JPH0277032A - Method for resetting bistable semiconductor laser and optical inverter - Google Patents

Abstract

PURPOSE:To reset a bistable laser with light with a moderate precision of wavelength by inputting incident light having a wavelength to be amplified in a gain region of a bistable laser from a light source for resetting to the bistable laser and causing consumption of a carrier in the gain region. CONSTITUTION:A bistable laser device provided with a bistable laser 1 and a resetting light source 2 is constituted. If the inputted light from the resetting light source 2 is coaxial with the laser light of the bistable laser 1, the wavelength of the inputted light is selected from a region where the absorption of saturable absorption region of light having a longer wavelength than a laser oscillation wavelength is not so strong. A carrier in a gain region of bistable laser 1 amplifies also the light other than those having a laser oscillation wavelength. When such light having a wavelength in an amplifiable wavelength region is inputted from outside, the inputted light is amplified in the gain region, and the carrier is consumed corresponding to an amt. used for the amplification, and laser oscillation is stopped due to decrease of the gain in the laser oscillation wavelength. Thus, bistable laser is reset easily by an optical signal.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for resetting a bistable semiconductor laser, it is an object of the present invention to provide a method for resetting a bistable laser with a new mechanism that can be reset by light with extremely gentle wavelength accuracy compared to conventional optical resetting. In order to achieve laser oscillation, the laser oscillation is achieved by injecting injection light of a wavelength that is amplified in the gain region into the gain region of a bistable semiconductor laser having a gain region and a saturable absorption region, and consuming the carriers in the gain region. Configure to reset.

[Industrial Field of Application] The present invention relates to an optical bistable device that performs optical signal processing, and particularly relates to a method for resetting a bistable semiconductor laser.

In recent years, as optical communications have become faster, instead of converting optical signals to electrical signals, processing the signals, and then converting them back to optical signals,
There is now a strong desire to process signals in the form of light.

Bistable elements are one of the elements necessary for such optical signal processing.
and its importance is increasing. Among these, bistable semiconductor lasers, in addition to optical bistability, have an amplification function themselves, and have a signal intensity ratio of 10, for example, when on/off.
It also has the advantage of being large, on the order of dB, and is a particularly useful element.

[Prior Art] Fig. 13 (A>, (B), and (C)) show bistable semiconductor lasers according to the prior art.
A laser resonator 50 is configured to include a gain region A and a saturable absorption region B. As for the internal structure, the gain region A and the saturable absorption region B include an n-type region 5 in the semiconductor chip.
1. An active region 52 and a p-type head region 53 are stacked.

In the gain region A, nlI]! on the n-type region 51a and the p-wall region 53a! I electrode fli 54 and P side electrode 55 are formed,
It has a structure in which stimulated emission occurs from the active region 52a by passing a current.

In the saturable absorption region B, at least one electrode is not provided so that no current flows. The active region 52b is made of the same material as the active region 52a of the gain region A, but
Since no current flows, there is no gain for light.

Figure 13 (B) shows the relationship between the carrier concentration in the active region and the gain (attenuation) at a certain wavelength below the gap wavelength. It has the property of absorbing energy (light). The attenuation characteristic on the left side of the graph corresponds to this.

When carriers are bombed (typically transitioned from the valence band to the conduction band) by passing a current,
The carrier concentration gradually increases. The increased carriers can emit light by performing luminescent recombination. Laser oscillation occurs by performing stimulated emission. This light-emitting function is stronger as the carrier concentration increases. Therefore, the gain for input light is negative (attenuation, light absorption) when the carrier concentration is low, but as the carrier concentration increases, it gradually increases and eventually becomes positive. As a result, it has an optical amplification function.

In the state of laser oscillation, a sufficient current flows through the gain region A, as shown by A in FIG. 13(B), and the gain region A has a positive gain g. However, in the saturable absorption region B, since no current flows, the gain at the oscillation wavelength is negative (absorption) as shown by B in FIG. 13(B).

The saturable absorption region B will be further explained with reference to FIG. 13(C). First, in the off state when the laser is not oscillating,
There are few carriers and light absorption is strong. When the light emitted in the gain region A enters the saturable absorption region B, the saturable absorption region B absorbs this light and photoexcited carriers are generated. As the intensity of the incident light increases, the number of carriers excited by the light increases and the probability of radiative recombination of the carriers also increases. Therefore, as the carrier concentration increases, the absorption decreases and the gain approaches zero from the negative side. However, since the saturable absorption region B has no other side of the bombing a, the gain is positive at the wavelength of the incident light. The region where such optical absorption saturation occurs is called the saturable absorption region.
In the on state where laser oscillation is occurring, the amount of incident light is large, so the carrier concentration is high, and absorption is weaker than in the off state.

The characteristics of a bistable semiconductor laser will be explained using FIG. 14 (A). In FIG. 14 (A), the horizontal axis shows the drive current and the vertical axis shows the optical output. As the M-cutting current is increased, Although the carrier concentration in the gain region increases, the saturable absorption region is in a state of strong absorption, so laser oscillation does not occur easily. When the current reaches the lasing threshold Ith, laser oscillation begins and high-intensity laser light becomes saturable. It also enters the absorption region.As a result, carriers are excited in the saturable absorption region, and light absorption is reduced as shown in Fig. 13(C).Therefore, to a certain extent, even if the current is lowered below the open circuit Ith, sufficient light intensity can be obtained. The laser oscillation is ensured and the oscillation continues.Laser oscillation stops only when the current 1 falls to the off value 1off.Then, the saturable absorption region returns to a state of strong absorption.Therefore, the current is kept below the off value 1off to a certain extent. Laser oscillation does not start even if the current exceeds the open chain Ith.At the current value between Ioff and Ith, there are two stable states: on and off.In this way, the saturable absorption region Semiconductor lasers exhibit hysteresis characteristics and can assume a bistable state with respect to optical output.

Figure 14 (B) shows the electrical reset of a conventional bistable laser.
Explain with reference to. The current 1b is set to an intermediate value between the on time [1th] and the off value Ioff. At this current value, the optical output has two stable states: ON state S1 and OFF state S2. Now, assuming that the optical output is in the ON state S1, a pulse of negative polarity is applied to reduce the current to a value lower than the OFF value Ioff. lower to the value. The laser is then turned off. Thereafter, the current value is returned to the state Ib satisfying Ioff<Ib<rth, and the laser remains off S2. In this way, the laser is electrically reset by a current pulse having a negative polarity with respect to the bias value rb.

Setting may be performed by a positive current pulse having a value equal to or higher than the open chain Tth, or may be performed by injecting excitation light having a wavelength close to the oscillation wavelength.

Recently, a method has been proposed to bring a bistable laser into a beat state and reset it using adjacent wavelengths (Spring 1988, Japan Society of Applied Physics, lecture number 30p-Zl-(-14), two lights with adjacent wavelengths This method utilizes the ability to interfere with each other to create a beat.

This operation can be thought of as follows.

Referring to FIG. 15, when the two frequencies are extremely close, the overall optical output changes to follow the beat frequency. When the optical output decreases beyond a certain level, carrier bombing in the saturable absorption region decreases. Therefore, the carrier concentration decreases,
As shown in FIG. 15(B), the light absorption becomes strong. If the light absorption becomes strong beyond a certain point, the laser oscillation cannot be maintained and the laser is reset to the OFF state.

[Problems to be Solved by the Invention] The method of electrically resetting a bistable laser requires the use of an electrical signal for control, and if high-speed resetting is attempted, electrical noise will be generated in the surrounding area. Particularly in integrated devices, crosstalk occurs between electrical wiring.

The method of resetting a bistable laser by causing beat oscillation by injecting light with a wavelength very close to the laser oscillation wavelength requires that the carrier motion follow the period of the beat oscillation, so 0.1 Å
The wavelength of the injected light must be controlled with extremely high precision, with a wavelength difference of:

As described above, according to the prior art, only electrical reset or optical reset, which requires extremely high precision, can be performed.

An object of the present invention is to provide a new method for resetting an m-tree bistable laser, which can be reset by light with extremely loose wavelength accuracy compared to conventional optical resetting, and an apparatus for implementing the method.

Another object of the invention is to provide an optical power inverter that is optically reset.

[Means for solving the problem] Referring to FIG.
Injected light having a wavelength that is amplified in the gain region of the bistable laser 1 is input from the bistable laser 1, and the bistable laser is reset by consuming carriers in the gain region.

A bistable laser device including such a bistable laser 1 and a reset light source 2 is configured.

When the injection light from the reset light source is coaxial with the laser beam of the bistable laser, the wavelength of the injection light is selected from a region where absorption in the saturable absorption region with a wavelength longer than the laser oscillation wavelength is not strong.

A bistable laser that is reset by such an optical signal is used to configure an optical inverter whose optical output is inverted depending on the optical input.

[Operation] Carriers in the gain region of a bistable laser can amplify light other than the laser oscillation wavelength.

When light with a wavelength within a wavelength range that has such an amplification function is injected from the outside, this injected light is amplified in the gain region, and the number of carriers in the gain region decreases by the amount used for amplification. This reduces the gain at the laser oscillation wavelength and stops laser oscillation. The amplified injection light is output, but when the injection light is turned off, the total optical output is also turned off.

When the injection light and the laser oscillation light are coaxial, the injection light also irradiates the saturable region. When the wavelength of the injected light is shorter than the laser oscillation wavelength, light absorption in the saturable absorption region is strong, and the injected light is mainly consumed in generating carriers in the saturable absorption region. Laser oscillation becomes stable due to the reduced optical absorption. By using a wavelength that is not absorbed much in the saturable absorption region and is amplified in the gain region, carriers are consumed in the gain region and the laser oscillation is reset. can. For this reason, in the case of a coaxial system, the wavelength of the injected light is preferably selected from a wavelength region longer than the laser oscillation wavelength.

If the injected light and the laser oscillation light are on different axes, the injected light can be directed only toward the gain region, and the wavelength of the injected light can be selected to be amplified in the gain region, thereby reducing the laser oscillation light and resetting the oscillation. can.

In the case of an optical inverter, a state "1" with injected light causes a state "o" with no output light, so it functions as an inverter for optical signals.

[Example 1] Figure 2 shows the case where the setting light is coaxial with the wavelength light of the bistable semiconductor laser. As shown in the schematic diagram above in Figure 2, the injected light is incident parallel to the active layer. do.

The lower graph in FIG. 2 is a spectrum of gain versus wavelength (or energy) of the bistable laser 1 at a certain current density. When the current intensity is decreased, the characteristics change from a solid curve to a dashed curve to a dashed-dotted curve. For the gain on the vertical axis, the positive side above 0 means amplification,
A negative value below 0 means absorption. In a region where the gain is positive, once stimulated emission occurs, laser oscillation may continue.

By the way, a bistable semiconductor laser has a saturable absorption region in addition to a gain region. Since there are few carriers in the saturable absorption region, no amplification occurs, but light absorption occurs. Light absorption has wavelength dependence, and the shorter the wavelength, the stronger the light absorption becomes.

At wavelengths with strong optical absorption, even if light is injected from the outside, it will only be absorbed in the saturable absorption region.The laser oscillation wavelength is determined by balancing amplification by the gain region and absorption (attenuation) by the saturable absorption region. Due to the fact that λl is a fixed 0 oscillation, the absorption in the saturable absorption region is not excessively strong at the laser oscillation wavelength λl.If the wavelength is longer than the laser oscillation wavelength λ9, the absorption in the saturable absorption region becomes even weaker. . On the other hand, there is no substantial gain at wavelengths longer than the gap wavelength. Therefore, in the case of coaxial, a wavelength region with a gain that is longer than the laser oscillation wavelength, that is, a wavelength that is longer than the laser oscillation wavelength and shorter than the gap wavelength is suitable.

As shown in the upper schematic diagram of FIG. 3, which shows the case of different axes in FIG. 3, the injection light is made perpendicular to the active layer of the gain region, for example. The graph of gain versus wavelength at the bottom of FIG. 3 is equivalent to that of FIG.

In this case, since the injected light does not enter the saturable absorption region, there is no need to consider absorption in the saturable absorption region.

By injecting light at a wavelength with a certain gain into the gain region and performing an amplification action, carriers in the gain region are consumed, light at the laser oscillation wavelength is reduced, and the laser is reset.

The wavelength of the injected light only needs to be amplified in the gain region.
The wavelength in the region between the arrows in FIG. 3 is appropriate.

FIG. 4 shows a basic embodiment in the case of coaxial.

The bistable laser 1 has a set light source 4 and a reset light source 2.
The light from a is received via the multiplexer 6.

The setting light source 4 is a semiconductor laser that emits a trigger light that causes the bistable laser 1 current-biased to an intermediate state to oscillate as shown in FIG. 14(A). Consists of.

The reset light source 2a emits a trigger light that resets the laser oscillation of the bistable laser 1. In order to reset, it is necessary to consume carriers in gain region A and not to be strongly absorbed in saturable absorption region B. For example, in the range shown by the arrow in Figure 2, that is, longer than the laser oscillation wavelength and lower than the gap wavelength. It consists of a semiconductor laser that emits short wavelength laser light. Note that the distance from the laser oscillation wavelength of the bistable laser 1 is several angstroms or more.

The multiplexer 6 makes the set trigger light from the set light source 4 and the reset trigger light from the reset light source 2a coaxially enter the optical axis of the bistable laser 1.

The multiplexer 6 has a waveguide structure having, for example, two input ports and one output port, or a combination v1 of a half mirror or a sector mirror and a pond optical component.
It can be composed of ellipses.

The bistable laser 1 has a gain region A and a saturable absorption region B, has a zero steresis characteristic as shown in FIG. .

When the set trigger light is input from the set power source 4, the bistable laser 1 starts laser oscillation, and the reset light source 2a
When the reset light is inputted from the reset light, carriers are consumed to amplify the reset light, the laser oscillation light decreases, and the bistable radar 1 stops laser oscillation.

FIG. 5 shows a basic embodiment in the case of different axes. A bistable laser receives the trigger light from the setting light source 4 along the optical axis, and receives the trigger light from the reset light source 2b on a different axis from the optical axis. direction, for example, a direction perpendicular to the active layer. Since the set trigger light is incident along the optical axis, it is incident on both the gain region A and the saturable absorption region B of the bistable laser 1, but the reset trigger light is at an angle with the optical axis of the bistable laser. enters the gain region A, and enters the saturable absorption region B.
The reset light source 2b may be one that consumes carriers in the gain region A, for example, a semiconductor laser having an oscillation wavelength within the range of the arrow in FIG. 3, that is, the wavelength amplified in the gain region A. Can be configured. The setting light source 4 may be the same as the coaxial case shown in FIG.

In the embodiments shown in FIGS. 4 and 5, the bistable laser was set and reset using light, but the setting is not limited to this.

FIG. 6 shows an electrically set and optically reset embodiment, and the bistable laser 1 is the same as described above. When the set electrode 4b applies a positive current pulse to the bistable laser 1, the current exceeds the open chain Ith and the bistable laser 1
emits laser oscillation. When the gain region receives reset trigger light from the reset light source 2, the bistable laser 1 stops laser oscillation. The reset trigger light may be incident on the same axis to the bistable laser 1 as shown in FIG. 4, or may be incident on a different axis as shown in FIG.

A seventh bistable laser that can be used in the above embodiments is
As shown in FIG.

Figure 7 shows a coaxial bistable laser with a saturable absorption region B in the middle, a first gain region A1 on both sides, and a second gain region A.
It has 2.

An n-type InP cladding layer 12 is formed on an n-type 1nP substrate 11, and an InGaAsP active layer 14 and a p-type 1nP cladding layer 12 are formed on the n-type InP cladding layer 12.
P cladding layer 15, p+ type 1nGaAsP cap layer 1
6 is formed. The cap layer 16, the upper cladding layer 15, the active layer 14, so as to leave the active layer in a stripe shape.
A mesa etch is performed to the middle of the underlying cladding layer 12, and both sides of the mesa are filled with semi-insulating 1nP regions 18. A pfPI electrode 23 is formed on the substrate 11 via n measurement [i22] and selective SiO□ protection [21 on the surface of the cap layer 16 side. The stripes of the active layer 14 extend from the front in the drawing toward the back of the paper to form an optical axis. p(Pl electrode 2
3 is divided into a front part 23a and a rear part 23b,
A saturable absorption region B is defined in the middle. This bistable laser is suitable for use in a coaxial configuration embodiment such as that shown in FIG.

FIG. 8 shows a top view of a bistable laser suitable for use in an off-axis configuration embodiment such as FIG. 5, with the gain region A grouped into one region. Openings 25a, 25b, 25c without electrode 23 and p+ cap layer 16 in the gain region
Ill! is formed so that reset light can be injected into the active layer from above. has been completed.

It will be obvious to those skilled in the art that various conventionally known configurations can be used as the bistable laser and the mechanism for introducing light into the bistable laser, in addition to those described above.

The performance of a specific example of the embodiment of the coaxial configuration shown in FIG. 4 will be described below.

As the bistable laser 1, a Fabry-Bello type two-electrode type was used. The current flowing through the two electrodes is I, ■
Then, when l2 = 38.0 nA, I = 8.318 and on I = 6.0 nA as shown in FIG. 9(B). Bias current 1bof
f was set to 11 within the hysteresis, and the wavelength dependence of the light intensity required to turn the laser oscillation from the on state to the off state was measured. The results are shown in FIG. 9(A), where the horizontal axis shows the wavelength and the vertical axis shows the minimum light intensity required for resetting.The oscillation wavelength of the bistable laser 1 is 1°3023 μm, and here, .3150-1.3158 μm light was injected. The wavelength range that can be reset by light injection differs depending on the bias position, but when Ib is set to 6.11A, it can be reset in the entire wavelength range of the 8 people tested, and Ib
When Ib = 6.51A, it was possible to reset within the wavelength range of two people, and when Ib = 6.91A, it was possible to reset within the wavelength range of one person.

Figure 10 shows the signal waveform of the optical signal.The set light is 1.3
The wavelength of the reset light was 1.3154 μm. In addition, the respective injection light intensities are 30 μW and 90 μW.
Met. As the set light rises, the optical output of the bistable laser also rises, and when the reset light enters, a change appears in the output, and the optical output also falls almost simultaneously with the fall of the reset light.

Here, a Fabry Bellow type bistable laser was used and a single mode laser was used as the light source for the injection light, but a bistable laser with any resonator may be used, and the injection light source can also be multi-mode. It may also be one that oscillates in mode.

If the reset operation observed above is shown as a model, the 11th
The figure (A>-(D>) can be shown as follows. (A) is the optical input of wavelength λr which is the reset light, (B) is the optical output of wavelength λ' from the bistable laser, and (C) is The optical output of λl, which is the oscillation light wavelength of the bistable laser, and (D) indicate the total optical output from the bistable laser.

When the bistable laser is oscillating as shown in FIG. 11(C), the reset light of λr is incident as shown in FIG. 11(A). Then, the gain region of the bistable laser exhibits an amplification function for the reset light, and the light of λ' is amplified and output as shown in FIG. 11(B).For this reason,
The carriers are consumed, and as shown in FIG. 11(C), the optical output at the oscillation wavelength λl of the bistable laser disappears. The total optical output disappears when the light at the reset wavelength λ'' disappears, as shown in FIG. 11 (D>).

In this way, the bistable laser can be easily reset by the reset light.

FIG. 12 shows an optical output inverter that utilizes this operation.

The bistable laser 1 is set by a current pulse from the setting power source 4b or a light pulse from the cellar 1 to the circumferential light source 4, and is reset by a reset light pulse from the reset light source 2.

The set operation is automatically performed and the reset light pulse is used as the input signal. There is no reset light pulse that is the input signal (
0°°), the optical output is continuous (°1°°), and when there is a reset optical pulse as an input signal (“1”), the optical output is reset and disappears (“o’”). The optical signal inverter is configured as follows.

In the above embodiments, since light is used for the reset signal, there is no electrical crosstalk, which is effective in improving the degree of integration when integrated. Furthermore, since stimulated emission is used to reduce the carrier concentration, a reset time that is not limited by the carrier lifetime can be achieved. Furthermore, the precision of setting the wavelength of the injected light can be as low as several to several dozen or more people, making it possible to easily integrate ultra-high-speed optical bistable lasers at high density.

Although several embodiments have been described, it will be obvious to those skilled in the art that various combinations, changes, modifications, etc. can be made without departing from the spirit of the invention.

[Effect of the invention] Bistable lasers can be easily reset by optical signals.

An optical signal inverter can be configured.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the principle of the present invention. Figure 2 is a graph showing preferred wavelengths for coaxial configuration. Figure 3 is a graph showing preferred wavelengths for different axis configuration. Figure 4 is coaxial. FIG. 5 is a block diagram showing an optical set/reset bistable laser device with a different axis configuration. FIG. 6 is a block diagram showing an optical set/reset bistable laser device with a different axis configuration. A block diagram showing a stable laser device, FIG. 7 is a perspective view of a bistable laser for a coaxial configuration, FIG. 8 is a top view of a bistable laser for a different axis configuration, and FIGS.
B) is a graph showing the experimental results of an example of a coaxial configuration and a graph showing the bias conditions, FIG. 10 is a graph showing the optical output waveform, and FIGS.
FIG. 12 is a waveform diagram explaining the operation as a model, and FIG. 13 is a block diagram of the optical signal inverter.
C) is a diagram illustrating a bistable semiconductor laser according to the prior art, where (A> is a cross-sectional view showing the cross-sectional structure, (B) is a graph showing the dependence of gain on carrier concentration, and (C) is a diagram showing the saturable absorption region. 14 (A>, (B) are diagrams explaining electrical reset according to the prior art, (A) is a graph showing the characteristics of optical output vs. current, (B) is a graph showing the characteristics of the reset Waveform diagrams of current pulses, Figures 15 (A) and (B) are light beams according to the conventional technology.
FIG. 3A is a graph showing beats caused by light of adjacent wavelengths, and FIG. 3B is a graph showing gain changes in the saturable absorption region. In the figure 1 Bistable laser 8 Gain region B Saturable absorption region 2.2a, 2b Light source for reset 4 Light source for setting 4b Power source for center 6 Multiplexer, ・'', 1\\, A Gain region B Saturable absorption gi Range Tree Invention Principle Diagram Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 (A) Reset light intensity distribution (B)
Characteristics and bias Figure 9 50ns/div. Fig. 10 Reset operation by optical input Fig. 11 Optical signal inverter Fig. 12 (vague convergence) (B) Dependence of gain on carrier concentration

Claims (3)

[Claims] (1) Injecting light having a wavelength to be amplified in the gain region (A) into the gain region (A) of a bistable semiconductor laser having a gain region (A) and a saturable absorption region (B). A method for resetting a bistable semiconductor laser, characterized in that laser oscillation is reset by consuming carriers in the gain region (A). (2) The injected light is coaxially incident on the optical axis of the bistable semiconductor laser, and the wavelength of the injected light is the laser oscillation wavelength (λ
_l) The method for resetting a bistable semiconductor laser according to claim 1, wherein a longer wavelength is selected. (3) a bistable semiconductor laser (1) having a gain region and a saturable absorption region on the optical axis; means for setting the semiconductor laser (1) to an oscillation state; and a gain of the semiconductor laser (1). A reset light source (2) that injects injection light into the region (A), in which the wavelength of the injection light is different from the laser oscillation wavelength (λ_l) and is selected to be a wavelength amplified in the gain region; An optical inverter comprising: