CA2093538C - Optical device - Google Patents
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- CA2093538C CA2093538C CA002093538A CA2093538A CA2093538C CA 2093538 C CA2093538 C CA 2093538C CA 002093538 A CA002093538 A CA 002093538A CA 2093538 A CA2093538 A CA 2093538A CA 2093538 C CA2093538 C CA 2093538C
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Abstract
An optical controlling device has a light transmitting medium showing a low transmittance for specific light wavelength .lambda.1 and a high transmittance for light wavelength .lambda.2 around said light wavelength .lambda.1, and a light emitting device emitting a light of light wavelength .lambda.1 or .lambda.2, and controls light intensity in accordance with changes in a controlled light through light irradiation and light transmission.
An optical functional device has a light transmitting medium showing a low transmittance for specific light wavelength .lambda.1 and a high transmittance for light wavelengths .lambda.2 and .lambda.3 around said wavelength .lambda.1 (.lambda.2 < .lambda.1 < .lambda.3), and a light emitting device changing wavelength while accompanying a generation of hysteresis dependent upon the quantity of current infection or light irradiation, and emitting a light having light wavelength .lambda.1, .lambda.2 or .lambda.3. A light intensity transmitting through said light transmitting medium is maintained at a low-intensity or high-intensity state under the effect of said hysteresis, thereby a memory function is obtained.
An optical functional device has a light transmitting medium showing a low transmittance for specific light wavelength .lambda.1 and a high transmittance for light wavelengths .lambda.2 and .lambda.3 around said wavelength .lambda.1 (.lambda.2 < .lambda.1 < .lambda.3), and a light emitting device changing wavelength while accompanying a generation of hysteresis dependent upon the quantity of current infection or light irradiation, and emitting a light having light wavelength .lambda.1, .lambda.2 or .lambda.3. A light intensity transmitting through said light transmitting medium is maintained at a low-intensity or high-intensity state under the effect of said hysteresis, thereby a memory function is obtained.
Description
z~~~~ ~~
OPTICAL DEVICE
FIELD OF THE INVENTION
The present invention relates to an optical device.
More particularly, the present invention relates to an optical controlling device useful fox a photo inverter and an optical functional device useful for an optical memory, both of which are indispensable for optical logical calculations and light computing in the photoelectronic field.
PRIOR ART
A photoelectronic technology has recently made a remarkable progress and is becoming a more important fundamental technology for an optical communication, an optical computer and the like.
Under these circumstances, an optical control method of performing logical culculations of a computer by means of optical signals has been studied as one of the control techniques for utilizing a light.
In the photoelectronics field including an optical communication and an optical information processing, for example, some researches are made on a control of a controlled light by a controlling light. According to this method, it is possible to achieve a switching operation higher in speed than that of an electrical switching circuit. It also permits multiple parallel processing operations by using an imaging ability of a light. The method is, therefore, considered to be N ~~ ~ ~ e! ti useful in the optical integrated circuit, for example.
An optical device using nonlinear optical effects is, on the other hand, studied for the purpose of an optical control.
While wavelength conversion effect such as a generation of a second higher harmonic has conventionally been considered to be important for the practical use, general attentions are now particularly directed toward an alteration of retractive index dependent on the light intensity and a change of absorption coefficient (Applied Physics, 59, 155-163 (February 1990)).
However, since these effects take place in a tertiary polarization, a nonlinear optical material having a higher-order polarization effect is required ["Degenerate fourwave mixing in semiconductor-doped glasses," J. Opt. Soc. Am., T3, 64?-653 (May 1983)]. Although an absorption-saturated type bistable semiconductor laser is considered to be most useful for a semiconductor optical control device, an optical input is employed for switchover from off-state to on-state, whereas a negative optical pulse does not exist for switchover from on-state to off-state (NOT circuit). Therefore, the bistable semiconductor laser has not been practically used (Applied Physics, 58, 15?4-1583 (November 1989)). The words "optical bistability" described herein means a phenomenon in which two stable states of output intensity are available for a single light intensity.
An optical memory is, on the other hand, becoming essential, which stares optical signal informations. The optical memory refers to a memory using a light when writing and reading informations, In a wide sense, however, it includes a memory using a light while either.
Although such optical memory is generally recognized to be important, only an analog imaging memory is currently utilized, and many others are still in the stage of research.
There are a holographic memory, a photomagnetic memory and a glass semiconductor memory which are considered to be more available among those. The holographic memory is a photograph of the optical interference given by a laser beam. This memory is, however, defective in that, while it allows a high-speed reading, it requires the writing and developing operations.
The photomagnetic memory is a memory which allows writing of informations by irradiating a laser beam to a ferromagnetic material such as MnBi arid reading of the informations by employing a Faraday effect in which polarization of a transmitting light is generated dependent upon the magnetization state. It is, however, defective in that light and magnetism are employed in parallel.
The glass semiconductor memory is a memory which permits writing and reading of informations by using a phenomenon in which the irradiation of a laser beam having an appropriate intensity to the glass semiconductor leads to a reversible phase transfer between polycrystalline and non-crystalline states, and transmittance is changed. Tt has, however, problems in that the switching speed of phase transfer is slow.
On the other hand, some researches have been performed in which an optical memory is designed by the bistable ~~~93 ~~8 semiconductor laser. This type of the memory, however, has not yet been practically attained because of similar problems mentioned in the above.
Generally, it is also known that a high-speed pulsation of the semiconductor laser produces relaxation oscillation in the intensity of the emitted light. This relaxation oscillation is observed in almost all kinds of laser, and the basic physical mechanism of this phenomenon is an interactive function between the electromagnetic field oscillated in the oscillator and the reversal distribution of atoms. An increase of the field intensity leads to a decrease of the reversal distribution density through an increase in induced emission factor. This, in turn, brings about a decrease in gain and then a decrease in the field intensity.
Although the semiconductor laser instantaneously rises up upon a fast-rising driving current, light intensity usually varies by about 1 nsec under the subsecquent relaxation oscillation until a certain value is reached. The pulse response speed is, therefore, limited to about 1 nsec on the maximum, and some studies are performed to control the relaxation oscillation.
An external light injection method is well-known in which a light is injected into a semiconductor laser conducting a direct modulation from another laser working in conjuction with the one. The external light injection suppresses relaxation oscillation (R. Lang and K. Kobayashi: Suppression of the relaxation oscillation in the modulated output of I
semiconductor lasers, IEEE J. Quantum Electron., QE-12, 3, 194-199 (1976)). xowever, this method is defective in that two lasers are needed and the oscillating axis modes ' thereof must be in correspondence with each Qther. ;
The present invention has an object to provide an optical device indispensable for carrying dut optical logical calculations and optical computing in the phatoalectronia field.
i More particularly, an object of the present invention is to provide an optical controlling device which aylows !
switching of an optical signal from on-state to off-i state, i.e., an optical SOT circuit, and permits full-optical logical calculations.
a Another object of the present invention is to provide an !
optical functional device which stores optical signal information through an electrical or optical input. , Therefore, in accordance with the present invention, there is provided an optical controlling device comprising a light transmitting medium showing a low transmittance far specific light wavelength ~i and a high transmittance for light wavelength ~Z around said i wavelength ~1, and a light emitting device emitting a light having light wavelength ~1 or ~~, wherein said !
optical controlling device controls light intensity in accordance with the emitted light having wavelength ~1 or ~2 thrbugh irradiation from said light emitting device and transmission of the emitted light through said light transmiting medium.
