JPS63179317A - Spatial light modulator - Google Patents

Abstract

PURPOSE:To permit sufficient light intensity modulation with a low voltage by forming a CCD to a prescribed channel thickness and changing a coefft. of optical absorption by the electric field generated via a transfer electrode. CONSTITUTION:The thickness of the GaAs channel 12 of an undoped MQW layer on a semi-insulating GaAs substrate 11 forming the CCD is determined at the thickness smaller than do Broglie wavelength of electron. The voltage dependency of the change in the coefft. of optical absorption in the thickness direction of the channel 12 corresponding to the electric field generated by the opaque electrode 13 for charge transfer, the voltage impressed to the semi- transparent electrode and the transfer charge is thereby increased. As a result, the intensity of the light which is incident from above and emerges downward is sufficiently modulated with the low voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a spatial light modulator required for image processing, optical computers, and the like.

(Prior art and its problems) A spatial light modulator spatially modulates the intensity and phase of incident light, and is an essential key device when constructing a parallel optical information processing system. Figure 3 shows a conventional example of a spatial light modulator using a buried channel type "S coupling device (hereinafter abbreviated as CCD)", which is published in Applied Physics Letters (^pp1. Phys, Lett.
41.1982>, pages 413-415. In the figure, 31 is a semi-insulating GaAs substrate, 32 is n-type GaAs, 33 is an opaque electrode, and 34 is a semi-transparent electrode. When a voltage is applied to the electrode, Franz
- The optical absorption coefficient of n-type GaAs 32 changes in the layer thickness direction due to the Keldysh effect.

If charges are accumulated under the semi-transparent electrode 34, even if the voltage is constant, the effective electric field strength in the layer thickness direction changes, making it possible to spatially modulate the intensity of the incident light.

The problem with this element is that the absorption coefficient has little voltage dependence, and sufficient intensity modulation cannot be achieved unless a high voltage is applied to the electrodes. For example, with an applied voltage of about 5μ, the channel thickness is 2.5μm and the carrier concentration is 5×101! With IQ11-3, intensity modulation of only about 5% was possible in the absence of charge.

The present invention has been made in view of the above-mentioned drawbacks, and an object of the present invention is to provide a spatial light modulator capable of sufficiently varying the intensity with low voltage.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the spatial light modulator provided by the present invention consists of a charge-coupled device, and the channel has a thickness of about the de Broglie wavelength of electrons or less. It is formed by laminating semiconductor thin films on a substrate, and the electric field generated by the voltage applied to the transfer electrode and the transferred charges changes the optical absorption coefficient in the layer thickness direction, and this change causes the incident light to have a spatial effect. It is characterized in that it emits light with an intensity variation]j.

(For f'r-) The change in the absorption coefficient α(ω) due to the Franz-Ke Idysh effect of a bulk semiconductor is expressed as (1). In equation (1), ω and ωg are angular frequencies corresponding to the incident light and the forbidden V width, respectively, and R is a constant. In addition, θF is expressed as θp = (e2F2/
2mr ``hr) 1/3'''' (2) By increasing the electric field, the absorption coefficient of light on the longer wavelength side with respect to the forbidden band increases.

For thin film semiconductors thin enough to produce quantum effects, Fran
It is possible to increase the e+dysh effect on Z-.

Figure 2 shows the AρG a As / G a As system consisting of a double hetero (DH) @crystal and a multiple quantum well (M Q
W) This is the result of measuring the electric field dependence of the absorption coefficient with the crystal. In the same figure, α0 is the absorption coefficient at F=O, and Eg is the forbidden band energy.9For example! The absorption coefficient for light on the +OleV long wavelength side is 2.6 times when F = 3.3X 104 V/piece, and F = 5. exio't V/ci
Te4. : 1.9 times photo-MQW can be made larger than DH6 Therefore, by using a thin film semiconductor with a small thickness that allows quantum effects to appear for the CCD channel, spatial intensity modulation can be performed at a low voltage. becomes possible.

(Example) FIG. 1 is a sectional view showing an embodiment of the present invention.

In the figure, 11 is a semi-insulating GaAs substrate;
2 is undoped MQW7I! So, the layer thickness is 115 people.
Same as AsW121 <115 people ff1JIV A A
xGap-, Ash (x=0.35) 122 are formed by alternately repeating 110 rounds.

The M thickness of the channel is approximately 2.511y+. MQW layer 1
The carrier concentration of 2 is n = 5 x 1015an-'
It is. 13 is an opaque electrode for charge transfer made of Schottky-type Ti-Au, and 14 is a semi-transparent electrode using semi-transparent 'ri'.

In order to avoid the influence of absorption loss in the substrate 17,
As shown in FIG. 1, the edges are formed by etching. Electrode opening/closing is 24 times, and charge transfer is performed by three clock oscillators. F=! in Figure 2! 1.6X 10'V/a
In this case, the electric field corresponding to i is approximately 5 V in terms of voltage, and with this structure, the change is 2 to 3 times larger than in the conventional example, and the extinction ratio is also 3 dB to 5 dB higher. It became possible to do this.

(Effects of the Invention) As explained above, in the spatial light modulator of the present invention, since the voltage change in the optical absorption coefficient in the layer thickness direction is large, the degree of modulation is high, and sufficient intensity modulation can be achieved with a low voltage. It is.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the electric field dependence of the absorption coefficient in a semiconductor crystal, and FIG.
The figure is a cross-sectional view of a conventional example. 611 and 31 are semi-insulating G
a A s substrate, 12 is MQW scrap, 12 is GaA
s, II, 122 is A jJ z Cr a 1-
xA s M, 32 is n-type GaAs, 13 and 33 are opaque electrodes, and 14 and 34 are semitransparent electrodes.

Claims (1)

[Claims] In a charge-coupled device, a channel is formed by laminating a semiconductor thin film on a substrate with a thickness of about the de Broglie wavelength of electrons or less, and the channel is formed by stacking a semiconductor thin film on a substrate with a thickness equal to or less than the de Broglie wavelength of electrons. A spatial light modulator characterized by changing the optical absorption coefficient in the thickness direction, and using the change to spatially modulate the intensity of incident light and emit the same.