JP2781211B2 - Optical logic element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an optical logic used in fields such as optical communication and optical information processing, which controls laser oscillation by injecting light from the outside into a semiconductor laser. It relates to an element.

(Prior Art) There is a method in which a semiconductor laser is used as a logic element in optical information processing and the oscillation extinction effect due to side injection light is used.

Conventionally, logic operation has been performed using two lasers, an oscillation laser and a quenching laser. FIG. 5 is an explanatory view thereof, in which 9 is a main laser oscillating, 10 is a quenching laser, and both are orthogonal to each other. Arrows indicate laser light. When the current is injected into the quenching laser 10 and the quench laser 10 is oscillated while the main laser 9 is oscillating, the gain of the main laser 9 decreases and the output of the main laser 9 decreases. In addition, laser 10 for quench
When the current injection to the main laser 9 is stopped, the main laser 9 returns to the original output state again. As described above, the logical operation becomes possible.

There is also an example of controlling laser oscillation by utilizing the fact that when TM-polarized light is incident on a semiconductor laser oscillating with TE polarization, the output of TE-polarized light is reduced.

However, when the main laser and the quenching laser are used, since the interaction region between the main laser and the quench laser is small, the ratio of the output decrease (extinction ratio) of the main laser when current is injected into the quench laser is reduced. small.
In order to increase the extinction ratio, it was necessary to increase the stripe width of the quenching laser and increase the interaction area.However, in this case, there was a problem that the current injection to the quench laser had to be increased. Was.

Further, in the case of using polarized light, since light for controlling passes through to the output side, a polarizer must be provided on the output side, and there is a disadvantage that the system becomes large.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned problems, and in the fields of optical communication and optical information processing, a light having a large extinction ratio, low power consumption, and laser oscillation controllable. It is to provide a logic element.

(Means for Solving the Problems) The optical logic element of the present invention has an active layer having a superlattice structure in which different kinds of semiconductors are alternately stacked, and the active region has a bent striped superlattice structure. A waveguide formed of a semiconductor crystal, and a cladding region adjacent to the active region in a plane including the active region, a TM-polarized light is incident from an input end of a semiconductor laser made of a semiconductor crystal in which the superlattice is mixed. In this way, the oscillation of the TE polarized light is interrupted.

(Operation) According to the present invention, by using the superlattice structure and the mixed crystal of the superlattice, only the TE polarized light is guided to the stripe-shaped waveguide layer forming the active layer of the semiconductor laser, and the TM Polarized light may not be guided. Due to this property and the non-linear stripe shape, the TM-polarized light is made incident on the laser oscillating with the TE-polarized light as control light, the laser oscillation is stopped, and the TM-polarized light as the control light is not emitted from the emission end face. It is possible to

Further, the interaction region between the laser light and the control light is formed along the waveguide, and thus becomes large. Therefore, the power of the control light for stopping the laser oscillation may be small. Further, since a superlattice is used as the active region of the laser, the oscillation threshold current of the laser is low.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a perspective view showing a configuration of a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a substrate, for example, n-type Ga.
Consists of an As substrate. 2 is an n-type lower cladding layer,
Al _x Ga _1-x As (eg, x
= 0.3), and Si is converted to 10 ¹⁸ /
It is mixed at a concentration of about cm ³ . Reference numeral 3 denotes an active layer of the semiconductor laser, which is GaAs, Al _y Ga _1-y As (for example, y = 0.
3) It is composed of a superlattice layer having a repeating structure of a thin layer of about 80 ° Reference numeral 4 denotes a partially mixed superlattice obtained by partially mixing a superlattice having the same structure as that of the active layer by a method described later. 5 is p
Upper cladding layer of the mold, wherein Al _x Ga _1-x As (for example, z
= 0.3), and Be is 10 ¹⁸ / cm 3 to be a p-type semiconductor.
It is mixed at a concentration of about ³ . Reference numeral 6 denotes a cap layer made of GaAs. Reference numeral 7 denotes a p-type ohmic electrode. On the back side of the substrate, an n-type ohmic electrode 8 is formed.

Next, a method for manufacturing a semiconductor laser having the above configuration will be described.

First, an n-type cladding layer 2 is formed on a substrate 1 by using a crystallographic method such as molecular beam epitaxy (MBE) or metal organic chemical vapor deposition (MOCVD) that can control the film thickness at an atomic level.
μm, the superlattice layer 3 which becomes the active layer and the lateral cladding layer is 0.6 μm, the upper cladding layer 5 is 1.5 μm,
The cap layer 6 is epitaxially grown by 0.2 μm.

 The following process is performed on the grown wafer.