S
Also in accordance with the present invention, there is provided an optical controlling device comprising a light .
transmitting medium showing a low transmittanGe ~or specific light wavelength ~1 and a high txansmittance for light wavelength ~z around said wavelength ~l, and a light , emitting device emitting a light having wavelength ~1 or ~z, wherein said optical controlling device controls light intensity in accordance with the emitted light having wavelength ~1 or ~2 through irradiation from said light .
emitting device and transmission of the emitted light ;
through said licht transmitting medium, wheroin said light emitting device is a semiconductor laser, said semiconductor laser respectively emitting wavelengths ~Z and ~~ at a low- , current and a high-current in5ections, or respectively emitting wavelengths ~l and ~2 at a low- ;
current and a high-current injections. , Further in accordance with the present invention, there is provided an optical controlling device comprising a ' light transmitting medium showing a low transmittance for specific light wavelength ~1 and a high transmittance for light wavelength ~2 around said wavelength ~~, and a light , emitting device emitting a light having wavelength ~~ or i ~2, wherein said optical controlling device controls light , intensity in accordance with the emitted light having wavelength ~1 yr ~2 through irradiation from said light emitting device and transmission of the emitted light through said light transmitting medium, wherein said light transmitting medium comprises a substance selected from the group consisting of , transparent ceramics, a glass, a semiconductor and 5a an insulator, said substance having added thereto at least one rare earth element, wherein said at least one rare earth element is erbium, Er3+
, wherein said light wavelength 7~1 for which said light transmitting medium k~as a low transmittance is near an excited absorption peak (zHll~2-4I13,z) of erbium, Erg' . i Still further in accordance with the present inven,ti.vr~, there is provided an optical controlling device , comprising a light transmitting medium showing a low transmittance for specific light wavelength ~,1 and a high transmittanoe for light wavelength ~,2 arouxzd sa:Ld , wavelength 7~1, and a light emitting device emitting a , light having wavelength 7~1 or ~,Z, wherein said optical controlling device controls light intensity in accordance with the emitted light having wavelength ~,1 or 7~2 through , irradiation from said light emitting device and transmission of the emitted light through said light transmitting medium, ' wherein said light transmitting medium comprises a substance selected from the group oonsisting of transparent ceramics, a glass, a semiconductor and an insulator, sand substance havixlg added thereto at least one rare earth element, i wherein said at least one rare earth element is erbium, ~x3+ .
wherein said light transmitting medium is composed of transparent ceramics of YAG (yttrium-aluminum-garnet) with added erbium, Er3', wherein said light wavelength 7~1 for which said light , transmitting medium has a low transmittance is near 5b an excited absorption peak ~2Isa11/2-a~.13/1~ of erbium, Er3+. , Still further in accordaz~oe with the present invention, .
there is prow ded an optical functional device comprising a light transmittixzg medium showing a low tr&nSmittaYiCe for specific light wavelength ~t,l aY~d high transmittance , for' light wavelengths ~.2 and ~.g around said wavelength a,1 (~z ~~1 ~~3 ) , and a light emitting device changing wavelength while accompanying a generation of hysteres~.s dependent upon the quantity of cuxxent injection or light .
irradiation, and emitting a light having light wavelength i ~1. ~.2 or ~3 wherein a light of wavelength ~,1, J~z or ~3 is ~xrad~.a.ted from $aid light emitting device to said light transmitting medium, the intensity o~ said light transmitting through said light transmitting medium is , maintained at a low or high state under the effect of said hysteresis, thereby a memory function is obtainad.
This and other objects, features and advantages of the invention will beCOrne more aLbparent upon reading of thA
following detailed specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an embodiment of ;
the optical controlling device and the device for measuring its functions; , FIGS. 2a, 2b and 2c are respectively correlation diagrams illustrating the electric cuxrent injected to a i semiconductor laser cle~erice., the light intensity of the output light of the semiconductor laser device, and the optioal , 5c ~~~~~o intensity after transmission through a light transmitting medium;
Fig. 3 is a correlation diagram between the injected current to the semiconductor laser device and the light transmittance;
Fig. 4 is a correlation diagram between the injected current to the semiconductor laser device and the light intensity;
Fig. 5 is a diagram of the light absorption spectrum of the light transmitting medium;
Fig. 6 is a block diagram illustrating another embodiment of the optical controlling device and the device for measuring its functions;
Fig. 7 is a correlation diagram between the laser intensity and the transmittance;
Fig. a is a block diagram illustrating an embodiment of the optical functional device and the device for measuring its functions;
Figs. 9a, 9b and 9c are respectively correlation diagrams illustrating the injected current to a semiconductor laser device, the light intensity of the output light and the light intensity after transmission through a light transmitting medium;
Figs. 10a and lOb are respectively correlation diagrams between light wavelength and intensity when increasing the injected current;
Figs. 11a and 11b are respectively correlation diagrams ~?i)~3 ~~8 between light wavelength and intensity when decreasing the injected current;
Fig. 12 is a diagrm of the light absorption spectrum of the light transmitting medium;
Figs. 13a, 13b and 13c are respectively correlation diagrams illustrating the injected current to the semiconductor laser device, the light intensity of the output light, and the light intensity after transmission through the light transmitting medium;
Figs. 14a and 14b are respectively correlation diagrams between light wavelength and intensity when increasing the injected current, respectively;
Figs. 15a and 15b are respectively correlation diagrams between light wavelength and intensity when decreasing the injected current;
Fig. 16 illustrates output waveforms of single-shaped pulses; and Fig. 1T illustrates another output waveforms of single-shaped pulses.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an optical controlling device which comprises a light transmitting medium showing a low transmittance for specific light wavelength ~1 and a high transmittance far light wavelength ,~2 around said wavelength ,~1, and a light emitting device emitting a light having light - T -~~~3a~~
wavelength ,~1 or ,~2, wherein said optical controlling device controlls light intensity in accordance with changes in a controlled light through light irradiation of said controlled light having wavelength ,~1 or ,~2 from said light emitting device and light transmission of the controlled light through said light transmitting medium.
A light emitting device of the optical controlling device emits a light of either light wavelength ,~1 or ,~2 by applying an external electrical or optical controlling input.
The transmittance of a light transmitting medium is controlled by means of the controlled light.
In the present invention, light properties of the light transmitting medium are controlled for accomplishing the light control, and a specific element including, for example, a rare earth element is added to an appropriate material such as transparent ceramics, a glass, a semiconductor or an insulator.
A rare earth element optically shows the inner shell transition so that it is hardly affected by the base material. By adding this rare earth element as a doping element to the light transmitting medium, it is possible to generate a ground absorption from the ground level E1 to the excited level E3 and an excited absorption from the metastable level E2 to the excited levEl E4 for the light of ,~l (E4 > EZ > E3 > E1)' Therefore, the transmittance at light wavelength ,~1 is considerably reduced.
On the other hand, when a controlling input is electrically or optically entered in the light emitting device, _ g _ N~~JO~d the emitted wavelength varies from ,~1 to ,~2, or from ,~2 to ,~1, For example, it is generally known that, when using a semiconductor laser as a light emitting device, the emitted wavelength discontinuously varies toward longer wavelength, as the quantity of the injected current increases (M. Nakamura, "Single mode operation of semiconductor injection lasers," IEEE
Trons. Circuits and Systems, CAS-26, 1055 (19T9)j. If oscillated wavelength varies from ,~2 to ,~1 when the injected current to the semiconductor laser is increased, the light intensity of ,~1 becomes bigger than that of a2 because of the larger quantity of the injection. However, when the output of the semiconductor laser is irradiated to the above-mentioned light transmitting medium, light output of ,~1 becomes smaller than that of ,~2 because the transmittance of light wavelength ,~1 is lower than that of ,~2, thus achieving an optical NOT circuit.
In the present invention, since the light transmitting medium exhibits a low transmittance for light wavelength ,~1 and a high transmittance for ,~2, respectively, a light having light wavelength ,~1 is absorbed when the light is entered in the light transmitting medium, thus the off-state being achieved. The on-state is given by transmission of a light having light wavelength ,~2 when the light is entered. Further, since it is possible to dope an element which generates the excited absorption for the light of wavelength ,~1, the excited absorption which has a higher degree of absorption than the ground absorption takes place, and as a result, the -N(~~3W~
transmittance of ,~1 transmitting through the light transmitting medium is considerably reduced according to the excited absorption. The difference of the transmittance between the light of ~1 and the one of ,~2 each of which transmits through the light transmitting medium becomes remarkable, thus enabling to obtain an optical inverter (NOT circuit) having a large ratio ON/OFF. Combining a plurality of the optical inverters enables to make up any logical circuit (NOR, XOR, for example). It is thus possible to achieve optical logical calculations and optical computers by using the optical controlling device of the present invention as a key device.
The present invention also provides an optical functional device which comprises a light transmitting medium showing a low transmittance for specific light wavelength ,~1 and a high transmittance for light wavelengths ,~2 and ,~3 around said wavelength ,~1 (,~~ < ,~1 < ,~3), and a light emitting device changing wavelength while accompanying a generation of hysteresis dependent upon the quantity of current injection or light irradiation, and emitting a light having light wavelength ~1' ~2 °r ~3~ wherein a light of wavelength ,~1, ,~2 or ,~3 is irradiated from said light emitting device to said light transmitting medium, the intensity of said light transmitting through said light transmitting medium is maintained at a low or high state under the effect of said hysteresis, thereby a memory function is obtained.
A light emitting device in this optical functional - l0 -~'f~~3u3~
device emits a controlled light of either light wavelength ,~1, or ,~3 though entering an electrical or optical controlling input. The transmittance of the light transmitting medium is controlled by the controlled light and the intensity of the light transmitting through the light transmitting medium is maintained at a low or high state because the change of wavelength has hysteresis against the controlling input. And then, a memory function is realized.
In the present invention, optical properties of the light transmitting medium are controlled as in the case of the above-mentioned optical controlling device, and a specific element such as a rare earth element is added to an appropriate material such as transparent ceramics, a glass, a semiconductor or an insulator. Consequently, the light transmitting medium exhibits a low transmittance for light wavelength ~1 and a high transmittance for light wavelengths ,~2 and ,~3. When a light of wavelength ,~1 is entered into this light transmitting medium, the light is absorbed to give the off-state, and the entry of a light of wavelength ,~2 or ,~3 realizes the on-state through the transmission of the light. Further, since wavelength change from ,~2 to ~1 , or from ,~1 to ,~3 has hysteresis against the controlling input, the off-state and the on-state are maintained.
On the other hand, when the controlling input is electrically or optically entered in the light emitting device, the emitted wavelength varies from ,~2 to ,~1, or from ,~1 to It is generally known that, when a semiconductor laser is used ~'i1~3 ~3 as a light emitting device, decrease of the amount of the current injection from the large quantity state produces a discontinuous change in the oscillated wavelength toward short wavelength side while accompanying hysteresis (M. Nakamura, "Single mode operation of semiconductor injection lasers," IEEE
Trons. Circuits and Systems, CAS-26, 1055 (19?9)). When a current is increased from a low injection state to a high state in that semiconductor laser, oscillated wavelength is changed from ~2 to ,~1, and then the low injection state is resumed, the oscillated wavelength ,~1 is maintained and the low transmittance state (i.e., off-state) is also maintained even at the recovered low injection state. This is because the oscillated wavelength has hysteresis against the injected current. Similarly, when oscillated wavelengths ~1 and ,~3 are respectively produced at the low and high injection states, the oscillated wavelength ,~
is maintained and the high transmittance state (i.e., on-state) is also maintained even at the returned low injection. This permits achievement of a memory function.
Hy using this memory function, it is possible to eliminate the harm of relaxation oscillation which is one of the causes to deteriorate the pulse-driven switching speed of a semiconductor laser, thus permitting a high-speed switching operation. For example, when the current of a semiconductor laser is changed from null or a low injection state to a high injection state to produce oscillated wavelength ~1, the oscillated wavelength of ,~1 is maintained under the hysteresis effect even upon a slight change in the quantity of the injected ~U5'3 i~~
current (relaxation oscillation). Even if relaxation oscillation takes place in terms of the light intensity, therefore, the change in the intensity accompanied by the relaxation oscillation can be eliminated by transmitting through the above-mentioned light transmitting medium. The switching time of the optical functional device is limitted by only the rising time of the semiconductor laser, thus permitting achievement of a high-speed switching operation.
The optical functional device may be arranged in a resonator of a semiconductor laser beam emitting device, for example. In this case, the laser beam is repeatedly reflected in the resonator and is absorbed by the light transmitting medium every reflection. This enables to lengthen an effective length of the light transmitting medium and to be made up the light transmitting medium of a thin film, thus permitting downsizing of the optical functional device. In the optical functional device, furthermore, a multistage connection is possible. A conceivable method for this multistage connection would be proposed in which a light-receiving device such as a phototransistor or a photodiode is connected to the optical functional device. The light-receiving device would receive a light signal from the preceding stage, so that the output current therefrom can be used for the injection current for the light emitting device and the multistage connection is realized.
The optical functional device makes it possible to achieve an optical memory. The optical memory enables to make up any of the switch-off type (low light intensity state) and ~~~35~$
the switch-on type (high light intensity state) relative to the controlling input by selecting light wavelength. When switching the optical functional device, there is no harm of relaxation oscillation, permitting a high-speed operation.
The optical controlling and functional devices of the present invention may be referred to Optical logic devices by red-shift of diode laser and inverter of optical nonlinear absorption: ORION.
In Fig. 1, a rod having a size of ~ 3 mm x 3 mm composed of yttrium-aluminium-garnet (YAG) added erbium (Er3*) therein was employed as a light transmitting medium (10). The Er concentration was 50 at.%.
A semiconductor laser device (11) as a light emitting device was driven by a drive control circuit (12) and a temperature adjuster (13j to generate a laser beam having a constant wavelength, which was irradiated into the light transmitting medium (10) composed of the Er:YAG through a beam splitter (14) and a condenser lens (15).
The light output through the light transmitting medium (10) was received by a light detecting device (16) and was observed by means of a digital oscilloscope (1T) and a light power meter (18). The results are shown in Figs. 2 and 3.
Comparison of Figs. 2b and 2c reveals that the values of light intensity B and C of the output from the semiconductor laser device (11j which are shown in Fig. 2b were reversed, as ~i#q3~ ~~
shown in Fig. 2c, after transmitting through the light transmitting medium (10). This phenomenon can be also confirmed in Fig. 3. At the point D of Fig. 3, the transmittance considerably decreases to about a third.
Using a spectroscope (19) shown in Fig. 1, changes of wavelength of the laser output relative to the injected current of the semiconductor laser device (11) were measured. The results are shown in Fig. 4. In Fig. 4, black circles represent values of light detection intensity when wavelength of the spectroscope (19) was set at T8T nm, and the white circles repreaent those observed when wavelength was set at T84.5 nm.
At the paint E (T3 mA) in Fig. 4, the light intensity of T84.5 nm sharply decreases while the light intensity of TeT nm considerably increases. This suggests that, as a result of increase of the injected current to the semiconductor laser device (11), the center oscillated wavelength discontinuously changed at the point E from T84.5 nm to T8T nm. The value of the infected current at this discontinuous point E corresponds with the value of in3ected current at the point D of Fig. 3. As is clear from Fig. 5, furthermore, the absorption peak for the light transmitting medium (10) was at T8T nm, this corresponding with the excited absorption (2E11/2 4113/2) °g Er3* in Er:YAG.
As is evident from the results as described above, the phenomenon shown in Fig. 2, in which the light output is reversed by transmission through the Er:YAG light transmitting medium (10), is easily understood.
~'~~3W8 In Fig. 6, a i~~ 3 mm x 25 mm Er:YAG rod was employed as a light transmitting medium (10), having an Er concentration of 16 at . 9b .
A semiconductor laser device (11) as a light emitting device was driven by a drive control circuit (12) to produce.a laser beam of a center wavelength of T87 nm, which was irradiated into the Er:YAG light transmitting medium (10) through a beam splitter (14) and a condenser lens (15). This laser beam was received by a light detecting device (10j, and the light intensity was measured by an optical power meter (18) to calculate the transmittance. The results are shown in Fig.
T.
The in3ected current to the semiconductor laser device (11) was constantly set at 99 mA, and the laser beam intensity was varied through an automatic rotary ND (neutral density) filter (20).
Fig. ~ demonstrates that the value of transmittance at the point B is about twice as high as those at the points A and C. It is thus confirmed that the change of the laser beam intensity from at the point A to at the point B brings about a high transmittance state (light switch-on), and the one from at the point B to at the point C brings about a low transmittance state (light switch-off).
It is also confirmed that the effect in which the tranamittance dicreases (from the point B to the point C) against the increase of the light intensity improves the on/off ~?i~~3~~~
ratio of the inverter shown in 8xample 1.
a~ "..,.,t ., ,.
In Fig. 8, a rod having a size of ~ 3 mm x 3 mm composed of yttrium-aluminium-garnet (YAG) doped erbium (Er3~) was employed as a light transmitting medium (10). A concentration of Er was set at 50 at.%, i.e., a composition of (Er0.5Y0.5)3A15~12' A semiconductor laser device (11) as a light emitting device was driven by a drive control circuit (i2) and a temperature adjuster (13) to generate a laser beam of a constant wavelength, which was irradiated into the light transmitting medium (10) of Er:YAG through a beam slitter (14).
The output light transmitting through the light transmitting medium (10) was received by a light detecting device (15) and was observed by means of a digital oscilloscope (10) and an optical spectroanalyzer (1~). The laser head was heated and constantly kept at 33°C by the temperature adjuster (13). The results are shown in Fig. 9.
Comparison of Figa. 9b and 9c reveals that a change of the light intensity of the output from the semiconductor laser device (11) of Fig. 9b is reversed (a low light intensity state) after transmitting through the light transmitting medium (10) and plays a role of a memory function of maintaining the low light intensity state.
This phenomenon is also confirmed in Figs. 10 and 11.
Fig. 10a illustrates a relationship between light wavelength and - IT -~~~3W~
intensity which was detected by a photospectroanalyzer (1T) in the case where the current injected to the semiconductor laser device (1i) was increased from 54 mA to 99 mA at intervals of 3 mA. Fig. lOb represents the results of the detection by the photospectroanalyzer (1T) after transmission through the light transmitting medium (10). Fig. lla shows a relationship between light wavelength and intensity which was detected by a photospectroanalyzer (1T) in the case where the current injected to the semiconductor laser device (11) was decreased from 99 mA
to 54 mA at intervals of 3 mA. Fig. lib represents the results of the detection after transmission through the light transmitting medium (10).
It is understood in Fig. 10a that, as the injected current increases, light wavelength is discontinuously changed from T86.1 nm to T8T.5 nm at the injected current of T8 mA.
Fig. ila suggests that, as the injected current decreases, light wavelength is discontinuously changed from T8T.5 nm to T86.1 nm at 60 mA. From these Figs, 10a and 11a, it is confirmed that there is hysteresis against the injected current in changes of light wavelength. Figs. lob and 11b reveal that the laser beam of T8T.5 nm after transmitting through the light transmitting medium (10) is absorbed by the light transmitting medium (10).
In Figs. lOb and 11b, furthermore, comparison of the cases of the injected current of T5 mA demonstrates that, while a strong light intensity is observed in Fig. 10b, Fig. lib shows a light intensity of almost null.
'~93~~~
As shown in Fig. 9, therefore, when the controlled injected currents ?5 mA (low-carrier injection) and 99 mA (high-carrier injection) are entered in the semiconductor laser device (11), the light output (Fig. 9b) is irradiated into the light transmitting medium (10), and the resultant transmitting light is observed, it is confirmed that the light intensity output having a memory function as shown in Fig. 9c is obtained.
Because of the presence of hysteresis in the light wavelength change against the injected current, if light wavelength is changed by shifting from the low-carrier injection state to the high-carrier injection, light wavelength maintains the high-carrier injection state even after resuming to the low-carrier injection state. Thus, transmission of this laser beam through the light transmitting medium enables to achieve a memory function of holding the low-intensity state.
Fig. 12 shows a light absorption spectrum of the above-mentioned Er:YAG. In Fig. 12, the absorption peak is at ?8?.3 nm, and this corresponds with the excited absorption (2H11/2 4113/2) of Er3+ of Er:YAG.
EXA.MPhE 4 The laser head temperature was constantly kept at 43°C
using the same semiconductor laser device as in Example 3.
dscillated wavelengths of T8?.5 nm and T89.6 nm were respectively observed at the injected currents of ?5 mA and 99 mA. As is clear from the comparison of Figs. 13b and 13c, the light intensity plays a role of a memory which maintains the ~~93 ~~8 high light intensity state.
Figs. 14 and 15 illustrate the results of the measurement by the photospectroanalyzer (1?) of Fig. 8. Fig.
14a shows the results obtained by increasing the injected current from 54 mA to 99 mA at intervals of 3 mA, and Fig. 14b shows those obtained after transmission through the light transmitting medium (10). Fig. 15a, on the other hand, represents the results obtained by decreasing the injected current from 99 mA to 54 mA at intervals of 3 mA, and Fig. 15b represents the results obtained after transmission through the light transmitting medium (10).
Fig. 14a suggests that light wavelength discontinuously changes from T8T.5 nm to T89.6 nm at 81 mA. It is also understood from Fig. 15a that light wavelength discontinuously changes at 69 mA. These Figs. 14a and 15a suggests the presence of hysteresis in changes of light wavelength against the injected current. Figs. 14b and 15b demonstrate that the light having wavelength of T8T.5 nm is absorbed by the light transmitting medium (10), and the light of T89.6 nm transmitts through the medium.
As shown in Fig. 13a, therefore, when the controlling inputs for the injected currents at T5 mA (low-carrier injection) and 99 mA (high-carrier injection) are entered into the semiconductpr laser device (11), the light output (Fig. 13b) is irradiated into the light transmitting medium (10), and the transmitting light is observed, a memory function which maintains a high-intensity state of Fig. 13a is obtained.
- ao -'~t~~;~~~ , <<
As is clear from the results described in the above, a memory function of holding the respective state of a low light intensity and a high light intensity can be easily achieved by transmission of a light output through the Er:YAG light transmitting medium.
A of Fig. 16 shows an input waveform obtained in the case where oscillated wavelength was set so as to obtain about ?8?.5 nm for the infected current of 99 mA and a single-shaped pulse of 99 mA was formed. Relaxation oscillation inherent to a laser is observed. B of Fig. 16 represents a light waveform after transmission through the Er:YAQ light transmitting medium.
It should particularly be noted that the second and subsequent peaks of the relaxation oscillation are suppressed in B of Fig.
16. This means that, when oscillated wavelength reaches a constant wavelength, for example, ,~1 (?8?.5 nmj, in the initial build up, the light wavelength of ,~1 is maintained by hystereais effect even though the relaxation oscillation brings about a change of intensity, and that the light is absorbed after transmission through the light transmitting medium. Relaxation oscillation is suppressed, and a high-speed operation is available in the switching time of almost only a build up period. In this Example, the switching time was about 100 ps.
For a comparison, A and B of Fig. 1T respectively illustrates a single-shaped pulse input waveform at 99 mA
obtained by adjusting the laser head temperature and setting N
f~~y)e) light wavelength of T86 nm (not ,~1), and an output waveform after transmission through the light transmitting medium. It is confirmed from B of Fig. 1T that the input light of A transmitts through the medium with almost no absorption and is injured under relaxation oscillation effect.
In Examples in the above, Er3+ is used as a rare earth element to be doped in the light transmitting medium, but the present invention is not limited to this. Any appropriate material may be selected in accordance with light wavelength and the kind of the light transmitting medium. Any kind of light emitting device may be also appropriately employed.
OPTICAL DEVICE
FIELD OF THE INVENTION
The present invention relates to an optical device.
More particularly, the present invention relates to an optical controlling device useful fox a photo inverter and an optical functional device useful for an optical memory, both of which are indispensable for optical logical calculations and light computing in the photoelectronic field.
PRIOR ART
A photoelectronic technology has recently made a remarkable progress and is becoming a more important fundamental technology for an optical communication, an optical computer and the like.
Under these circumstances, an optical control method of performing logical culculations of a computer by means of optical signals has been studied as one of the control techniques for utilizing a light.
In the photoelectronics field including an optical communication and an optical information processing, for example, some researches are made on a control of a controlled light by a controlling light. According to this method, it is possible to achieve a switching operation higher in speed than that of an electrical switching circuit. It also permits multiple parallel processing operations by using an imaging ability of a light. The method is, therefore, considered to be N ~~ ~ ~ e! ti useful in the optical integrated circuit, for example.
An optical device using nonlinear optical effects is, on the other hand, studied for the purpose of an optical control.
While wavelength conversion effect such as a generation of a second higher harmonic has conventionally been considered to be important for the practical use, general attentions are now particularly directed toward an alteration of retractive index dependent on the light intensity and a change of absorption coefficient (Applied Physics, 59, 155-163 (February 1990)).
However, since these effects take place in a tertiary polarization, a nonlinear optical material having a higher-order polarization effect is required ["Degenerate fourwave mixing in semiconductor-doped glasses," J. Opt. Soc. Am., T3, 64?-653 (May 1983)]. Although an absorption-saturated type bistable semiconductor laser is considered to be most useful for a semiconductor optical control device, an optical input is employed for switchover from off-state to on-state, whereas a negative optical pulse does not exist for switchover from on-state to off-state (NOT circuit). Therefore, the bistable semiconductor laser has not been practically used (Applied Physics, 58, 15?4-1583 (November 1989)). The words "optical bistability" described herein means a phenomenon in which two stable states of output intensity are available for a single light intensity.
An optical memory is, on the other hand, becoming essential, which stares optical signal informations. The optical memory refers to a memory using a light when writing and reading informations, In a wide sense, however, it includes a memory using a light while either.
Although such optical memory is generally recognized to be important, only an analog imaging memory is currently utilized, and many others are still in the stage of research.
There are a holographic memory, a photomagnetic memory and a glass semiconductor memory which are considered to be more available among those. The holographic memory is a photograph of the optical interference given by a laser beam. This memory is, however, defective in that, while it allows a high-speed reading, it requires the writing and developing operations.
The photomagnetic memory is a memory which allows writing of informations by irradiating a laser beam to a ferromagnetic material such as MnBi arid reading of the informations by employing a Faraday effect in which polarization of a transmitting light is generated dependent upon the magnetization state. It is, however, defective in that light and magnetism are employed in parallel.
The glass semiconductor memory is a memory which permits writing and reading of informations by using a phenomenon in which the irradiation of a laser beam having an appropriate intensity to the glass semiconductor leads to a reversible phase transfer between polycrystalline and non-crystalline states, and transmittance is changed. Tt has, however, problems in that the switching speed of phase transfer is slow.
On the other hand, some researches have been performed in which an optical memory is designed by the bistable ~~~93 ~~8 semiconductor laser. This type of the memory, however, has not yet been practically attained because of similar problems mentioned in the above.
Generally, it is also known that a high-speed pulsation of the semiconductor laser produces relaxation oscillation in the intensity of the emitted light. This relaxation oscillation is observed in almost all kinds of laser, and the basic physical mechanism of this phenomenon is an interactive function between the electromagnetic field oscillated in the oscillator and the reversal distribution of atoms. An increase of the field intensity leads to a decrease of the reversal distribution density through an increase in induced emission factor. This, in turn, brings about a decrease in gain and then a decrease in the field intensity.
Although the semiconductor laser instantaneously rises up upon a fast-rising driving current, light intensity usually varies by about 1 nsec under the subsecquent relaxation oscillation until a certain value is reached. The pulse response speed is, therefore, limited to about 1 nsec on the maximum, and some studies are performed to control the relaxation oscillation.
An external light injection method is well-known in which a light is injected into a semiconductor laser conducting a direct modulation from another laser working in conjuction with the one. The external light injection suppresses relaxation oscillation (R. Lang and K. Kobayashi: Suppression of the relaxation oscillation in the modulated output of I
semiconductor lasers, IEEE J. Quantum Electron., QE-12, 3, 194-199 (1976)). xowever, this method is defective in that two lasers are needed and the oscillating axis modes ' thereof must be in correspondence with each Qther. ;
The present invention has an object to provide an optical device indispensable for carrying dut optical logical calculations and optical computing in the phatoalectronia field.
i More particularly, an object of the present invention is to provide an optical controlling device which aylows !
switching of an optical signal from on-state to off-i state, i.e., an optical SOT circuit, and permits full-optical logical calculations.
a Another object of the present invention is to provide an !
optical functional device which stores optical signal information through an electrical or optical input. , Therefore, in accordance with the present invention, there is provided an optical controlling device comprising a light transmitting medium showing a low transmittance far specific light wavelength ~i and a high transmittance for light wavelength ~Z around said i wavelength ~1, and a light emitting device emitting a light having light wavelength ~1 or ~~, wherein said !
optical controlling device controls light intensity in accordance with the emitted light having wavelength ~1 or ~2 thrbugh irradiation from said light emitting device and transmission of the emitted light through said light transmiting medium.
S
Also in accordance with the present invention, there is provided an optical controlling device comprising a light .
transmitting medium showing a low transmittanGe ~or specific light wavelength ~1 and a high txansmittance for light wavelength ~z around said wavelength ~l, and a light , emitting device emitting a light having wavelength ~1 or ~z, wherein said optical controlling device controls light intensity in accordance with the emitted light having wavelength ~1 or ~2 through irradiation from said light .
emitting device and transmission of the emitted light ;
through said licht transmitting medium, wheroin said light emitting device is a semiconductor laser, said semiconductor laser respectively emitting wavelengths ~Z and ~~ at a low- , current and a high-current in5ections, or respectively emitting wavelengths ~l and ~2 at a low- ;
current and a high-current injections. , Further in accordance with the present invention, there is provided an optical controlling device comprising a ' light transmitting medium showing a low transmittance for specific light wavelength ~1 and a high transmittance for light wavelength ~2 around said wavelength ~~, and a light , emitting device emitting a light having wavelength ~~ or i ~2, wherein said optical controlling device controls light , intensity in accordance with the emitted light having wavelength ~1 yr ~2 through irradiation from said light emitting device and transmission of the emitted light through said light transmitting medium, wherein said light transmitting medium comprises a substance selected from the group consisting of , transparent ceramics, a glass, a semiconductor and 5a an insulator, said substance having added thereto at least one rare earth element, wherein said at least one rare earth element is erbium, Er3+
, wherein said light wavelength 7~1 for which said light transmitting medium k~as a low transmittance is near an excited absorption peak (zHll~2-4I13,z) of erbium, Erg' . i Still further in accordance with the present inven,ti.vr~, there is provided an optical controlling device , comprising a light transmitting medium showing a low transmittance for specific light wavelength ~,1 and a high transmittanoe for light wavelength ~,2 arouxzd sa:Ld , wavelength 7~1, and a light emitting device emitting a , light having wavelength 7~1 or ~,Z, wherein said optical controlling device controls light intensity in accordance with the emitted light having wavelength ~,1 or 7~2 through , irradiation from said light emitting device and transmission of the emitted light through said light transmitting medium, ' wherein said light transmitting medium comprises a substance selected from the group oonsisting of transparent ceramics, a glass, a semiconductor and an insulator, sand substance havixlg added thereto at least one rare earth element, i wherein said at least one rare earth element is erbium, ~x3+ .
wherein said light transmitting medium is composed of transparent ceramics of YAG (yttrium-aluminum-garnet) with added erbium, Er3', wherein said light wavelength 7~1 for which said light , transmitting medium has a low transmittance is near 5b an excited absorption peak ~2Isa11/2-a~.13/1~ of erbium, Er3+. , Still further in accordaz~oe with the present invention, .
there is prow ded an optical functional device comprising a light transmittixzg medium showing a low tr&nSmittaYiCe for specific light wavelength ~t,l aY~d high transmittance , for' light wavelengths ~.2 and ~.g around said wavelength a,1 (~z ~~1 ~~3 ) , and a light emitting device changing wavelength while accompanying a generation of hysteres~.s dependent upon the quantity of cuxxent injection or light .
irradiation, and emitting a light having light wavelength i ~1. ~.2 or ~3 wherein a light of wavelength ~,1, J~z or ~3 is ~xrad~.a.ted from $aid light emitting device to said light transmitting medium, the intensity o~ said light transmitting through said light transmitting medium is , maintained at a low or high state under the effect of said hysteresis, thereby a memory function is obtainad.
This and other objects, features and advantages of the invention will beCOrne more aLbparent upon reading of thA
following detailed specification and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an embodiment of ;
the optical controlling device and the device for measuring its functions; , FIGS. 2a, 2b and 2c are respectively correlation diagrams illustrating the electric cuxrent injected to a i semiconductor laser cle~erice., the light intensity of the output light of the semiconductor laser device, and the optioal , 5c ~~~~~o intensity after transmission through a light transmitting medium;
Fig. 3 is a correlation diagram between the injected current to the semiconductor laser device and the light transmittance;
Fig. 4 is a correlation diagram between the injected current to the semiconductor laser device and the light intensity;
Fig. 5 is a diagram of the light absorption spectrum of the light transmitting medium;
Fig. 6 is a block diagram illustrating another embodiment of the optical controlling device and the device for measuring its functions;
Fig. 7 is a correlation diagram between the laser intensity and the transmittance;
Fig. a is a block diagram illustrating an embodiment of the optical functional device and the device for measuring its functions;
Figs. 9a, 9b and 9c are respectively correlation diagrams illustrating the injected current to a semiconductor laser device, the light intensity of the output light and the light intensity after transmission through a light transmitting medium;
Figs. 10a and lOb are respectively correlation diagrams between light wavelength and intensity when increasing the injected current;
Figs. 11a and 11b are respectively correlation diagrams ~?i)~3 ~~8 between light wavelength and intensity when decreasing the injected current;
Fig. 12 is a diagrm of the light absorption spectrum of the light transmitting medium;
Figs. 13a, 13b and 13c are respectively correlation diagrams illustrating the injected current to the semiconductor laser device, the light intensity of the output light, and the light intensity after transmission through the light transmitting medium;
Figs. 14a and 14b are respectively correlation diagrams between light wavelength and intensity when increasing the injected current, respectively;
Figs. 15a and 15b are respectively correlation diagrams between light wavelength and intensity when decreasing the injected current;
Fig. 16 illustrates output waveforms of single-shaped pulses; and Fig. 1T illustrates another output waveforms of single-shaped pulses.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an optical controlling device which comprises a light transmitting medium showing a low transmittance for specific light wavelength ~1 and a high transmittance far light wavelength ,~2 around said wavelength ,~1, and a light emitting device emitting a light having light - T -~~~3a~~
wavelength ,~1 or ,~2, wherein said optical controlling device controlls light intensity in accordance with changes in a controlled light through light irradiation of said controlled light having wavelength ,~1 or ,~2 from said light emitting device and light transmission of the controlled light through said light transmitting medium.
A light emitting device of the optical controlling device emits a light of either light wavelength ,~1 or ,~2 by applying an external electrical or optical controlling input.
The transmittance of a light transmitting medium is controlled by means of the controlled light.
In the present invention, light properties of the light transmitting medium are controlled for accomplishing the light control, and a specific element including, for example, a rare earth element is added to an appropriate material such as transparent ceramics, a glass, a semiconductor or an insulator.
A rare earth element optically shows the inner shell transition so that it is hardly affected by the base material. By adding this rare earth element as a doping element to the light transmitting medium, it is possible to generate a ground absorption from the ground level E1 to the excited level E3 and an excited absorption from the metastable level E2 to the excited levEl E4 for the light of ,~l (E4 > EZ > E3 > E1)' Therefore, the transmittance at light wavelength ,~1 is considerably reduced.
On the other hand, when a controlling input is electrically or optically entered in the light emitting device, _ g _ N~~JO~d the emitted wavelength varies from ,~1 to ,~2, or from ,~2 to ,~1, For example, it is generally known that, when using a semiconductor laser as a light emitting device, the emitted wavelength discontinuously varies toward longer wavelength, as the quantity of the injected current increases (M. Nakamura, "Single mode operation of semiconductor injection lasers," IEEE
Trons. Circuits and Systems, CAS-26, 1055 (19T9)j. If oscillated wavelength varies from ,~2 to ,~1 when the injected current to the semiconductor laser is increased, the light intensity of ,~1 becomes bigger than that of a2 because of the larger quantity of the injection. However, when the output of the semiconductor laser is irradiated to the above-mentioned light transmitting medium, light output of ,~1 becomes smaller than that of ,~2 because the transmittance of light wavelength ,~1 is lower than that of ,~2, thus achieving an optical NOT circuit.
In the present invention, since the light transmitting medium exhibits a low transmittance for light wavelength ,~1 and a high transmittance for ,~2, respectively, a light having light wavelength ,~1 is absorbed when the light is entered in the light transmitting medium, thus the off-state being achieved. The on-state is given by transmission of a light having light wavelength ,~2 when the light is entered. Further, since it is possible to dope an element which generates the excited absorption for the light of wavelength ,~1, the excited absorption which has a higher degree of absorption than the ground absorption takes place, and as a result, the -N(~~3W~
transmittance of ,~1 transmitting through the light transmitting medium is considerably reduced according to the excited absorption. The difference of the transmittance between the light of ~1 and the one of ,~2 each of which transmits through the light transmitting medium becomes remarkable, thus enabling to obtain an optical inverter (NOT circuit) having a large ratio ON/OFF. Combining a plurality of the optical inverters enables to make up any logical circuit (NOR, XOR, for example). It is thus possible to achieve optical logical calculations and optical computers by using the optical controlling device of the present invention as a key device.
The present invention also provides an optical functional device which comprises a light transmitting medium showing a low transmittance for specific light wavelength ,~1 and a high transmittance for light wavelengths ,~2 and ,~3 around said wavelength ,~1 (,~~ < ,~1 < ,~3), and a light emitting device changing wavelength while accompanying a generation of hysteresis dependent upon the quantity of current injection or light irradiation, and emitting a light having light wavelength ~1' ~2 °r ~3~ wherein a light of wavelength ,~1, ,~2 or ,~3 is irradiated from said light emitting device to said light transmitting medium, the intensity of said light transmitting through said light transmitting medium is maintained at a low or high state under the effect of said hysteresis, thereby a memory function is obtained.
A light emitting device in this optical functional - l0 -~'f~~3u3~
device emits a controlled light of either light wavelength ,~1, or ,~3 though entering an electrical or optical controlling input. The transmittance of the light transmitting medium is controlled by the controlled light and the intensity of the light transmitting through the light transmitting medium is maintained at a low or high state because the change of wavelength has hysteresis against the controlling input. And then, a memory function is realized.
In the present invention, optical properties of the light transmitting medium are controlled as in the case of the above-mentioned optical controlling device, and a specific element such as a rare earth element is added to an appropriate material such as transparent ceramics, a glass, a semiconductor or an insulator. Consequently, the light transmitting medium exhibits a low transmittance for light wavelength ~1 and a high transmittance for light wavelengths ,~2 and ,~3. When a light of wavelength ,~1 is entered into this light transmitting medium, the light is absorbed to give the off-state, and the entry of a light of wavelength ,~2 or ,~3 realizes the on-state through the transmission of the light. Further, since wavelength change from ,~2 to ~1 , or from ,~1 to ,~3 has hysteresis against the controlling input, the off-state and the on-state are maintained.
On the other hand, when the controlling input is electrically or optically entered in the light emitting device, the emitted wavelength varies from ,~2 to ,~1, or from ,~1 to It is generally known that, when a semiconductor laser is used ~'i1~3 ~3 as a light emitting device, decrease of the amount of the current injection from the large quantity state produces a discontinuous change in the oscillated wavelength toward short wavelength side while accompanying hysteresis (M. Nakamura, "Single mode operation of semiconductor injection lasers," IEEE
Trons. Circuits and Systems, CAS-26, 1055 (19?9)). When a current is increased from a low injection state to a high state in that semiconductor laser, oscillated wavelength is changed from ~2 to ,~1, and then the low injection state is resumed, the oscillated wavelength ,~1 is maintained and the low transmittance state (i.e., off-state) is also maintained even at the recovered low injection state. This is because the oscillated wavelength has hysteresis against the injected current. Similarly, when oscillated wavelengths ~1 and ,~3 are respectively produced at the low and high injection states, the oscillated wavelength ,~
is maintained and the high transmittance state (i.e., on-state) is also maintained even at the returned low injection. This permits achievement of a memory function.
Hy using this memory function, it is possible to eliminate the harm of relaxation oscillation which is one of the causes to deteriorate the pulse-driven switching speed of a semiconductor laser, thus permitting a high-speed switching operation. For example, when the current of a semiconductor laser is changed from null or a low injection state to a high injection state to produce oscillated wavelength ~1, the oscillated wavelength of ,~1 is maintained under the hysteresis effect even upon a slight change in the quantity of the injected ~U5'3 i~~
current (relaxation oscillation). Even if relaxation oscillation takes place in terms of the light intensity, therefore, the change in the intensity accompanied by the relaxation oscillation can be eliminated by transmitting through the above-mentioned light transmitting medium. The switching time of the optical functional device is limitted by only the rising time of the semiconductor laser, thus permitting achievement of a high-speed switching operation.
The optical functional device may be arranged in a resonator of a semiconductor laser beam emitting device, for example. In this case, the laser beam is repeatedly reflected in the resonator and is absorbed by the light transmitting medium every reflection. This enables to lengthen an effective length of the light transmitting medium and to be made up the light transmitting medium of a thin film, thus permitting downsizing of the optical functional device. In the optical functional device, furthermore, a multistage connection is possible. A conceivable method for this multistage connection would be proposed in which a light-receiving device such as a phototransistor or a photodiode is connected to the optical functional device. The light-receiving device would receive a light signal from the preceding stage, so that the output current therefrom can be used for the injection current for the light emitting device and the multistage connection is realized.
The optical functional device makes it possible to achieve an optical memory. The optical memory enables to make up any of the switch-off type (low light intensity state) and ~~~35~$
the switch-on type (high light intensity state) relative to the controlling input by selecting light wavelength. When switching the optical functional device, there is no harm of relaxation oscillation, permitting a high-speed operation.
The optical controlling and functional devices of the present invention may be referred to Optical logic devices by red-shift of diode laser and inverter of optical nonlinear absorption: ORION.
In Fig. 1, a rod having a size of ~ 3 mm x 3 mm composed of yttrium-aluminium-garnet (YAG) added erbium (Er3*) therein was employed as a light transmitting medium (10). The Er concentration was 50 at.%.
A semiconductor laser device (11) as a light emitting device was driven by a drive control circuit (12) and a temperature adjuster (13j to generate a laser beam having a constant wavelength, which was irradiated into the light transmitting medium (10) composed of the Er:YAG through a beam splitter (14) and a condenser lens (15).
The light output through the light transmitting medium (10) was received by a light detecting device (16) and was observed by means of a digital oscilloscope (1T) and a light power meter (18). The results are shown in Figs. 2 and 3.
Comparison of Figs. 2b and 2c reveals that the values of light intensity B and C of the output from the semiconductor laser device (11j which are shown in Fig. 2b were reversed, as ~i#q3~ ~~
shown in Fig. 2c, after transmitting through the light transmitting medium (10). This phenomenon can be also confirmed in Fig. 3. At the point D of Fig. 3, the transmittance considerably decreases to about a third.
Using a spectroscope (19) shown in Fig. 1, changes of wavelength of the laser output relative to the injected current of the semiconductor laser device (11) were measured. The results are shown in Fig. 4. In Fig. 4, black circles represent values of light detection intensity when wavelength of the spectroscope (19) was set at T8T nm, and the white circles repreaent those observed when wavelength was set at T84.5 nm.
At the paint E (T3 mA) in Fig. 4, the light intensity of T84.5 nm sharply decreases while the light intensity of TeT nm considerably increases. This suggests that, as a result of increase of the injected current to the semiconductor laser device (11), the center oscillated wavelength discontinuously changed at the point E from T84.5 nm to T8T nm. The value of the infected current at this discontinuous point E corresponds with the value of in3ected current at the point D of Fig. 3. As is clear from Fig. 5, furthermore, the absorption peak for the light transmitting medium (10) was at T8T nm, this corresponding with the excited absorption (2E11/2 4113/2) °g Er3* in Er:YAG.
As is evident from the results as described above, the phenomenon shown in Fig. 2, in which the light output is reversed by transmission through the Er:YAG light transmitting medium (10), is easily understood.
~'~~3W8 In Fig. 6, a i~~ 3 mm x 25 mm Er:YAG rod was employed as a light transmitting medium (10), having an Er concentration of 16 at . 9b .
A semiconductor laser device (11) as a light emitting device was driven by a drive control circuit (12) to produce.a laser beam of a center wavelength of T87 nm, which was irradiated into the Er:YAG light transmitting medium (10) through a beam splitter (14) and a condenser lens (15). This laser beam was received by a light detecting device (10j, and the light intensity was measured by an optical power meter (18) to calculate the transmittance. The results are shown in Fig.
T.
The in3ected current to the semiconductor laser device (11) was constantly set at 99 mA, and the laser beam intensity was varied through an automatic rotary ND (neutral density) filter (20).
Fig. ~ demonstrates that the value of transmittance at the point B is about twice as high as those at the points A and C. It is thus confirmed that the change of the laser beam intensity from at the point A to at the point B brings about a high transmittance state (light switch-on), and the one from at the point B to at the point C brings about a low transmittance state (light switch-off).
It is also confirmed that the effect in which the tranamittance dicreases (from the point B to the point C) against the increase of the light intensity improves the on/off ~?i~~3~~~
ratio of the inverter shown in 8xample 1.
a~ "..,.,t ., ,.
In Fig. 8, a rod having a size of ~ 3 mm x 3 mm composed of yttrium-aluminium-garnet (YAG) doped erbium (Er3~) was employed as a light transmitting medium (10). A concentration of Er was set at 50 at.%, i.e., a composition of (Er0.5Y0.5)3A15~12' A semiconductor laser device (11) as a light emitting device was driven by a drive control circuit (i2) and a temperature adjuster (13) to generate a laser beam of a constant wavelength, which was irradiated into the light transmitting medium (10) of Er:YAG through a beam slitter (14).
The output light transmitting through the light transmitting medium (10) was received by a light detecting device (15) and was observed by means of a digital oscilloscope (10) and an optical spectroanalyzer (1~). The laser head was heated and constantly kept at 33°C by the temperature adjuster (13). The results are shown in Fig. 9.
Comparison of Figa. 9b and 9c reveals that a change of the light intensity of the output from the semiconductor laser device (11) of Fig. 9b is reversed (a low light intensity state) after transmitting through the light transmitting medium (10) and plays a role of a memory function of maintaining the low light intensity state.
This phenomenon is also confirmed in Figs. 10 and 11.
Fig. 10a illustrates a relationship between light wavelength and - IT -~~~3W~
intensity which was detected by a photospectroanalyzer (1T) in the case where the current injected to the semiconductor laser device (1i) was increased from 54 mA to 99 mA at intervals of 3 mA. Fig. lOb represents the results of the detection by the photospectroanalyzer (1T) after transmission through the light transmitting medium (10). Fig. lla shows a relationship between light wavelength and intensity which was detected by a photospectroanalyzer (1T) in the case where the current injected to the semiconductor laser device (11) was decreased from 99 mA
to 54 mA at intervals of 3 mA. Fig. lib represents the results of the detection after transmission through the light transmitting medium (10).
It is understood in Fig. 10a that, as the injected current increases, light wavelength is discontinuously changed from T86.1 nm to T8T.5 nm at the injected current of T8 mA.
Fig. ila suggests that, as the injected current decreases, light wavelength is discontinuously changed from T8T.5 nm to T86.1 nm at 60 mA. From these Figs, 10a and 11a, it is confirmed that there is hysteresis against the injected current in changes of light wavelength. Figs. lob and 11b reveal that the laser beam of T8T.5 nm after transmitting through the light transmitting medium (10) is absorbed by the light transmitting medium (10).
In Figs. lOb and 11b, furthermore, comparison of the cases of the injected current of T5 mA demonstrates that, while a strong light intensity is observed in Fig. 10b, Fig. lib shows a light intensity of almost null.
'~93~~~
As shown in Fig. 9, therefore, when the controlled injected currents ?5 mA (low-carrier injection) and 99 mA (high-carrier injection) are entered in the semiconductor laser device (11), the light output (Fig. 9b) is irradiated into the light transmitting medium (10), and the resultant transmitting light is observed, it is confirmed that the light intensity output having a memory function as shown in Fig. 9c is obtained.
Because of the presence of hysteresis in the light wavelength change against the injected current, if light wavelength is changed by shifting from the low-carrier injection state to the high-carrier injection, light wavelength maintains the high-carrier injection state even after resuming to the low-carrier injection state. Thus, transmission of this laser beam through the light transmitting medium enables to achieve a memory function of holding the low-intensity state.
Fig. 12 shows a light absorption spectrum of the above-mentioned Er:YAG. In Fig. 12, the absorption peak is at ?8?.3 nm, and this corresponds with the excited absorption (2H11/2 4113/2) of Er3+ of Er:YAG.
EXA.MPhE 4 The laser head temperature was constantly kept at 43°C
using the same semiconductor laser device as in Example 3.
dscillated wavelengths of T8?.5 nm and T89.6 nm were respectively observed at the injected currents of ?5 mA and 99 mA. As is clear from the comparison of Figs. 13b and 13c, the light intensity plays a role of a memory which maintains the ~~93 ~~8 high light intensity state.
Figs. 14 and 15 illustrate the results of the measurement by the photospectroanalyzer (1?) of Fig. 8. Fig.
14a shows the results obtained by increasing the injected current from 54 mA to 99 mA at intervals of 3 mA, and Fig. 14b shows those obtained after transmission through the light transmitting medium (10). Fig. 15a, on the other hand, represents the results obtained by decreasing the injected current from 99 mA to 54 mA at intervals of 3 mA, and Fig. 15b represents the results obtained after transmission through the light transmitting medium (10).
Fig. 14a suggests that light wavelength discontinuously changes from T8T.5 nm to T89.6 nm at 81 mA. It is also understood from Fig. 15a that light wavelength discontinuously changes at 69 mA. These Figs. 14a and 15a suggests the presence of hysteresis in changes of light wavelength against the injected current. Figs. 14b and 15b demonstrate that the light having wavelength of T8T.5 nm is absorbed by the light transmitting medium (10), and the light of T89.6 nm transmitts through the medium.
