JP2902530B2 - Optical function element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical functional device. More specifically, the present invention relates to a new optical functional element useful as an optical memory or the like necessary for performing optical logic operation and optical computing in the field of optoelectronics.

2. Description of the Related Art In recent years, the progress of optoelectronic technology has been remarkable, and its importance as a fundamental technology that opens up a new era of optical communication, optical computers, and the like has been increasing. In such a situation,
As one of the optical functional elements, an optical memory for storing optical signal information is indispensable, and methods and materials are being studied. The optical memory refers to a memory that uses light for both writing and reading of information, and in a broad sense, includes a memory that uses light for either of them. Although the importance of such optical memories is recognized, unfortunately, only analog image memories are currently in practical use, and many others are in the research stage. Among them, holographic memories, magneto-optical memories, and glass semiconductor memories are currently promising. Holographic memory is a picture of the interference of light obtained by laser light. However, this memory has the drawback that although reading is fast, writing and developing processes are required.
A magneto-optical memory is a memory in which a ferromagnetic material such as MnBi is irradiated with a laser beam to write information, and the information is read out by utilizing the Faraday effect in which polarized light is generated in transmitted light depending on the state of magnetization. However, there is a disadvantage that light and magnetism are used together. Furthermore, a glass semiconductor memory uses a phenomenon in which a glass semiconductor is irradiated with a laser beam of an appropriate intensity to cause a reversible phase transition between polycrystal and amorphous, and a change in transmittance. A memory for writing and reading information has disadvantages such as a slow switching speed of phase transition. On the other hand, studies have been made to construct an optical memory using a bistable semiconductor laser. The term “optical bistable” as used herein refers to a phenomenon in which the output intensity takes two stable states with respect to one input light intensity. However, in a bistable semiconductor laser, an optical input is used as a switch for switching from an off state to an on state. On the other hand, switching from the on state to the off state is realized because there is no negative light pulse. Not applicable (Applied Physics 58, pp. 1574 to 1583: 1
(November, 989). In general, when a semiconductor laser is operated at a high-speed pulse, a relaxation oscillation is generated in the oscillation light intensity. This relaxation oscillation phenomenon is observed in almost all types of lasers other than the semiconductor laser, and the basic physical mechanism of this phenomenon is a correlation between the oscillating electromagnetic field in the resonator and the population inversion of atoms. Increasing the field strength leads to a decrease in population inversion density through an increase in the stimulated emission rate. It also causes a decrease in gain, which in turn causes a decrease in field strength, resulting in a decrease in field strength. Therefore,
The semiconductor laser rises instantaneously upon receiving a drive current with a fast rise, but the light intensity usually fluctuates by about 1 nsec due to relaxation oscillation and reaches a constant value. For this reason, the pulse response speed is suppressed to a maximum of about 1 nsec, and a method of controlling the relaxation oscillation is being studied.
For example, the external light injection method is a method of injecting oscillation light of another laser operating in conjunction with a semiconductor laser that directly modulates, and can suppress relaxation oscillation (R. Lang and
K.Kobayashi: Suppression of the relaxation oscill
ation in the modulated output of semiconductor las
ers, IEEE J. Quantum Electron., QE-12, 3, PP194-19
9 (1976).). However, in this case, there are disadvantages that two lasers are required and their oscillation axis modes must be matched. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to solve the drawbacks of the prior art and to provide a new optical functional element that stores information of an optical signal by an electric input or an optical input. I have.

According to the present invention, there is provided an optical functional device having a light transmitting medium and a light generating element, wherein the light transmitting medium has a specific light wavelength λ _1. Shows a low transmittance, and the surrounding light wavelengths λ ₂ and λ
₃ (λ ₂ <λ ₁ <λ ₃ ), a high transmittance is exhibited, and the light-generating element has light wavelengths λ ₁ , λ
₂ and λ ₃ , and a change in the wavelength thereof produces hysteresis with respect to the current injection amount or the light irradiation amount, and the light of the light wavelengths λ ₁ , λ ₂ and λ ₃ from the light generating element is There is provided an optical functional element having a memory function of irradiating a light transmitting medium and maintaining a low intensity or a high intensity state of light transmitted through the light transmitting medium because the wavelength change has hysteresis. That is, the light generating element generates any of the light wavelengths λ ₁ , λ ₂ , or λ ₃ when a control input is externally applied electrically or optically. Controlling the wavelength of the light generated by the light generating element in accordance with the change of the control input, controlling the transmittance of the light transmitting medium by the controlled light, and the change in the wavelength causes a hysteresis with respect to the control input. Therefore, the present invention is characterized by having a memory function of maintaining a low intensity or a high intensity state of light transmitted through the light transmitting medium. As one of the means for this, in the present invention, the optical characteristics of the light transmitting medium are controlled, and for example, a proper element such as a transparent ceramic, glass, semiconductor, or insulator, a specific element such as a rare earth element Are contained in them. In addition, since the optical transition of the rare earth element is an inner shell transition, it has a characteristic that it is hardly affected by the contained base material. Then, in the optical control device of the present invention, the light transmission medium for light wavelengths lambda ₁ shows a low transmittance, so that indicates a high transmittance with respect to light wavelength lambda ₂ and lambda _3. Therefore, when the light transmitting medium to the light wavelength lambda ₁ of light is input the light is absorbed becomes OFF state, and transmitted therethrough when the light of the light wavelength lambda ₂ and lambda ₃ are input to the inverse O
It becomes N state. Also, λ ₂ to λ ₁ and λ ₁ to λ ₃
Since the wavelength change has hysteresis with respect to the control input, the OFF state and the ON state are maintained. The light generating device in such an optical functional element, when applying an electrical or optical control input from the outside, that the light generation wavelength lambda ₂ to lambda _1, or changes from lambda ₁ to lambda ₃ . That is, for example, when a semiconductor laser is used as a light generating element, the oscillation wavelength changes discontinuously in a long wavelength measurement as the amount of injected current increases, and conversely, if the amount of injection is reduced from the time of high current injection, hysteresis occurs. It is generally known that the oscillation wavelength changes discontinuously in the short wavelength measurement (M.
Nakamura, “Single mode operation of semiconductor
injection lasers ”IEEE Trons. Circuits and Syste
ms, CAS-26,1055 (1979)). Therefore,
Using a semiconductor laser, increase the current from the low injection state to the high injection state, change the oscillation wavelength from λ ₂ to λ ₁ , and return to the low injection state again, the oscillation wavelength has hysteresis with respect to the injection current Therefore, λ ₁
, And a low transmittance state (that is, an OFF state) is maintained. Further, when the oscillation wavelengths λ ₁ and λ ₃ are generated in the low injection state and the high injection state, respectively, the same principle is applied, and even if the oscillation wavelength is returned to the low injection state again, the λ ₃
And maintains a high transmittance state (that is, an ON state) to perform a memory function. further,
When the memory function of the present invention is used, the influence of the relaxation oscillation which causes the deterioration of the pulse drive switching speed of the semiconductor laser can be eliminated, and the high-speed switching operation can be performed. That is, for example, when the current of the semiconductor laser is changed from O or a low injection state to a high injection state and the oscillation wavelength is changed to λ ₁ , even if the current injection amount slightly changes (relaxation oscillation), the λ ₁ is reduced by the hysteresis effect. Maintain the oscillation wavelength. Therefore, even if relaxation oscillation occurs in light intensity, a change in intensity due to the relaxation oscillation can be eliminated by transmitting the light transmitting medium. That is, the switching time of the optical function element is determined only by the rise time of the semiconductor laser, and a high-speed switching operation is realized. Further, in order to reduce the size of the optical functional device of the present invention, a light transmitting medium is formed in the resonator of the semiconductor laser light generating device. In this way, the laser light is reflected many times into the resonator and is absorbed by the light transmitting medium each time, so that the effective light transmitting medium length can be increased, and the light transmitting medium It is possible to make the optical function element thinner, and the optical function element can be downsized. Further, as one method of connecting the optical functional elements of the present invention in multiple stages, a light receiving element such as a phototransistor or a photodiode is provided in addition to the optical functional element. By doing so, the light signal from the preceding stage is received by the light receiving element,
Multistage connection can be achieved by using the output current as the injection current of the light generating element. As described above, in the case of the optical functional device of the present invention, the optical functional device ( O ) due to the inversion in the optical nonlinear absorption and the longer wavelength (red shift) of the semiconductor laser is used.
pticaldevices by r ed-sift
of diode laser and i nvers
ion in o optical n onlineara
bsorption: ORION). Hereinafter, the present invention will be described in more detail with reference to Examples.

【Example】Example 1 FIG. 1 shows an optical functional device of the present invention and its function.
1 is a diagram illustrating an example of a device configuration. Where the light transmitting medium
(10) is erbium: Er as a rare earth element³⁺Including
Yttrium Aluminum Garnet (YAG)
Using a rod of φ3 mm x 3 mm consisting of
Is 50 at% ｛, that is, (Er_0.5Y_{0. Five})_ThreeAl_FiveO
₁₂｝ Semiconductor laser functioning as light generating element
The element (11) includes a drive control circuit (12) and a temperature controller.
By driving by (13), the laser of a certain wavelength
The light is output, and E is output through the beam splitter (14).
r: Inject laser light into light transmitting medium (10) made of YAG
I try to shoot. Through the light transmitting medium (10)
The optical output is received by the photodetector (15) and digitized.
Guoscilloscope (16) and Optical Spectroanalyse
Observed at the (17). In such a configuration, FIG.
(A) is a change in current injected into the semiconductor laser element (11).
FIG. 2 (b) shows the laser output at that time digitized.
This shows the change in light intensity observed with the oscilloscope (16).
It was done. FIG. 2C shows the light of Er: YAG.
The change in light intensity after transmission through the transmission medium (10) was shown.
Things. Adjust the temperature controller to adjust the temperature of the laser head.
The temperature was kept constant at 33 ° C. Compare FIG. 2 (b) and FIG. 2 (c)
Then, the semiconductor laser device (11) shown in FIG.
As shown in FIG. 2 (c), the change in output light intensity
Inversion after transmission through excess medium (10) (low light intensity state)
And perform its memory function to keep its low light intensity state
You can see that there is. This phenomenon is shown in FIGS. 3 and 4.
Is also confirmed. FIG. 3A shows a semiconductor laser device (1).
The current to be injected in 1) is increased from 54 mA to 3 mA by 99 mA.
The optical spectroanalyzer shown in Fig. 1
This shows the relationship between the light wavelength detected by the
FIG. 3B shows an optical spectrum after transmission through the light transmitting medium (10).
It is a detection result of a Kuro analyzer. FIG. 4 (a)
Means that the current injected into the semiconductor laser element (11) is 99 m
When the current is reduced from A to 54 mA in 3 mA steps,
It shows the relationship between the light wavelength detected by the Kuro analyzer and the intensity.
FIG. 4B shows the state after transmission through the light transmitting medium.
It is a detection result. As shown in FIG.
The light wavelength from 786.1 nm at 78 mA
It can be seen that it changes discontinuously to 787.5 nm. Figure
4 (a), conversely, when the injection current is reduced, 60 mA
At a light wavelength of 787.5 nm to 786.1 nm
It can be seen that it changes discontinuously in FIG. FIGS. 3A and 4
From (a), it can be seen that the change in optical wavelength
It turns out that there is cis. 3 (b) and FIG.
(B) The laser light after transmitting through the light transmitting medium is 78
Light having a wavelength of 7.5 nm is absorbed by a light transmitting medium.
I understand. 3 (b) and 4 (b)
In the case of 75 mA injection current
And a strong light intensity is observed in FIG.
In 4 (b), the light intensity is almost zero.
You. Therefore, as shown in FIG.
A (at low carrier injection) and 99 mA (high carrier injection)
) Control input to the semiconductor laser and its optical output
(FIG. 2B) is irradiated on the light transmitting medium, and the transmitted light is observed.
When measured, a light intensity output having a memory function as shown in FIG.
Power is gained. In other words, the change in light wavelength with respect to the injection current
Due to the existence of hysteresis,
Once the carrier wavelength is changed by injecting high carriers once,
The optical wavelength remains high even after returning to the low carrier injection state.
Hold the state and let this laser light pass through the light transmitting medium
Thus, a memory function for maintaining a low strength state is exhibited. FIG.
Is the light absorption spectrum of the light transmitting medium (Er: YAG)
is there. According to FIG. 5, 787.3 nm is the absorption peak.
This is the Er: YAG³⁺Excitation absorption (^TwoH
_11/2−^FourI_13/2).Example 2 Laser head using the same semiconductor laser as in the first embodiment
If the temperature is kept constant at 43 ° C,
Injection currents of 75 mA and 99 mA are applied to the semiconductor laser.
, The 787.5 nm and 789.6 nm, respectively,
An oscillation wavelength was observed. In a configuration similar to FIG.
6 (a) shows a change in current injected into the laser element, and FIG.
6B shows the light output intensity, and FIG. 6C shows Er: YAG.
It shows a change in light intensity after transmission. FIG.
6B and FIG. 6C, the light shown in FIG.
Note that the intensity maintains the high light intensity state in FIG.
You can see that it works. FIG. 7 and FIG.
It is a measurement result of a Kuro analyzer. FIG. 7A shows injection.
The current was increased from 54 mA to 99 mA in 3 mA increments.
FIG. 7B shows the result after passing through the light transmitting medium.
You. FIG. 8 (a) shows that the injection current is reversed from 99 mA to 3 mA.
FIG. 8 (b) shows the result of reducing the
This is the result after transmission through the transmission medium. As shown in FIG.
As the current increases, the light wavelength becomes 78 at 81 mA.
It changes discontinuously from 7.5 nm to 789.6 nm
I understand. From FIG. 8A, conversely, the injection current is reduced.
The light wavelength changes discontinuously at 69 mA
You can see that FIG. 7A and FIG.
That there is hysteresis for injection current
You. 7B and FIG. 8B, the light transmitting medium is transparent.
The laser light after passing, the light of the light wavelength of 787.5 nm is
Absorbed by the light transmitting medium, and the light of 789.6 nm is transmitted.
I understand. Therefore, as shown in FIG.
Input current 75 mA (at low carrier injection) and 99 mA (high
Control input during carrier injection) is input to the semiconductor laser.
The light output of FIG. 6 (b) is applied to the light transmitting medium,
Observation of over-light keeps high intensity state as shown in Fig. 6 (c)
Exercise memory function. It is clear from the above results
2 and 6, the light output is Er: YAG light.
By transmitting the light through the transmission medium, low light intensity and
Memory function to maintain high light intensity state
It is.Example 3 FIG. 9A shows that the oscillation wavelength is about 78 for an injection current of 99 mA.
Set to 7.5 nm, 99 mA monomorphic pulse
Is the input waveform in the case where is formed. Laser-specific relaxation
A sum oscillation is observed. FIG. 9B shows the result after passing through Er: YAG.
FIG. The point to note here is in FIG.
That the second and subsequent peaks of the relaxation oscillation are suppressed
It is. This is a light wave whose oscillation wavelength is constant at the first rise.
Length, for example λ₁(787.5 nm)
Even if the intensity changes due to movement, λ
₁Light wavelength and is absorbed when transmitted through the transmission medium.
It is. Therefore, the relaxation oscillation is suppressed, and the rise time is almost
High-speed operation is possible with only switching time. By the way
In this experiment, the switching time was about 100ps.
is there. For reference, FIG. 10A shows the temperature of the laser head.
Adjust the degree to 786 nm (λ ₁Set to light wavelength
FIG. 1 shows a single-pulse input waveform of 99 mA.
0B is an output waveform after transmission through the light transmission medium. This figure 1
10B, the input light of FIG.
It can be seen that the influence of the relaxation oscillation appears. Rice cake
In the above example, the rare earth element contained in the light transmitting medium
The element is Er ⁺³, But is not limited to this.
Absent. Appropriate selection according to the wavelength of light, the type of light transmitting medium, etc.
Selected.

As described in detail above, an optical memory can be constituted by the optical functional device of the present invention. This optical memory is switch-off type (low light intensity state) with respect to a control input by selecting an optical wavelength. ) And the switch-on type (high light intensity state).
Further, at the time of switching of this optical function element, high-speed operation is possible without being affected by relaxation oscillation.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an optical functional device of the present invention and a device configuration for measuring its function.

FIGS. 2A, 2B and 2C are diagrams respectively showing an injection current to a semiconductor laser device as an example, an output light thereof and an intensity change of light after passing through a light transmitting medium.

FIGS. 3A and 3B are correlation diagrams of light wavelength and intensity when an injection current is increased as an example.

FIGS. 4A and 4B are correlation diagrams between an optical wavelength and an intensity when an injection current is reduced, as an example.

FIG. 5 is a light absorption spectrum diagram of a light transmitting medium as an example.

FIGS. 6A, 6B, and 6C are diagrams showing the change in the intensity of the current injected into the semiconductor laser element, the output light thereof, and the light transmitted through the light transmitting medium, as examples.

FIGS. 7A and 7B are correlation diagrams of light wavelength and intensity when an injection current is increased, as an example.

FIGS. 8 (a) and (b) are correlation diagrams between the light wavelength and the intensity when the injection current is reduced, as an example.

FIG. 9 is an output waveform diagram of a single pulse.

FIG. 10 is an output waveform diagram of a single pulse.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Light transmission medium 11 Semiconductor laser element 12 Drive control circuit 13 Temperature controller 14 Beam splitter 15 Photodetector 16 Digitizing oscilloscope 17 Optical spectroanalyzer

Claims (7)

(57) [Claims] 1. An optical functional element having a light transmitting medium and a light generating element, wherein the light transmitting medium has a low transmittance at a specific light wavelength λ ₁ and surrounding light wavelengths λ ₂ and λ _3. (Λ ₂ <λ
₁ <λ ₃ ), a high transmittance is exhibited, and the light generating element generates light of light wavelengths λ ₁ , λ ₂ , λ ₃ depending on the amount of current injection or light irradiation, and the wavelength change is based on the amount of current injection or light irradiation. Light from the light generating element is irradiated with the light having the wavelengths λ ₁ , λ ₂ , λ ₃ from the light generating element, and the light transmitting medium is subjected to the hysteresis in the wavelength change. An optical function element having a memory function of maintaining a low or high intensity state of transmitted light. 2. A semiconductor laser is used as a light generating element. This semiconductor laser can inject carriers into an active region by current or light irradiation, and the light wavelength changes from λ ₂ to λ ₁ when a low carrier is injected to a high carrier. However, when returning to the low carrier injection mode, the light wavelength of λ ₁ is maintained, and the light intensity transmitted through the light transmitting medium is maintained in a low intensity state, or when the low carrier injection is performed and the high carrier injection is performed, the light wavelength is changed. lambda ₁ changes to lambda ₃ from holding the _third light wavelengths lambda and returned again in the low carrier injection, an optical functional device according to claim 1 for holding the light intensity transmitted through the light transmitting member to a high strength state. 3. The light according to claim 1, wherein the light transmitting medium is a material selected from the group consisting of transparent ceramics, glass, semiconductors and insulators, containing at least one rare earth element. Functional element. 4. A light transmitting medium containing a rare earth element erbium Er ³⁺ , wherein the light wavelength λ ₁ of low transmittance is reduced by excitation absorption ( ² H _11/2 −) of the erbium element Er ^3+.
4. The optical functional device according to claim 1, which is near an absorption peak of ⁴ I _13/2 ). 5. The light transmitting medium is a transparent ceramic Y.
5. The optical functional device according to claim 1, wherein the rare earth element erbium Er ³⁺ is contained in AG (yttrium aluminum garnet). 6. A light-transmitting medium or a light-generating element according to claim 1, wherein light-intensity fluctuation due to relaxation oscillation generated during laser oscillation is suppressed, and high-speed operation is performed. An optical functional element. 7. The optical transmission element according to claim 1, 2, 3, 4, 5 or 6, wherein the light transmitting medium is provided in a resonator of the semiconductor laser light generating element in order to reduce the size and connect the optical function element in multiple stages. An optical functional element, wherein a light receiving element such as a phototransistor or a photodiode is formed in addition to the optical functional element.