First, SiO ₂ is deposited on the entire surface of the wafer to a thickness of about 2000 ° by a plasma CVD method or the like. Thereafter, only the upper part of the S-shaped laser region is removed by a photolithography technique and reactive ion etching (RIE). The width of the laser region is 5 μm. Next, in a state where the superlattice patterned with SiO ₂ and another GaAs wafer are stacked, a heat treatment is performed in a hydrogen atmosphere under the conditions of a heating rate of 30 ° C./sec, a heat treatment temperature of 950 ° C., and a heat treatment time of 30 sec. By this heat treatment, S
The superlattice under the iO ₂ film is partially mixed and becomes a partially mixed superlattice, forming a cladding layer in the lateral direction of the active layer.

Next, SiO ₂ is removed by RIE or the like, and the substrate is thinned to about 80 μm. Thereafter, as shown in FIG. 1, a p-type ohmic electrode 7 is deposited on the upper part of the S-shaped laser region, and finally an n-type ohmic electrode 8 is deposited on the back surface of the substrate 1,
Cleavage completes the fabrication.

By the above process, the band gap becomes larger in the region partially mixed with SiO ₂ as compared with the superlattice portion, and the refractive index is increased as shown in FIG. 2 (a). As the degree increases, the birefringence decreases. As for the TE-polarized light, the partially mixed crystal region has a smaller refractive index than the laser active region, as shown in FIG. In the region, only TE polarized light can be guided.

 Next, the operation of the laser will be described.

In the active layer having a superlattice structure, the gain of TE polarized light is larger than that of TM polarized light, and the reflectance at the cleavage plane of the crystal constituting the mirror of the resonator is larger in TE polarized light than in TM polarized light. Because of the fact that only TE polarized light is guided by the waveguide structure described above, laser oscillation
Occurs with TE polarized light. When TM polarized light is incident on the waveguide in the laser active region, the TM light stimulates population inversion in the active region and causes stimulated emission.

As a result, the TM light is amplified, and the oscillation of the TE light stops due to a decrease in gain. Since the amplified TM light does not guide the waveguide, it diffuses into the semiconductor substrate. As shown in FIG. 3 (a), since the laser stripe is not straight but S-shaped, the diffused TM light almost completely escapes from inside the waveguide. Therefore, when observing the output light at the emission end of the waveguide forming the active layer region of the laser, the TE oscillation light turns off and on with the on and off of the incident TM light, and the off state of the TE light In this case, light hardly passes through the emission end. The state of the output light described above is shown in FIG. Output light power on / off ratio (extinction ratio) is 20dB
It was about.

Embodiment 2 FIG. 4 shows the operation of the second embodiment of the present invention. Second
This embodiment differs from the first embodiment in that a coat (AR coat) for reducing the reflectance is applied to the incident end of the TM light. The reflectivity of the AR coat is set to such a level that the laser oscillates. The coating reduces reflection at the end face of the waveguide when the TM light is incident, so that light can be effectively incident into the waveguide. Therefore, the on / off ratio (extinction of TE oscillation light) of the TE oscillation light is low. Ratio) can be increased,
It was more than 25dB.

In this embodiment, an example of a GaAs / AlGaAs system has been described.
Needless to say, it can be applied to other semiconductor materials such as aAsP / InP and InGaAs / InAlAs.

(Effects of the Invention) As described above, according to the present invention, a superlattice structure in which different kinds of semiconductors are alternately stacked, a mixed crystal of a superlattice containing no impurities, and an S-shaped waveguide structure are used. do it,
It is possible to turn on / off laser oscillation with low power consumption control light. In addition, since the control light does not enter the waveguide, the extinction ratio (the power ratio at the time of on / off) is also 20
dB level can be achieved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing the configuration of the first embodiment of the present invention, FIG. 2 (a) is a diagram showing the dependence of birefringence on mixed crystal, and FIG. 2 (b) is refraction for TE polarized light. FIG. 3 (a) is a diagram showing the operation of the first embodiment, FIG. 3 (b) is a diagram showing the optical output of the first embodiment, and FIG. FIG. 5 is a diagram showing the operation of the second embodiment, and FIG. 5 is an explanatory diagram of a logical operation using a conventional laser for oscillation and a laser for extinction. 1 ...... substrate _{2 ...... n-Al x Ga 1} -x As cladding layer 3 ...... superlattice active layer, 4 ...... partially disordered superlattice _{5 ...... p-Al z Ga 1} -z As cladding layer 6 GaAs cap layer, 7 p-ohmic electrode 8 n-ohmic electrode 9 main laser, 10 quenching laser

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 6/12 H01S 3/18

Claims (1)

(57) [Claims] 1. A waveguide comprising an active layer having a superlattice structure in which different kinds of semiconductors are alternately stacked, and a semiconductor crystal having the superlattice structure in the form of a bent active region. In a semiconductor laser made of a semiconductor crystal in which the superlattice is mixed in a plane including the active region in a plane including the semiconductor region, the oscillation of the TE polarization is interrupted by inputting the TM polarization from the input end of the semiconductor laser. An optical logic element, comprising: