JPH02291534A - Bistable optical circuit - Google Patents

Abstract

PURPOSE:To obtain bistability between the frequency of input light and the frequency of output light by utilizing the light frequency-light intensity bistability of a nonlinear Fabri-Perot resonator and the input light intensity-output light frequency conversion characteristic of a single oscillation semiconductor laser. CONSTITUTION:The structure parameters of the nonlinear Fabri-Perot resonator 11 are so set that the bistability is obtained between the frequency of the light L1 and the output light L2. The single oscillation semiconductor laser 12 oscillates with single wavelength and varies in oscillation frequency according to the input of the output light L2 of the nonlinear Fabri-Perot resonator 11 to output light L3 based upon the frequency variation. Namely, the single oscillation semiconductor laser 12 has the input light intensity-output light frequency conversion characteristic. Thus, it is evident from the relation between the frequency of the input light L1 to the nonlinear Fabri-Perot resonator 11 and the frequency of the output light L3 of the single oscillation semiconductor laser 12 that the bistability is present between the input light frequency and output frequency.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to optical bistable circuits used in optical logic circuits, and particularly to optical bistable circuits in which the output optical frequency exhibits bistable characteristics with respect to the input optical frequency. It is related to circuits.

(Prior Art) FIG. 2 is a block diagram showing a conventional example of an optical bistable circuit. In FIG. 2, a half mirror 3 1.2 is a nonlinear medium 3 whose refractive index changes depending on the light intensity. The basic structure of this optical bistable circuit is a nonlinear Fabric resonator in which a nonlinear medium is inserted between two opposing half mirrors 1 and 2.

As the nonlinear medium 3, in addition to a normal optical Kerr medium such as cs'2 or LiNbo3, a nonlinear amplification medium such as an optical semiconductor amplifier can be used.

In such a configuration, for example, light of a single frequency is input from the left side of the half mirror 1 as viewed from the drawing, and is output to the right side of the half mirror 2. Then, if the values of the resonator length, reflectance of the half mirror, input light intensity, etc. are set appropriately, the input light intensity vs. output light intensity and The relationship between the input optical frequency and the output optical intensity is shown in (a) in Fig. 3, respectively.
) and (b) are known to exhibit hysteresis characteristics. The horizontal axis in (a) of Figure 3 represents the input light intensity, and the vertical axis represents the output light intensity.
) represents the input optical frequency, and the vertical axis represents the output optical intensity.

In the case of (a) in Figure 3, the position of the jump point depends on the resonator length, the reflectance of the half mirror, etc.
In some cases, there is no hysteresis and there is simply a jump at the same point.

In the case of FIG. 3(b), the position of the jump point depends on the input light intensity, the reflectance of the mirror, etc., and there are cases where the jump only occurs at the same point.

This type of input/output characteristic is called bistability because there are two stable states for the same human-powered state.

The structure shown in FIG. 2 is not the only one that exhibits bistability. For example, even in a system in which light is input from the outside to a semiconductor laser having a divided electrode structure, bistability appears depending on the conditions. In this case, if you increase the input light intensity,
If it jumps to an oscillation state at a certain point and conversely weakens the input light intensity, it jumps to a non-oscillation state at a different input light intensity level from the jump point to the oscillation state, causing hysteresis.

Also, in an optical injection locking system in which light with a frequency slightly different from the oscillation frequency is externally injected into an oscillating semiconductor laser, bistability appears depending on the conditions. In this case, hysteresis occurs in the state of attraction between synchronous and asynchronous states when the injection light intensity or the injection destination frequency is changed, and bistability is exhibited.

Three conventional examples of optical bistable circuits have been listed above. In the nonlinear Fabric resonator type shown in FIG. 2, bistability appears in the output light intensity, and its frequency is the same as the input light frequency.

Furthermore, in the split electrode semiconductor laser type, bistability also appears in the output light intensity, and the frequency is fixed to the oscillation frequency of the split electrode semiconductor laser.

Furthermore, since the injection-locked type jumps between the same and asynchronous states, both the output light intensity and the output light frequency exhibit bistability.

What these optical bistable circuits have in common is that they exhibit bistability in terms of output light intensity. Therefore, these circuits can be used in optical logic circuits that turn the light intensity on and off at "1" and "0".

On the other hand, when using light as an information carrier, it is possible to carry information not only in intensity but also in frequency. That is, f
It is also possible to send information by setting the two optical frequency states l and fO as "1" and "0". Therefore, an optical logic circuit using optical frequencies is also considered.

(Problems to be Solved by the Invention) However, each of the conventional optical bistable circuits described above has the drawback that the output light intensity is turned on and off, and cannot be applied to optical logic circuits that utilize optical frequencies.

