JPS6215873A - Optical bistable element - Google Patents

Abstract

PURPOSE:To decrease the driving current and increase the switching speed, by forming a medium which increases reflectivity at or near at least one end face of a semiconductor laser having a saturable absorber inside an optical resonator. CONSTITUTION:A medium which increases reflectivity is formed at or near at least one end face of a semiconductor laser having a saturable absorber inside an optical resonator. For example, an N<+>-InP clad layer 2, an InGaAsP optical active layer 3, an N<->-InP clad layer 4, a P-InP layer 5, 6, 7 having a P-type impurity diffused therein are formed on an N-type InP substrate 1. Further, an SiN insulating film 8 and an Au reflecting film 9 are provided. No current is injected into the center of the InGaAsP active layer 3 so that this region serves as a saturable absorber in the resonator. Thus, the reflectivity of the end face of the optical resonator is increased to increase the light feedback efficiency, thereby enabling saturation of the saturable absorber to be realized with a relatively weak light output, and thus allowing a bistable operation to be effected with a relatively small injection bias current. In addition, it is made possible to increase the switching speed.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an optical bistable device, and specifically, a saturable absorber is formed inside a semiconductor laser resonator, and a saturable absorber is formed in the resonator of a semiconductor laser. This invention relates to a bistable laser whose optical output can be switched on or off with a bias current within a certain range.

BACKGROUND OF THE INVENTION FIG. 4 schematically shows the structure of a conventional bistable semiconductor laser. 11 is an n-type InP substrate, 12 is an n+-InP epitaxial layer, 13 is an InGa layer, and 14 is an n-InP layer. 16 is a p-type impurity diffusion region, and 16 and 17 are electrodes. In this structure, no current is injected into the central part of the 13 rnGaAsp active layers, and this region is located within the resonator and acts as a saturable absorber.

FIG. 6 shows the optical output v, S, and current characteristics of the laser having this structure. In A, C, and C, the length Ls of the current non-injection region is 0.1°0.3 and 0 relative to the resonator length, respectively.
．． Case 5 is shown. In both cases, when the bias current is increased, the output increases rapidly when it exceeds a constant current (Step 2), and even if the current is decreased from that state, the output remains constant (
The ON state is maintained until the voltage drops below I, ). That is, it has a hysteresis characteristic, and by setting it between the bias current e11 and the bias current e11, a bistable state can be realized.

Switching from the OFF state to the ON state is
This can be achieved by adding a positive current pulse to the bias current, and reverse switching can be achieved by adding a negative pulse. There is a strong relationship between switching speed and hysteresis width, and the larger the hysteresis width, the faster switching is possible.

Problems to be Solved by the Invention Conventionally, a method of increasing the area of the saturable absorber has been considered as a method of increasing the width of hysteresis, but as is clear from the results in FIG. This resulted in an increase in operating current, which was a big problem in practice.

The present invention is intended to solve the above-mentioned problems, but rather to reduce the drive current and increase the switching speed.

Means for Solving the Problems The present invention provides an optical bistable device in which a medium for increasing reflectance is formed at or near at least one end face of a semiconductor laser having a saturable absorber inside an optical resonator. It is.

Effect 1 FIG. 6 shows the change in process 1 and (I2 L)/II when the reflectance of the laser end face in A in FIG. 5 is changed. As is clear from this figure, as the end face reflectance H increases, the bistable operating current decreases, and the width of the hysteresis with respect to the operating current also increases. Therefore, the principle of the present invention is to increase the light feedback efficiency by increasing the end face reflectance of the optical resonator, so that the saturation of the saturable absorber can be achieved even with a weak optical output. As a result, bistable operation is possible with a small injection bias current, and the switching speed is increased.

Embodiment FIG. 1 schematically shows a bistable laser in an embodiment of the present invention. 1 is an n-type engineered nP substrate, 2 is a total InP cladding layer, 3 is an InGaAsP photoactive layer, and 4 is an n-InP
The cladding layer 6 is p-InP diffused with p-type impurities.
Layers 6 and 7 are electrodes. This structure is similar to the conventional structure, but in this embodiment, an SiN insulating film 8 and an Au
A reflective film 9 is added.

FIG. 2 shows the current-optical output characteristics (b) of the semiconductor bistable laser of this embodiment and the characteristics (e) of the conventional laser. It is confirmed that by applying a reflective film to the end face, it is possible to lower the operating current. The end face reflectance is approximately 96
%it is conceivable that.

Further, FIG. 3 shows all the response characteristics of the laser of this embodiment (FIG.) and the conventional example (G). In both cases, the bias current was set in hysteresis, and a current pulse of Q, 'lnS was applied at a peak approximately 10 times the threshold current. Conventionally, it took about 3 nS to reach a steady state, but in the laser of this embodiment, it took about 2 nS, which shows that the response speed has also been improved.

Effects of the Invention As described above, the present invention increases the operating current by adding a simple step of installing a light reflector near the end face of a conventional semiconductor bistable laser. This greatly reduces the response speed and improves the response speed.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the entire schematic structure of a bistable semiconductor laser according to an embodiment of the present invention, and FIG. 2 is a comparison of the current-light output characteristics of the same bistable semiconductor laser with the characteristics of a conventional device. Figure 3 shows the response characteristics of the bistable semiconductor laser and the characteristics of a conventional device, and Figure 6 shows the current-optical output characteristics of the stable semiconductor laser. FIG. 3 is a diagram showing a predicted hysteresis width and a change in threshold current when 1... Substrate, 2... Clad layer, 3...
...Active layer, 4...Clad layer, 6...
... p -I n P layer, 6, 7 ... electrode, 8 ... insulating layer, 9 ... reflective layer. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Fig. n-1 rtP Clad 1 Fig. 2 ;;:) 3],; Grass standing)

Claims (1)

[Claims] An optical bistable device comprising a semiconductor laser having an optically saturable absorber inside an optical resonator, and a medium for increasing reflectance formed at or near at least one end facet of a semiconductor laser.