As shown in Fig. 13a, therefore, when the controlling inputs for the injected currents at T5 mA (low-carrier injection) and 99 mA (high-carrier injection) are entered into the semiconductpr laser device (11), the light output (Fig. 13b) is irradiated into the light transmitting medium (10), and the transmitting light is observed, a memory function which maintains a high-intensity state of Fig. 13a is obtained.
- ao -'~t~~;~~~ , <<
As is clear from the results described in the above, a memory function of holding the respective state of a low light intensity and a high light intensity can be easily achieved by transmission of a light output through the Er:YAG light transmitting medium.
A of Fig. 16 shows an input waveform obtained in the case where oscillated wavelength was set so as to obtain about ?8?.5 nm for the infected current of 99 mA and a single-shaped pulse of 99 mA was formed. Relaxation oscillation inherent to a laser is observed. B of Fig. 16 represents a light waveform after transmission through the Er:YAQ light transmitting medium.
It should particularly be noted that the second and subsequent peaks of the relaxation oscillation are suppressed in B of Fig.
16. This means that, when oscillated wavelength reaches a constant wavelength, for example, ,~1 (?8?.5 nmj, in the initial build up, the light wavelength of ,~1 is maintained by hystereais effect even though the relaxation oscillation brings about a change of intensity, and that the light is absorbed after transmission through the light transmitting medium. Relaxation oscillation is suppressed, and a high-speed operation is available in the switching time of almost only a build up period. In this Example, the switching time was about 100 ps.
For a comparison, A and B of Fig. 1T respectively illustrates a single-shaped pulse input waveform at 99 mA
obtained by adjusting the laser head temperature and setting N
f~~y)e) light wavelength of T86 nm (not ,~1), and an output waveform after transmission through the light transmitting medium. It is confirmed from B of Fig. 1T that the input light of A transmitts through the medium with almost no absorption and is injured under relaxation oscillation effect.
In Examples in the above, Er3+ is used as a rare earth element to be doped in the light transmitting medium, but the present invention is not limited to this. Any appropriate material may be selected in accordance with light wavelength and the kind of the light transmitting medium. Any kind of light emitting device may be also appropriately employed.
Claims (22)
1. An optical controlling device comprising a light transmitting medium showing a low transmittance for specific light wavelength .lambda.1 and a high transmittance for light wavelength .lambda.2 around said wavelength .lambda.1, and a light emitting device emitting a light having light wavelength .lambda.1 or .lambda.2, wherein said optical controlling device controls light intensity in accordance with the emitted light having wavelength .lambda.1 or .lambda.2 through irradiation from said light emitting device and transmission of the emitted light through said light transmiting medium.
2. A controlling device as claimed in Claim 1, wherein said light transmitting.medium comprises a substance selected from the group consisting of transparent ceramics, a glass, a semiconductor and an insulator, said substance having added thereto at least one rare earth element.
3. A controlling device as claimed in Claim 2, wherein said at least one rare earth element is erbium, Er3+.
4. A controlling device as claimed in Claim 3, wherein said light transmitting medium is composed of transparent ceramics of YAG (yttrium-luminium-garnet) with added erbium, Er3+.
5. A controlling device as claimed in Claim 3, wherein said light wavelength .lambda.1 for which said light transmitting medium has a low transmittance is near an excited absorption peak (2H11/2-4I13/2) of erbium,Er3+.
6. A controlling device as claimed in Claim 4 wherein said light wavelength .lambda.1 for which said light transmitting medium has a low transmittance is near an excited absorption peak (ZH11/2-4I13/2) of erbium, Er3+.
7. A controlling device as claimed in Claim 1, wherein said light emitting device is a semiconductor laser, said semiconductor laser respectively emitting lights of light wavelengths .lambda.2 and .lambda.1 at a low-current and a high-current injections, or respectively emitting lights of wavelengths .lambda.1 and .lambda.2 at a low-current and a hight-current injections.
8. A controlling device as claimed in Claim 7, wherein said light emitting device as an absorption-saturated type semiconductor laser.
9. An optical functional device comprising a light transmitting medium showing a low transmittance for specific light wavelength .lambda.1 and high transmittance for light wavelengths .lambda.2 and .lambda.3 around said wavelength .lambda.1 (.lambda.2 <.lambda.1 <.lambda.3), and a light emitting device changing wavelength while accompanying a generation of hysteresis dependent upon the quantity of current injection or light irradiation, and emitting a light having light wavelength .lambda.1, .lambda.2 or .lambda.3 wherein a light of wavelength .lambda.1, .lambda.2 or .lambda.3 is irradiated from said light emitting device to said light transmitting medium, the intensity of said light transmitting through said light transmitting medium is maintained at a low or high state under the effect of said hysteresis, thereby a memory function is obtained.
10. A functional device as claimed in claim 9, wherein said light emitting device is a semiconductor laser which permits carrier injection to an excited area by means of a current or a light, changes a light wavelength from .lambda.2 to .lambda.1 when shifting from a low-carrier injection to a high-carrier injection, maintains said light wavelength of .lambda.1 by hysteresis when said low-carrier injection is resumed, and keeps a light intensity transmitting through said light transmitting medium at a low-intensity state, said semiconductor laser further changing light wavelength from .lambda.1 to .lambda.3 when shifting from a low-carrier injection to a high-carrier injection, maintains said light wavelength of .lambda.3 by hysteresis when said low-carrier injection is resumed, and keeping a light intensity transmitting through said light transmitting medium at a high-intensity state.
11. A functional.device as claimed in claim 10, wherein said light transmitting medium comprises a substance selected from the group consisting of transparent ceramics, a glass, a semiconductor and an insulator, said substance being added with at least one rare earth element.
12. A functional device as claimed in claim 11, wherein said at least one rare earth element is erbium, Er3+.
13. A functional device as claimed in claim 12, wherein said light transmitting medium is composed of transparent ceramics of YAG (yttrium-aluminium-garnet) with added erbium, Er3+.
14. A functional device as claimed in. claim 13, wherein said light wavelength .lambda.1 for which said light transmitting medium has a low transmittance is near an excited absorption peak (2H11/2-4I13/2) of erbium Er3+.
15. A functional device as claimed in claim 12, wherein said light wavelength .lambda.1 for which said light transmitting medium has a low transmittance is near an excited absorption peak (2H11/2-4I13/2) of erbium Er3+.
16. A functional device as claimed in claim 9, wherein said light transmitting medium comprises a substance selected from the group consisting of transparent ceramics, a glass, a semiconductor and an insulator, said substance being added with at least one rare earth element.
17. A functional device as claimed in claim 16, wherein said at least one rare earth element, is erbium, Er3+.
18. A functional device as claimed in claim 17, wherein said light transmitting medium is composed of transparent ceramics of YAG(yttrium-aluminum-garnet) with added erbium, Er3+.
19. A functional device as claimed in claim 18, wherein said light wavelength .lambda.1 for which said light transmitting medium has a low transmittance is near an excited absorption peak (2H11/2-I13/2) of erbium Er3+.
20. A functional device as claimed in claim 17, wherein said light wavelength .lambda.1 for which said light transmitting medium has a low transmittance is near and excited absorption peak (2H11/2-4I13/2) of erbium Er3+.
21. A functional device as claimed in claim 9, wherein said functional device suppresses variations of a light intensity caused by relaxation oscillation during a laser oscillation.
22. A functional device as claimed in claim 9, wherein said light transmitting medium is provided in a resonator of a semiconductor laser beam emitting device, and a light-receiving device is connected, thereby said functional device is downsized and has a multistage connection structure.
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP15536892A JP3224858B2 (en) | 1992-06-15 | 1992-06-15 | Light control element |
| JP155368/1992 | 1992-06-15 | ||
| JP4341035A JPH05247036A (en) | 1991-12-03 | 1992-11-30 | Thiazolyl-substituted quinolylmethoxyphenylacetic acid derivative |
| JP321035/1992 | 1992-11-30 | ||
| US08/043,791 US5406420A (en) | 1992-06-15 | 1993-04-07 | Optical device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2093538A1 CA2093538A1 (en) | 1993-12-16 |
| CA2093538C true CA2093538C (en) | 2006-05-09 |
Family
ID=27320824
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002093538A Expired - Fee Related CA2093538C (en) | 1992-06-15 | 1993-04-06 | Optical device |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2093538C (en) |
-
1993
- 1993-04-06 CA CA002093538A patent/CA2093538C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2093538A1 (en) | 1993-12-16 |
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