The present invention has been made in view of such circumstances, and its purpose is to be able to exhibit bistability between input optical frequency and output optical frequency, and to be applicable to optical logic circuits that utilize optical frequencies. The purpose of this invention is to provide an optical bistable circuit.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an optical bistable element that exhibits bistable characteristics H between an input optical frequency and an output optical intensity, and an output of the optical bistable element. a single-wavelength oscillation semiconductor laser in which light is manually input, and the wavelength of input light to the optical bistable element has a wavelength difference H to an extent that injection locking is not distorted with respect to the oscillation wavelength of the semiconductor laser, and , said '-1': set to be within the gain band of the gain medium in the conductor laser.

(Function) According to the present invention, light of a predetermined frequency is manually applied to the optical bistable element. The optical bistable element has a bistable characteristic between the input optical frequency and the output optical intensity, and outputs light based on this bistable characteristic.

Next, the output light of the optical bistable element is input into a single wavelength oscillation semiconductor laser which oscillates at a single wavelength. A single wavelength oscillation semiconductor laser has an oscillation frequency that changes depending on the intensity of input light, and outputs light based on the oscillation frequency.

The amount of change in the oscillation frequency of this single wavelength oscillation semiconductor laser is proportional to the input intensity. Now, the relationship of bistability is satisfied between the input light to the single wavelength oscillation semiconductor laser, that is, the output light intensity of the optical bistable element and the input optical frequency to the optical bistable element. .

Therefore, the circuit as a whole has bistability between the input optical frequency and the output optical frequency.

(Embodiment) FIG. 1 is a block diagram showing an embodiment of an optical bistable circuit according to the present invention. In FIG. 1, numeral 11 is a nonlinear Fabrypét resonator as an optical bistable element, which is equipped with an optical nonlinear medium, and 12 is a single wavelength oscillation semiconductor laser (hereinafter referred to as a single oscillation semiconductor laser). Also, Ll, L2 in the figure
, L3 are input light to the nonlinear Fabric resonator 11, output light from the nonlinear Fabric resonator 11,
That is, input light to the single oscillation semiconductor laser 12 and output light from the single oscillation semiconductor laser 12 are shown.

Here, input light L1 to the nonlinear Fabry resonator 11
Based on the principle described later, the wavelength has a wavelength difference to the extent that no injection interval is applied to the oscillation wavelength of the single-oscillation semiconductor laser 12, and the wavelength of the single-oscillation semiconductor laser 12 (laser resonator) The gain is set to be within the gain band of the hostage.

At this time, due to the characteristics of the nonlinear Fabry resonator 11,
The wavelength of the output light L2 is the same as the wavelength of the input light L1.

The nonlinear Fabric resonator 11 exhibits bistability between the input optical frequency and the output optical intensity under appropriate conditions. Fourth
(a) in the figure shows its input/output characteristics.

In FIG. 4(a), the horizontal axis represents the frequency of the input light L1 to the nonlinear Fabric resonator 11, and the vertical axis represents the intensity of the output light L2 from the nonlinear Fabric resonator 11.

That is, the structural parameters of the nonlinear Fabric resonator 11 are set so that bistability as shown in FIG. 4(a) appears between the frequency of the input light Ll and the output light L2. There is.

The single-oscillation semiconductor laser 12 oscillates at a single wavelength, and the oscillation frequency changes according to the input of the output light L2 of the nonlinear Fabric resonator 11, and outputs light L3 based on this. That is, the single-oscillation semiconductor laser 12 has an input light intensity-output light frequency conversion characteristic of H.

FIG. 4(b) shows the relationship between the frequency of the input light L1 to the nonlinear Fabry-Pét resonator 11 and the frequency of the output light L3 of the single-oscillation semiconductor laser 12. Figure 4 (b)
, the horizontal axis represents the frequency of the input light Ll to the nonlinear Fabry-Pét resonator 11, and the vertical axis represents the frequency of the single-oscillation semiconductor laser 12.
respectively represent the frequencies of the output light L2. This fourth
(b) of the figure shows that the optical bistable circuit in FIG. 1 has bistability between the input optical frequency and the output frequency.

Next, the input light intensity-output light frequency conversion characteristic when light is manually applied from the outside to the single-oscillation semiconductor laser 12 in the oscillation state will be described in detail.

When a semiconductor laser oscillating at a single wavelength is externally inputted with light at a wavelength different from the resonant wavelength, injection locking occurs if the wavelength of the externally input light is very close to the oscillation wavelength.
The oscillation wavelength matches the wavelength of external input light.

On the other hand, if the wavelength of the external input light has a certain wavelength difference from the oscillation wavelength, the oscillation wavelength will hardly change, but the wavelength of the external input light will be Within the gain band of the medium, some shift in the oscillation frequency occurs depending on the external input light intensity.

This is due to the following mechanism.

When light with a wavelength that is far enough away from the oscillation wavelength to prevent injection locking and is within the gain band of the laser amplification medium is input, the light interacts with electron carriers within the semiconductor laser. and induces stimulated emission. This reduces the number of electron carriers within the semiconductor laser. It is known that when the number of electron carriers in a semiconductor laser decreases, the refractive index of the semiconductor medium increases. When the refractive index changes, the resonant frequency of the laser resonator changes, which changes the oscillation frequency.

That is, the semiconductor laser oscillation frequency changes depending on the external input light. The amount of change in the oscillation frequency is proportional to the amount of change in the refractive index, the amount of change in the refractive index is proportional to the intensity of stimulated emission, and the intensity of stimulated emission is proportional to the intensity of input light. Therefore, the amount of change in the oscillation frequency is proportional to the input light intensity. Note that although light externally input to a semiconductor laser causes stimulated emission to some extent, it is not amplified significantly because it is far from the resonant frequency of the laser resonator, and almost no light appears at the output end of the semiconductor laser. do not have.

The single-oscillation semiconductor laser 12 obtains the output light L3 using the above-described principle, that is, the change in oscillation frequency due to external input light. Therefore, as described above, the wavelength of the input light Ll to the nonlinear Fabry-Pét resonator 11 has a wavelength difference with respect to the oscillation wavelength of the single-oscillation semiconductor laser 12 to the extent that injection locking is not applied, and It is set to be within the gain band of the gain medium in the semiconductor laser 12 (laser resonator).

Next, the operation of the above configuration will be explained.

First, the light LL of a predetermined frequency is input to the nonlinear Fabric resonator 11 . Nonlinear Fabric resonator 11
is between the input optical frequency and the output optical intensity (a
), and outputs light L2 based on this bistable characteristic.

Next, the output light L2 of the nonlinear Fabric resonator 11 is
The signal is input to a single-oscillation semiconductor laser 12 that oscillates at a single wavelength.

The single oscillation semiconductor laser 12 has an oscillation frequency that changes depending on the intensity of the input light L2, and outputs light L3 based on the oscillation frequency.

The frequency of this output light L3 is determined by the above-mentioned mechanism.
It is proportional to the intensity of input light L2. Now, there is a difference between the intensity of the input light L2 to the single-oscillation semiconductor laser 12, that is, the output light L2 of the nonlinear Fabbribe resonator 11, and the frequency of the input light Ll to the nonlinear Fabbribe resonator 11. Since there is a relationship as shown in FIG. 4(a), the frequency of the input light Ll to the nonlinear Fabbribe cavity 11 and the frequency of the output light L3 of the single-oscillation semiconductor laser 12 are as shown in FIG. 4(b).
The relationship shown in is satisfied.

Therefore, if Ll is the input light to the entire circuit and L3 is the output light from the entire circuit, bistability will appear between the input optical frequency and the output optical frequency.

As explained above, according to this embodiment, the bistability of the optical frequency versus optical intensity of the nonlinear Fabrypét resonator 11 and the input optical intensity-to-output optical frequency conversion characteristics of the single-oscillation semiconductor laser 12 can be utilized. This realizes an optical bistable circuit that exhibits bistability between the input optical frequency and the output optical frequency.

In this embodiment, the bistability of the optical frequency versus optical intensity of the nonlinear Fabric resonator 11 is utilized, but the present invention is not limited to this, and the optical injection-locked optical system described in the section of the prior art is used. Similar effects can be obtained using bistable circuits and other devices that have bistability in the input optical frequency vs. output optical intensity.

Further, in this embodiment, the nonlinear Fabry-Pét resonator 11 and the single-oscillation semiconductor laser 12 are directly connected, but they may be connected via an optical amplifier, an optical attenuator, or the like, if necessary.

(Effects of the Invention) As explained above, according to the present invention, an optical bistable element having bistable characteristics between an input optical frequency and an output optical intensity, and the output light of the optical bistable element are input. a single wavelength oscillation semiconductor laser, the wavelength of input light to the optical bistable element has a wavelength difference to an extent that injection locking does not occur with respect to the oscillation wavelength of the 16-conductor laser, and Since the configuration is set so that the gain band is within the gain band of the gain medium in the optical system, there is an advantage that an optical bistable circuit having bistability between the input optical frequency and the output optical frequency can be provided.

Therefore, in the fields of optical communication and optical information processing, there is an advantage that it can be applied particularly to optical logic circuits that utilize optical frequencies.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the optical bistable circuit according to the present invention, Fig. 2 is a block diagram of a conventional optical bistable circuit, and Fig. 3 is the input/output characteristics of the optical bistable circuit shown in Fig. 2. FIG. 4 is a diagram showing the relationship between the output light of each person in FIG. 1. 1, 2...Half Mihoo 3...Nonlinear medium,...Nonlinear Fabribet cavity, 2...Single wavelength oscillation semiconductor laser. Patent applicant Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] An optical bistable element having bistable characteristics between an input optical frequency and an output optical intensity, and a single wavelength oscillation semiconductor laser into which the output light of the optical bistable element is input, The wavelength of input light to the optical bistable element is set to have a wavelength difference with respect to the oscillation wavelength of the semiconductor laser to an extent that injection locking does not occur, and to be within a gain band of a gain medium in the semiconductor laser. An optical bistable circuit characterized by: