JPH07122803A - Ring laser - Google Patents

Abstract

PURPOSE:To enable reduction of an operation time, shrotening of a length of an entire of a ring resonator, increase of freedom of selection of an oscillation wavelength, etc., by constituting an optical amplification element of a traveling waveform semiconductor laser optical amplification element. CONSTITUTION:An optical amplification element 1, a wavelength selection means 2, a first optical branching means 3 which outputs circulating light to an outside and an isolator 6 are connected to a ring shape to form a resonator. In such a ring laser, the optical amplification element 1 is constituted of a traveling waveform semiconductor laser optical amplification element, and a saturable absorber 5 wherein translucent coefficient changes according to light input is provided. Furthermore, a second optical branching means 4 for introducing light from an outside to at least one of an input end and an output end of the optical amplification element 1 is provided to increase strength of output of a first optical branching means 3 when first light pulse is introduced and to reduce strength of output of the first optical branching means 3 when second light pulse which is behind first light pulse is introduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ring laser used for logical operation using light and information processing.

[0002]

2. Description of the Related Art In an optical logic circuit which performs logical operation by correlating the intensity of optical power in an optical circuit with "1" and "0" of information processing, an optical storage element controlled by light is an important constituent element. one of. As an example of such an optical storage element, a laser using a rare earth element-doped optical fiber as an optical amplification element is disclosed in Japanese Patent Application Laid-Open No. 5-100277, "Optical storage device and optical logic device". FIG. 6 shows an example of the configuration of a laser device which is an optical storage device. In this laser device, an optical amplifying element A made of a rare earth element-doped optical fiber, an isolator I, a wavelength selecting filter J, an input light and output light optical coupler C, and an excitation coupler Ce are coupled by an optical fiber, and the whole is connected. A ring resonator, which will be the resonator as
That is, a ring laser is formed. Where EIN
When a predetermined pumping light is given from a pumping light source (not shown) connected to the optical amplifier via the pumping coupler Ce, the optical amplifying element A is set to exhibit an abnormal amplifying characteristic. The operation is realized.

The abnormal amplification characteristic will be described below.
FIG. 7 shows the input light power-gain characteristics of the optical amplifier element A, in which the horizontal axis represents the input signal light power and the vertical axis represents the gain. The broken line shows the amplification characteristic of an optical amplification element using a semiconductor laser or a usual rare earth element-doped optical fiber amplification element, and the solid line shows the amplification characteristic of an abnormal amplification element. An optical amplification element using a semiconductor laser or an ordinary rare earth element-doped optical fiber amplification element has a characteristic that the gain changes substantially at a low level of input signal light power and decreases at a high level. (Dashed line). On the other hand, the abnormal amplification element is characterized by having a region (Pso to Psth) having a positive correlation between the input signal light power and the gain (solid line). In the above-mentioned prior art, in the rare earth element-doped optical fiber amplifying element, the abnormal amplification characteristics include the product of the concentration of the rare earth element of the fiber and the fiber length (hereinafter, abbreviated as concentration length product) and the pumping light power. It has been shown to be obtained when in range. In this laser device, the output when not oscillating is set to "0", and the output when oscillating when the gain of the abnormal amplification element exceeds the loss of the entire ring resonator is set to "0".
1 ”state. In FIG. 7, the gain at the time of oscillation is defined as an oscillation threshold value, Gsth.
When input light of a level corresponding to 0 "is incident, the gain of the abnormal amplification element is lower than Gsth and is in Go.
The pumping light is given so that it becomes Gsth when there is input light at a level corresponding to 1 ″.

The operation of the laser will be described below with reference to FIG. In FIG. 8, the horizontal axis represents the input signal light power and the vertical axis represents the output signal light power. (1) First, the input light level is "0" in the initial state.
When, the gain of the abnormal amplification element is low and is less than the loss of the entire ring resonator, so that oscillation does not start. That is, it is a "0" state. (Point A in FIG. 8) (2) Next, when "1" level light is input, the gain increases due to this optical power, and when Gsth shown in FIG. 7 is reached, the abnormal amplification element starts oscillation. . That is, "1"
The state is set (point B in FIG. 8). The oscillation wavelength is determined by the transmission wavelength of the wavelength selection filter J. (3) Once the laser device starts to oscillate, this oscillation output is fed back to the input terminal of the abnormal amplification element, so that the gain of the abnormal amplification element is fixed as it is and the level of the input light is "0". Oscillation continues even after returning to the state. That is, it means that the "1" state is stored. (Fig. 8
(Point C) (4) Here, in order to reset the laser to the original "0" state, an optical switch or the like is provided to cut off the ring resonator, or the pumping light source is controlled to cut off the pumping light once. In some cases (neither is shown), oscillation is stopped and the state is returned to "0". (Point A in FIG. 8) As described above, in the conventional technique, the binary state is maintained by utilizing the characteristics of the abnormal amplification element. Further, according to this operation principle, the time (hereinafter, abbreviated as operation time; refer to FIG. 5) until the light to be set to the “1” state is input and oscillates is the time for the input light to make a round in the ring resonator, It can be seen that the gain in the extraordinary optical amplifier is the sum of the time required to follow the change in the input light level.

[0005]

However, the laser device which is the conventional optical storage device shown in FIG. 6 has a problem that the operating time is long. This is because it is difficult to make the length of the rare earth element-doped optical fiber used for the abnormal amplification element extremely short, and therefore the time for one round of the ring resonator cannot be shortened. This is because, as disclosed in the above-mentioned application, in order to obtain the abnormal amplification characteristic, the concentration product of the rare earth element-doped optical fiber is about 20,000 pp.
It is necessary to set as high as m · m or higher. In this way, when the concentration product is determined, it is necessary to increase the concentration to shorten the fiber length.
As shown in Vol.84, pp.41-48 “Er-doped fiber amplifier”, when the concentration is increased, the concentration quenching phenomenon causes a decrease in gain, which has a certain limit. Therefore, the fiber length actually used for the ring resonator is at least several meters.

[0006]

Therefore, the present invention adopts the following configuration. First, as the optical amplification element 1, a traveling waveform semiconductor laser optical amplification element was adopted. The traveling-waveform semiconductor laser light amplification element is an element having an input / output terminal for inputting / outputting as well as suppressing laser oscillation by providing a non-reflective film on a resonator surface for oscillating laser of a semiconductor laser. Since this traveling waveform semiconductor laser light amplification element (hereinafter referred to as semiconductor laser light amplification element) does not have abnormal amplification characteristics, optical storage was realized by combining the saturable absorber 5 with a ring laser. In addition, the second light branching means 4 for inputting light from the outside into the semiconductor laser light amplification element
It was adopted. That is, the optical amplification element 1, the wavelength selection means 2, and the first optical branching means 3 for outputting the circulating light to the outside.
In a conventional ring laser in which the resonator and the isolator 6 are connected in a ring shape to form a resonator, the optical amplification element 1 is composed of a semiconductor laser optical amplification element, and the optical transmission coefficient changes depending on the input light. Saturable absorber 5
When the first optical pulse is introduced, the intensity of the output from the first optical branching means 3 is increased, and when the second optical pulse delayed from the first optical pulse is introduced, the first optical pulse is introduced.
In order to reduce the intensity of the output from the optical branching means 3 of
At least one of the input end and the output end of the optical amplification element 1 is provided with the second optical branching means 4 for introducing light from the outside.

[0007]

First, in the present invention, the semiconductor laser light amplification element is used as the light amplification element 1 to shorten the light amplification element 1, thereby shortening the operation time. The semiconductor laser light amplification element used as the light amplification element 1 can have an element length of 1 mm or less, and therefore the length of the entire ring resonator can be extremely shortened. In addition, integration with the optical coupler in the ring resonator is easy.

Next, in the present invention, since the semiconductor laser light amplification element does not have an abnormal amplification characteristic, the saturable absorber 5 is used.
The optical storage operation was realized by combining. As shown in FIG. 4, the saturable absorber 5 has a light transmission coefficient that varies depending on the intensity of incident light. When the light intensity is low, the transmittance is low, but when the light intensity is not lower than a certain level. In this case, the light transmittance is rapidly improved. There are various materials for the saturable absorber 5, and the saturable absorber 5 may be made of the same material as the semiconductor laser, for example. In this case, the saturable absorber 5 has a length of 1 mm or less, and the increase of the resonator length due to the addition of the saturable absorber 5 is slight. In addition, integration with the optical amplification element 1 in the ring resonator becomes easy.

Furthermore, in the present invention, since the semiconductor laser light amplifying element is used as the light amplifying element 1, the degree of freedom in selecting the oscillation wavelength is high. This is because the amplification center wavelength of the conventional optical amplification element A using a rare earth element-doped optical fiber is uniquely determined by the type of the rare earth element to be added, whereas the composition ratio of several elements is changed in the semiconductor laser optical amplification element. Because it can be set widely. In addition, the bandwidth that can be amplified is 30 to 30 in the optical amplification element using the rare earth optical fiber.
In contrast to 50 nm, the semiconductor laser light amplifying element can obtain a bandwidth near 100 nm by using the quantum well effect. This is one of the advantages of the present invention, considering that the optical logic circuit may be used in wavelength multiplexing.

Finally, in the present invention, as described later, by using the saturation phenomenon in the semiconductor laser light amplification element, the reset operation can be performed by light without adding a special mechanism.

The operation of the ring laser of the present invention will be described below (see FIGS. 1 and 5). In the initial state, the gain G of the optical amplification element 1 is smaller than the total loss L of the wavelength selection unit 2, the first optical branching unit 3, the saturable absorber 5, the second optical branching unit 4, and the isolator 6. Therefore, the gain of the entire resonator becomes negative and does not oscillate.

In this state, when the first light pulse (hereinafter also referred to as set light) is introduced from the outside via the second light branching means 4, the light transmission coefficient of the saturable absorber 5 rises,
The gain G of the optical amplifying element 1 is larger than the total loss L of the wavelength selecting unit 2, the first optical branching unit 3, the saturable absorber 5, and the second optical branching unit 4. And the optical amplification element 1
Starts to oscillate, continues to oscillate at the wavelength λs selected by the wavelength selecting means 2, and outputs light having a constant wavelength from the first optical branching means 3 to the outside. When it is desired to change the oscillating wavelength, the central wavelength of the wavelength selecting means 2 may be changed.

Once the optical amplifying device 1 has started to oscillate, even if the first optical pulse is not introduced from the outside, the saturable absorber 5 still maintains a high transmittance due to its own oscillation output. The laser oscillation is sustained.

When a second optical pulse (hereinafter, also referred to as reset light) different from the first optical pulse is introduced from the second optical branching means 4, it contributes to the amplifying action of the optical amplifying element 1. Since the number of internal carriers is reduced, the optical amplification element 1 is saturated and the output intensity of the optical amplification element 1 is reduced. Due to the decrease in the output intensity of the optical amplification element 1, the output from the first optical branching unit 3 also decreases.

[0015]

EXAMPLES Examples of the present invention will be described below. The optical amplification element 1 that amplifies light is a semiconductor laser optical amplification element that uses a semiconductor laser. In the present embodiment, the wavelength selection means 2 for receiving the light from the optical amplification element 1 and passing a certain wavelength is an optical filter in which an optical plate having a dielectric multilayer film deposited thereon is tilted with respect to the optical path. If an optical filter is used, the central wavelength of transmitted light can be changed by 20 nm or more. In addition, it is possible to use a diffraction grating. An optical coupler is used as the first optical branching means 3 for outputting the circulating light to the outside. Then, an isolator 6 for fixing the circulation direction of light is connected in a ring shape by an optical fiber to form a resonator. In this ring laser, the second optical branching means 4 is provided between the semiconductor laser light amplification element and the optical filter, and the optical duplexer 14 and the semiconductor laser light that can transmit light in the same device at the same time in mutually opposite directions without mutual interference. The optical coupler 24 is connected to the input end of the amplification element via the isolator 6. Further, the saturable absorber 5 whose light transmission coefficient is changed by the input light is provided. In this embodiment, the gain of the optical amplification element 1 is the loss of the entire loop, that is, the optical duplexer 14, the wavelength control means 2, the first optical branching means 3, the saturable absorber 5,
It oscillates when the total loss of the optical coupler 24 and the isolator 6 is exceeded.

Next, the operating principle will be described. (1) First, in the initial state, the output of the optical amplification element 1 is only weak noise light. Of this light, the light that matches the central wavelength λs of the wavelength selecting means 2 reaches the saturable absorber 5 via the first optical branching means 3. However, due to the characteristics of the saturable absorber 5, the transmission coefficient becomes small when the light that passes therethrough is weakened, and further the loss is caused, so that the optical amplification element 1
Does not reach the input end of. In this way, the total loss is larger than the gain of the optical amplification element 1, so that the state without oscillation output continues.

(2) Next, the oscillation state (also called a set state) will be described. An optical coupler 24 that constitutes a second optical branching unit 4 by a first optical pulse (hereinafter referred to as set light) that is light having the same wavelength as the oscillation wavelength λs of the optical amplification element 1.
When it is incident on the input end of the optical amplification element 1 through the isolator 6, it is amplified by the optical amplification element 1 and the wavelength selection means 2
Intense light is added to the saturable absorber 5 via the first light branching means 3 and the first light branching means 3. This light increases the light transmission coefficient of the saturable absorber 5, passes through the second optical coupler 24 and the isolator 6, and reaches the input end of the optical amplification element 1 again. This repetition causes oscillation.

(3) Once the oscillation is reached, even if the set light disappears, the saturable absorber 5 remains at a high transmittance due to its own oscillation output, and the oscillation continues. As a result, the oscillation state is maintained.

(4) Next, a method of resetting this set state will be described. Here, the reset light for resetting can operate even if it has the same wavelength as the circulating light or the set light. The reset light is introduced from the optical duplexer 14 to the output end side of the optical amplification element 1. Since the optical amplifier element 1 has an excessive input, the carriers that contribute to the internal amplification are reduced and the gain is reduced. At this time, the level of the oscillation output also decreases due to the decrease in gain, the light transmittance of the saturable absorber 5 also decreases, and the loss increases. In this way, the gain at the oscillation wavelength is reduced and the loss is increased, so that the oscillation of the entire resonator is stopped. Even if the reset light is removed, the loss of the saturable absorber 5 is large, so that the oscillation remains stopped and returns to the initial state.

In this case, the reset light is introduced to the output end side of the optical amplifying element 1 and circulates in the opposite direction to the light circling in the loop forming the resonator, and the reset light from the outside is circulated. Even if the wavelength λr is the same as the wavelength λs of the circulating light, the reset light does not appear at the output end of the first optical branching means 3. Further, since the reset light is not added to the saturable absorber 5 by the isolator 6, the transmittance of the saturable absorber 5 is not increased by this light. As a result, the set light and the reset light can operate even if they have the same wavelength, and when the logic circuits are used in a combination of multiple stages, there is no need to control the wavelength variable means 2 in each stage. is there.

Although common to the following embodiments, in this embodiment, since the semiconductor laser light amplifying element is used instead of the rare earth optical fiber, there is an advantage that the entire cavity length can be shortened.

Next, a second embodiment will be described with reference to FIG. In the second embodiment, the saturable absorber 5 is moved between the second optical coupler 24 and the isolator 6 in the configuration of the first embodiment. Next, the operation principle will be described.

(1) First, in the initial state, the output from the optical amplification element 1 is only weak noise light. Of this light, the light that matches the central wavelength λs of the wavelength selection means 2 is the first
It reaches the saturable absorber 5 through the optical branching means 3 and the second optical coupler 24. However, due to the characteristics of the saturable absorber 5, if the light that passes through is weak, the transmission coefficient becomes small, and the light is further received and does not reach the input end of the optical amplification element 1. In this way, the total loss of the ring resonator is larger than the gain of the optical amplification element 1, so that there is no oscillation output.

(2) Next, the oscillation state will be described.
When a slightly stronger set light is incident on the saturable absorber 5 from the second optical coupler 24, the light transmission coefficient of the saturable absorber 5 is increased by this light. Therefore, the above-mentioned weak λs component reaches the optical amplification element 1 through the saturable absorber 5 and is amplified. This repetition causes oscillation. Therefore, in this case, unlike the first embodiment, the wavelength of the set light does not necessarily have to be the same as λs.

(3) Once the oscillation is reached, even if the set light disappears, the saturable absorber 5 remains at a high transmittance due to its own oscillation output, and the oscillation continues. As a result, the oscillation state is maintained. (4) Next, the method of resetting the set state is the same as in the first embodiment.

Next, a third embodiment will be described with reference to FIG. The third embodiment differs from the first embodiment in that only the second optical coupler 24 is used instead of the optical duplexer 14 and the second optical coupler 24 as the second optical branching means 4 for introducing light from the outside. Prepared Also in the third embodiment, as in the first embodiment, no oscillation occurs in the initial state. In this state, the optical amplification element 1 is passed through the isolator 6.
When the circulating light from the second optical coupler 24 connected to the input end side of the, and a set light of a different wavelength, that is, a so-called first optical pulse is incident, the optical pulse is amplified by the optical amplification element 1,
Strong light is applied to the saturable absorber 5 through the wavelength varying means 2 and the first light branching means 3. This light increases the light transmission coefficient of the saturable absorber 5, passes through the second optical coupler 24, reaches the input end of the optical amplification element 1 again, and oscillates. Once
When the oscillation is reached, even if the set light disappears, the saturable absorber 5 remains at a high transmittance due to its own oscillation output, oscillation continues, and the oscillation state is maintained. Here, when the second optical pulse having a different wavelength λr from the first optical pulse is introduced from the second optical coupler 24, the optical amplifier device 1 is saturated and the gain is reduced due to excessive input. At this time, the level of the set light is also lowered due to the decrease in gain, and the saturable absorber 5
The light transmittance of is also decreased and the loss is increased. In this way, the gain for the set light is reduced and the loss is increased, so that oscillation as a loop is stopped. Even if the reset light is removed, the loss of the saturable absorber 5 is large, so that the oscillation remains stopped and returns to the initial state.

In the third embodiment, it is necessary that the reset light from the outside and the circulating light have different wavelengths.
This is because, if the wavelength of the reset light is the same as the oscillation wavelength, it will be output to the outside via the wavelength selecting means 2 and the first optical branching means 3. Since the reset light from the outside has a different wavelength from the circulating light, the wavelength selection means 2
It is cut by and does not appear at the output end of the first optical branching means 3.

In the third embodiment, the set light and the reset light do not operate at the same wavelength, but there is an advantage that the structure is simple.

The ring laser of the above-described embodiment can easily form a logic circuit such as a flip-flop.

[0030]

The effects of the present invention can be summarized as follows. (1) First, in the present invention, a semiconductor laser light amplification element is used as the light amplification element to shorten the length of the light amplification element, thereby shortening the operation time. The semiconductor laser light amplifying element used as the light amplifying element can have an element length of 1 mm or less, and therefore the length of the entire ring resonator can be extremely shortened. (2) Next, in the present invention, since the semiconductor laser light amplification element is used as the light amplification element, the degree of freedom in selecting the oscillation wavelength is high. (3) Finally, in the present invention, by using the saturation phenomenon in the semiconductor laser light amplification element, the reset operation can be performed by light without adding a special mechanism.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram showing characteristics of a saturable absorber.

FIG. 5 is a diagram showing a timing chart of the operation of the ring laser of the present invention and the optical storage device of the prior art.

FIG. 6 is a diagram showing a structure of a conventional optical storage device.

FIG. 7 is a diagram showing an abnormal amplification characteristic.

FIG. 8 is a diagram showing characteristics of a conventional optical storage device.

[Explanation of symbols]

 1 Optical amplification element. 2 Wavelength selection means. 3 First light branching means. 4 Second light splitting means. 5 Saturable absorber. 6 Isolator. 14 Hikari duplexer. 24 Second optical coupler.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01S 3/18 // G02B 27/28 A 9120-2K

Claims (1)

[Claims] 1. An optical amplification element (1) and a wavelength selection means (2).
And a first optical branching means (3) for outputting circulating light to the outside and an isolator (6) connected in a ring shape to form a resonator, wherein the optical amplification element is a traveling waveform semiconductor. A saturable absorber (5), which is composed of a laser light amplification element and has a light transmission coefficient that changes depending on the input light, and a first optical pulse of the output of the first optical branching means when the first optical pulse is introduced. The input end and the output end of the optical amplifying element are arranged so as to increase the intensity and decrease the intensity of the output of the first optical branching means when the second optical pulse which is delayed from the first optical pulse is introduced. A ring laser comprising a second optical branching means (4) for introducing light from the outside to at least one of them.