At this time, by making the response wavelength regions of the respective light-transmitting media in the respective light control elements different from each other, the response wavelength region in which the negative control can be performed can be expanded as the entire light control composite element. In order to make the response wavelength regions of each light control element different from each other, it is effective to make the voltage applied to the optical path different in each light control element as described above. FIG. 4C is a perspective view showing the light control composite device 15 according to the embodiment of the present invention.

In FIG. 4C, a flat bulk member 1 made of a light-transmitting medium forms an optical path. Three pairs of opposing control electrodes 2A and 2B, 2C and 2D, 2E and 2F are formed on a pair of main surfaces 1c and 1d of the bulk body 1. The opposing control electrodes of each pair are arranged along the light propagation direction in the bulk body 1. As a result, along the light propagation direction in the bulk body 1, the light control elements 5C, 5D,
5E is arranged. By making the applied voltages of the respective light control elements different from each other, the response wavelength region of each element is changed.

For example, assuming that lithium niobate containing erbium having a thickness of 1 mm is used as the light transmitting medium, as shown in FIG. 5, in the state where no voltage is applied to the optical path, as described above. A negative absorption phenomenon occurs near 1.530 μm (response wavelength region 20A in FIG. 5).
Here, by applying a voltage of, for example, 100 to 500 volts to the control electrode of the light transmitting medium that is the optical path,
As shown in FIG. 5 at 20B and 20C in the response wavelength region,
It can be shifted to around 1.531-1.532 μm.

In FIG. 4C, the elements 5C, 5D, 5
The response wavelength regions of E are respectively 20A, 20B, 2
Shift as shown at 0C. Then, when incident light having a wavelength of, for example, 1.532 μm is made incident on the light control composite element, this light propagates without generating a negative absorption phenomenon in the elements 5C and 5D and becomes negative in the element 5E. Sexual absorption phenomenon occurs. Therefore, the present light control composite device has:
Negative control can be performed on incident light having a wavelength in the range of 530 to 1.532 μm.

The base material of the light transmitting medium is, for example, glass,
It may be a dielectric, an organic compound, an organic polymer compound, or a liquid substance. However, when a voltage is applied to the optical path, the base material is preferably a dielectric material, and more preferably a ferroelectric material, so that the voltage can be applied efficiently. As the dielectric, rare earth garnets (particularly, yttrium aluminum garnet, lutetium aluminum garnet) are preferable. As the ferroelectric, lithium niobate, lithium tantalate, and a solid solution of lithium niobate-lithium tantalate are preferable. In particular, when the base material is a ferroelectric, the crystal lattice length changes due to the piezo effect, and the interval between the energy levels of Er ³⁺ easily changes.

When the base material of the light transmitting medium changes,
Since the interaction between the electronic state of the doped Er ^{3+ and} the electronic state of atoms (ions) of the surrounding base material changes,
The intervals between the energy levels in FIG. 2 and the corresponding absorption wavelengths change. Therefore, the response wavelength region of each light control element can be shifted by changing the base material of each light control element constituting the light control composite element. That is, in one embodiment of the light control composite device of the present invention, each light transmitting medium forming each light path of each light control device is made of erbium and a base material different from each other.

In many cases, when the content of erbium increases, the response wavelength region tends to shift to the longer wavelength side. Therefore, the base material has a structure capable of taking in a large amount of erbium, such as rare earth garnets. If a material is used, the wavelength adjustment range is widened.

Even when the base material is different for each light control element, by joining the respective light transmitting media to each other,
An integrated bulk body as shown in FIG. 4A can be manufactured, or an integrated optical waveguide substrate as shown in FIG. 4B can be manufactured. However, each light control element may be separate.

In each light control element, both the applied voltage and the base material of the light-transmitting medium can be changed, thereby increasing the difference in the response wavelength region between each light control element and the light control element. The response wavelength region of the entire control composite element can be further expanded.

The means for introducing the incident light to the light control element may be an optical fiber through which the incident light is propagated, or may be a spatial coupling method via a lens.

The light control device and light control composite device of the present invention can realize, for example, very low-loss optical signal transmission.
It can be used for optical information processing using a system using an optical fiber. Further, the optical switching element can be used in an application field such as an optical logic circuit element.

[0030]

As described above, according to the present invention, the intensity of incident light in the wavelength range for optical fiber communication (wavelength 1.5 μm band) can be stably made negative according to the intensity of the incident light itself. A controllable light control element can be provided.

[Brief description of the drawings]

FIG. 1 is a graph showing a light transmission spectrum near a wavelength of 1.55 μm for a light transmission medium for a light control element made of lithium niobate single crystal to which 3% of erbium is added.

FIG. 2 is an energy level diagram of Er ³⁺ .

FIG. 3 shows a wavelength 1.52 intensity-modulated at a frequency of 1 kHz.
It is a graph which shows the change of the modulation | alteration state of the intensity | strength of the emitted light when each incident light of 8 micrometers-1.533 micrometers is made to inject into the said light permeation medium.

4A is a perspective view schematically showing a light control element 5A, FIG. 4B is a perspective view schematically showing a light control element 5B, and FIG. 4C is a light control composite. FIG. 2 is a perspective view schematically showing an element 15.

FIG. 5 is a graph showing a relationship between a voltage applied to the light control composite device and a response wavelength region.

[Explanation of symbols]

1. Bulk body forming optical path, 2A, 2B, 2C, 2
D, 2E, 2F control electrode, 3 incident light, 4 outgoing light,
5A, 5B Light control elements, 5C, 5D, 5E Plural light control elements constituting light control composite element 15, 10 Optical waveguide substrate, 11 Optical waveguide forming optical path, 12A, 12
B control electrode of optical waveguide 11, 15 optical control composite element,
E0 ⁴ I _15/2 level position, E1 ⁴ I _13/2 level position, E2 ⁴
I _9/2 level, σ ₁ E0-E1 level transition, σ ₂ E1
-E2 between levels between transitions, A _43, B ₃₂ E2 relief from ⁽⁴ I _9/2) E1 to ⁽⁴ I _13/2)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H079 AA02 AA12 BA04 CA07 DA03 EA03 EA11 EB04 EB05 GA01 HA04 HA07 KA11 5F072 AB01 AB20 AK03 AK07 JJ13 JJ20 MM20 RR01 YY15

Claims (9)

[Claims] 1. An incident light having a wavelength of 1.5 μm is made incident,
An optical path for emitting outgoing light, comprising an optical path made of a light-transmitting medium containing at least erbium, wherein the intensity of the outgoing light in the light-transmitting medium is adjusted to a specific response wavelength according to the intensity of incident light. In a light control element that performs negative control in a region, the light control element includes a voltage applying unit that applies a voltage to an optical path, and controls a response wavelength region of the light transmissive medium by a voltage applied to the optical path. Characteristic light control element for 1.5 μm wavelength band. 2. The light control element according to claim 1, wherein a plurality of said voltage applying means are provided. 3. The light control element according to claim 1, wherein a base material of said light transmitting medium is a dielectric material. 4. The light control device according to claim 3, wherein said dielectric material is a ferroelectric material. 5. An optical control composite device comprising a plurality of light control elements for a wavelength band of 1.5 μm, wherein a plurality of light control elements are connected in series, and each light control element is An optical path for allowing incident light in a wavelength band of 1.5 μm to enter and emitting outgoing light, the optical path including at least an erbium-containing light transmitting medium, and the intensity of the outgoing light in the light transmitting medium. A light control composite device, wherein the light control medium is negatively controlled in a specific response wavelength region according to the intensity of incident light, and the response wavelength regions of the respective light transmitting media in the respective light control devices are different. 6. At least one light control element includes voltage applying means for applying a voltage to the optical path, and a response wavelength region of the light transmitting medium is shifted by the voltage applied to the optical path. 6. The light control composite device according to claim 5, wherein: 7. The optical path is a bulk body made of the light-transmitting medium, and a plurality of voltage applying means are provided along a light propagation direction of the bulk body, whereby a plurality of light control units are provided in the bulk body. The light control composite device according to claim 6, wherein the device is provided. 8. The optical control composite device includes an optical waveguide substrate, wherein the optical path comprises an optical waveguide formed on the optical waveguide substrate, and a plurality of voltage application devices are provided along a light propagation direction of the optical waveguide. 7. The light control composite device according to claim 6, wherein means are provided, whereby a plurality of light control devices are provided in series. 9. The light control composite device according to claim 5, wherein each light transmitting medium forming each light path of each light control device is made of erbium and a base material different from each other.