JPH01287627A - Light switching method - Google Patents

Abstract

PURPOSE:To switch light rays at high speed with a simple element structure by modulating the transmission intensity of modulated signal light by changing the absorption coefficient of the wavelength of the signal light by irradiating signal light by control light having a shorter wavelength than the signal light has, to control intensity of light with another light. CONSTITUTION:The transmission intensity of signal light irradiated by control light having a wavelength shorter than that of the signal light in a state where a DC electric field is impressed upon a quantum well structure is modulated to control the intensity of transmitted signal light. Namely, the DC electric field impressed upon the quantum well structure is compensated by performing screening by means of carriers produced by optical excitation and light switching is performed by light by utilizing a change in absorption coefficient. Therefore, high-speed light switching is made possible with a simple element structure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical switching method that can be used in optical communications and optical information processing.

BACKGROUND OF THE INVENTION In recent years, various devices have been proposed and prototyped that modulate transmitted light and reflected light by irradiating a quantum well structure with light and applying a modulating electric field to the quantum well structure. A conventional transmissive optical modulator will be described below with reference to the drawings. FIG. 5 shows a diagram of the principle of the optical modulator.

A quantum well structure is created in one layer of the p-i-n structure, and an electric field is applied to the quantum well. The quantum well structure is p
The sum of the built-in voltage of the -i-n structure and the externally applied voltage is applied. The absorption coefficient spectra of the quantum well structure when the electric field E applied to the quantum well structure is zero and when E)O are shown by solid lines and broken lines in FIG. The two peaks in each spectrum correspond to the absorption edge of the 1S exciton transition (1hh1e) that accompanies the transition from the first quantum level of holes to the first quantum level of electrons, where the longer wavelength side is heavier,
The 1S exciton transition (fji!
It corresponds to the absorption edge of h-16). When an electric field is applied to the quantum well structure, each absorption edge shifts to the longer wavelength side due to the quantum confined Stark effect. Now, as shown in Figure 2, 1
The quantum well structure is irradiated with signal light having a wavelength λS longer than the absorption edge of the hh16 transition. The absorption coefficient at wavelength λS is α1. If α0, α1
>α0, the transmittance of the signal light is lowered by applying an electric field. That is, the transmitted light is switched by modulating the absorption coefficient by electric field modulation.

Problems to be Solved by the Invention However, in the above configuration, when driving serially using an optical signal, the control light must be converted into an electrical signal once. For this purpose, a converting section and the like are required, which makes the element structure complicated.

Also, the operating speed is slow because it is converted into an electrical signal once.

Means for Solving the Problem In order to solve this problem, the optical switching method of the present invention uses a signal light that is irradiated with a DC electric field applied to a quantum well structure to have a wavelength shorter than that of the signal light. The control light beam is irradiated with control light, the transmitted intensity is modulated, and the transmitted signal light intensity is controlled.

Effect: With this configuration, the DC electric field applied to the quantum well structure is screened with carriers generated by photoexcitation to cancel the DC electric field, and the resulting change in absorption coefficient can be used to switch light.

Embodiment In the present invention, the control light is used to directly modulate the signal light using the screening effect without converting the control light into an electrical signal. This will be explained below using figures. FIG. 1 shows a diagram of the principle of the present invention. The present invention differs greatly from conventional technology in that (1) the electric field applied to the quantum well structure is only a DC electric field and does not require a muC electric field component, and (2) it is light-light direct modulation. be.

In addition, the same point as the conventional technology is that the well surface of the quantum well structure is vertically irradiated with signal light having a wavelength λS set on the longer wavelength side than the absorption edge of the 1hh1e exciton transition, and the amount of transmitted light changes. Alternatively, a waveguide may be formed with a quantum well structure to guide signal light having a wavelength λS, and changes in the amount of transmitted light may be utilized. Here, as a method of changing the transmittance of the quantum well structure, that is, the absorption coefficient at the wavelength λS, the following method is used.

(2) First, one layer of the p-i-n structure is made into a quantum well structure, and an electric field is applied to the quantum well structure by applying a reverse voltage to the p-i-n structure.

Absorption spectra in a state in which no electric field is applied to the quantum well structure and in a state in which an electric field is applied are shown by solid lines and broken lines in FIG. When an electric field is applied to the quantum well structure, the absorption edge shifts to the longer wavelength side due to the quantum-confined Stark effect.

In this state, the absorption coefficient at the wavelength λS is larger than the absorption coefficient when no electric field is applied, so the transmitted light intensity is in a weak state. (Figure 2 broken line OFF state)
■1 hh 1 when no electric field is applied there
When the quantum well structure is irradiated with a control light having a wavelength λC set to a wavelength corresponding to the absorption edge of the e-exciton transition,
Carriers excited by the control light having wavelength λC cancel the electric field applied to the quantum well structure by a screening effect. Moreover, when the electric field is canceled out, the absorption edge shifts to the short wavelength side, so the absorption coefficient at wavelength λG increases and positive feedback is added. Furthermore, carriers are generated in the quantum well, so the electric field suddenly becomes zero. Become,
The absorption coefficient at wavelength λS becomes small. Therefore, the transmitted light intensity becomes strong.

(FIG. 2 solid line ON state) The extra carriers generated at this time flow as photocurrent. (2) When the irradiation of the control light λG is stopped, the state immediately returns to (2) due to the applied electric field.

By repeating the states (1), (2), and (2) as described above, light can be switched.

That is, it can be seen that when the control light is ON, the signal light is also in the ON state, and when the control light is OFF, the signal light is also in the OFF state.

However, the intensity and irradiation time of the control light must be such that it excites a sufficient density of carriers to screen the electric field. In general, the areal density of the carrier N
s is a carrier density greater than or equal to Ns=εSεOE/6 (εS: relative dielectric constant of the quantum well structure, C0: dielectric constant of vacuum, Σ: electric field applied to the quantum well structure, e: charge amount of electrons).

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows an example of a waveguide type used in the present invention.

In FIG. 3, 1 is an n-GaAs substrate (carrier density N ~ 10 cm, thickness t ~ 200 μm), 2
is an n-GaAg buffer layer (N ~ 5 × 10
Cm, t: ~0.1 μTB), 3 is n-
Person 7! x Gal −X As (X = 0.5)
Cladding layer (N ~5 x 10"C111-3, t=
1 μm), Jt.

i -MQW guide layer (GaAs well layer 100 people and 1x Ga, -x As (X = 0.5)
Barrier layer 100 people, 20 cycles, N ~ 10 cm
, t==4000 people), 6 is P-mulz Ga+-
2As (X ~ 0.5) ri7)'i (N
~5X10 cllll, t ~1 μm),
6 is a P-GaAs cap layer (N ~ 1019 cm
', t=1 pm), 7 is Ti/muU.

8 is an AuGeNi/Au ohmic contact.

Length L of the waveguide: 100 μrn @w = 2 μm.

Furthermore, anti-reflection coatings are applied to both end faces of the input and output sides of the signal light.

In order to apply an electric field to the quantum well structure, a voltage of 3V is applied in the opposite direction to the p-i-n junction, and at this time, in addition to the built-in voltage (~27), ~5v is applied.

Since the thickness of the i-layer is 400 mm, each quantum well has ~
An electric field of 1.2 X I Q5V /crn is applied.

In addition, the signal light has a wavelength of 858 nm and a power density of 10 W/
- TK waves are incident on the waveguide from one direction as shown in FIG. When an electric field is applied as described above, the wavelength is 11348 nm, the power density is 1 KN, /al! I
, TE wave control light is irradiated from the side of the waveguide, and the fifth
Width 1 n560. Repetition period 4ns
When switching was performed using EC, the output light was the 6th
The response was as shown in the figure.

The ON10 FF ratio of the output light was ~3, and the loss when ON was ~30.

Similar effects were also obtained in a combination in which signal light and control light were irradiated perpendicularly to the quantum well surface.

In addition, in the present invention, the same effect was obtained in any combination of the quantum well structure in the example with 50 to 200 well layers, a barrier layer width of 6 Å or more, and 1 to 6 wells. Moreover, the operating wavelength is not limited to around 850 nm as shown in this example, but can be changed from 680 nm to 880 nm by selecting the molar ratio of Mul in the well layer and the applied electric field!
A similar effect was obtained in the GaAjJAs-based quantum well structure.

The switching device of the present invention can also be applied to materials other than AlG51G5, such as rnGaAsP and InGaA4P.

Incidentally, in the above embodiment, a similar effect was obtained even in a structure in which all the conductivity types were reversed.

Effects of the Invention According to the present invention, an optical signal can be directly switched using another optical signal for control. Therefore, high-speed switching is possible with a simple element structure, and the effect is significant when considering applications such as optical ICs.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the present invention in detail, Figure 2 is a diagram for explaining the quantum confined Stark effect of the absorption coefficient spectrum of a quantum well structure, and Figure 3 is a diagram for explaining the invention in detail. FIG. 4 is a diagram showing the response characteristics of the control light and output light of the present invention, and FIG. 6 is a diagram showing the principle of a conventional optical switching element. 1...n-GaAS substrate, 2...n
-GaAs buffer layer, 3...n-Mupa AAS cladding layer, 4...i -MQW guide layer, 5...P-I GaAs cladding layer , 6... P-GaAs cap layer, 7...
...Ti/muU electrode, 8...muGeNi
/Au IE pole. Name of agent: Patent attorney Toshio Nakao and one other person
sect

Claims (1)

[Claims] In a quantum well structure made by alternately stacking semiconductor materials with different bandgaps, 1S excitons are generated that accompany the transition from the first quantum well level of heavy holes to the first quantum well level of electrons in the quantum well structure. The modulated signal is irradiated with signal light having a wavelength longer than the wavelength corresponding to the absorption edge of the transition, and a DC electric field is applied to the quantum well structure in a direction perpendicular to the well surface. A light characterized in that by irradiating control light with a shorter wavelength than the light, the absorption coefficient at the wavelength of the signal light is changed, the transmission intensity of the signal light is modulated, and the intensity of the light is controlled by the light. Switching method.