JPH02148784A - Optically bistable type semiconductor laser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] (Summary) The present invention relates to a bistable semiconductor laser whose oscillation darkness value changes depending on the input of external light. The purpose of this invention is to realize an optical bistable laser with a structure in which a saturable absorption layer is provided over the entire length of the active layer of a semiconductor laser at a position close to the active layer within the light seepage distance.

Because the saturable absorbing layer is tightly coupled to the active layer,
Even if the level of light incident on the saturable absorption layer is low, the oscillation darkness value of the laser can be shifted, achieving highly sensitive optical bistability.

[Industrial application field]

The present invention relates to a bistable semiconductor laser whose oscillation darkness value changes depending on the input of external light.

In a semiconductor laser, the light generated by the recombination of electron/hole pairs generated by current injection is resonated in a guide layer constructed by utilizing the difference in refractive index, resulting in laser oscillation.The optical output for a given current value is Although it is usually determined centrally,
By adopting a special structure, it is possible to provide hysteresis in the optical output characteristics with respect to the injected current.

An example of such a semiconductor laser is shown in FIG. Figure (a) is a schematic diagram showing a cross section cut perpendicularly to the length direction of the laser guide layer, and as shown in Figure 3), it is a diagram cut along the X-7 plane. It is.

The laser shown in FIG. 4 differs from the usual one in that it has two anode electrodes, and these electrodes generate mutually independent currents. , r, can be injected.

Further, there is a portion of the active layer 3 between the picture electrodes into which no excitation current is injected, and this portion functions as a saturable absorption region.

The laser with the above structure operates as follows. First, the current I,
, The relationship between the start and end of laser oscillation due to I2 is shown in Figure 5 (
It is like a). 11 or when I2 is increased, laser oscillation starts when the current exceeds the boundary line T1, but when the current is then decreased, the oscillation state is maintained even when the current becomes below T1, and becomes below T2. However, the oscillation stops.

To be more specific, for example, if we consider the case of keeping I2 constant and changing I1, as shown in straight line B in Figure (a), we can gradually change It from 0 as shown in Figure (b). If the current is increased, laser oscillation occurs when the current exceeds Ill,
When the current is reduced to below It2, oscillation stops.

In other words, a hysteresis loop exists in the diagram showing the relationship between excitation current and light output.

The laser also has oscillation characteristics that change depending on external light input. For example, if the current condition is fixed at point P in Figure 5(a) and light is input from the end face of the active layer, the relationship between the optical input level and the output level of the oscillated light is as shown in Figure 5(C). Become something. That is, when the optical input is O or weak, it is in a non-oscillating state, but as the optical input level increases, LL
When the value exceeds 1, the state changes to oscillation and optical output appears. - Once in the oscillation state, the oscillation state is maintained even if the optical input is removed.

In this way, the laser can be switched between non-oscillation and oscillation by optical input, and once it enters the oscillating state, it remains in the oscillating state even if the optical input is removed, making this type of laser optically bistable. It's called a laser.

[Prior art and problems to be solved by the invention] In the laser with the structure shown in FIG. 4, which is conventionally known as an optical bistable laser, in order to lower the optical input level for transitioning to the oscillation state, it is necessary to In order to increase the sensitivity, it is necessary to make the saturable absorption region longer.

However, if only the saturable absorption region in the structure shown in FIG. 4 is lengthened, the width of the hysteresis of the device becomes wide, and the optical output characteristics as a laser deteriorate. Furthermore, since the active layer also functions as an optical resonator, it is also disadvantageous to make its total length extremely long.

Due to these circumstances, the current situation is that several hundred microwatts of optical input is required for transitioning to the oscillation state.

An object of the present invention is to provide a bistable laser with improved optical input sensitivity by improving the element structure.

[Means to solve the problem]

In order to achieve the above object, the optically bistable semiconductor laser of the present invention has a saturable structure that is independent of the active layer by being close to the active layer within the light seepage distance over the entire length of the active layer in the optical resonance direction. An absorbent layer is provided.

[For production]

FIG. 1 is a schematic diagram showing the principle of the structure of the semiconductor laser of the present invention. The point that an active layer 3 is provided between a substrate 1 including a bumper layer and a cladding layer 4 is the same as in a normal semiconductor laser, but in the laser of the present invention, a cladding layer 4 is sandwiched between the active layer 3 and light leakage from the active layer 3. A saturable absorption layer 5 is provided at a position within the extension distance. In other parts of the figure, 6 is a cladding layer, 8 is a p-electrode, and 9 is an n-electrode. External light is input into the saturable absorption layer 5.

When a saturable absorption layer is provided as shown in the figure, the external input light is effectively absorbed by the saturable absorption layer due to its long length, which has a large effect on the laser oscillation of the active layer. . This point can be understood as follows.

First, the absorption rate of the saturable absorption layer changes with respect to the optical input level as shown in FIG. Since the effect on laser oscillation is the product of the amount of change in absorption rate and the volume of the saturable absorbing layer, a larger volume of the saturable absorbing layer will show the same effect with a smaller change in absorption rate. become.

That is, when a larger saturable absorption layer is provided, laser oscillation is started with an optical input that changes the absorption rate up to, for example, point 19 in the same figure, whereas when the saturable absorption layer is smaller, laser oscillation is started. would require an optical input that changes the absorption rate up to, for example, 22 points. Note that in order for the saturable absorption layer to exhibit an effect on the active layer in the structure shown in FIG. 1, it is necessary that the two be close to each other within the light seepage distance.

〔Example〕

FIG. 3 is a schematic cross-sectional view showing the structure of an element according to an embodiment of the present invention. The structure will be described below, including an example of the formation method.

A buffer layer 2 of the same <n-InP is epitaxially grown to a thickness of 2 μm on the n-TnP substrate 1, and further Inc
An active layer 3 of aAsP is epitaxially grown to a thickness of 0.15 μm. The composition of the quaternary compound is 1.55μ in terms of wavelength.
It is m. All of the compound semiconductor layers discussed in the following description are also formed by epitaxial growth.

A cladding layer 4 made of p-InP is formed on the active layer with a thickness of 1°5 μm.
A saturable absorption layer 5 is grown thereon to a thickness of 0.15 μm. The saturable absorption layer is the same as the active layer, and is made of lnGaAsP with a converted wavelength of 1655 μm, and is doped with p-type impurities.

1.5u of p-1nP ground layer 6 on the saturable absorption layer
A contact layer of p''-1n GaAsP is deposited to provide a P electrode 8. Further, an n electrode 9 is provided on the substrate side.

The device of the embodiment has the above structure, and its operation is as explained in the operation section.

〔Effect of the invention〕

As explained above, the optical bistable semiconductor laser of the present invention has increased sensitivity to optical input without sacrificing its laser characteristics, and can rapidly transition between two states. ing.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the basic structure of the device of the present invention. FIG. 2 is a diagram explaining the action of the saturable absorption layer. FIG. 3 is a schematic cross-sectional diagram showing the structure of the device of the embodiment. FIG. 5 is a cross-sectional schematic diagram showing the structure of a conventional optical bistable laser. In the figure, ■ is a substrate (n-1nP), and 2 is a buffer layer ( 3 is an active layer (InGaAsP), 4 is a cladding layer (p-1nP), 5 is a saturable absorption layer (p-1nGaASP), 6 is a cracito layer (p-1nP), 7 is a contact layer ( 8 is a p-electrode, and 9 is an n-electrode. A schematic diagram showing the basic structure of the device of the present invention. A diagram explaining the action of the optical input saturable absorption layer. Schematic cross-sectional diagram showing the structure Figure 1 Schematic cross-sectional diagram showing the structure of a conventional optical bistable laser

Claims (1)

[Scope of Claims] An active layer is provided as a region in which laser oscillation is performed by current injection; An optical bistable semiconductor laser characterized by being provided with a saturated absorption layer.