JPH01204019A - Optical modulator - Google Patents

Abstract

PURPOSE:To obtain the optical modulator which can be increased in on-off ratio while the loss in its on state is small by using an optical control layer which has specific multiple quantum well structure. CONSTITUTION:The optical modulator is provided with the optical control layer 14 of multiple quantum well structure formed by laminating a 1st barrier layer 141 consisting of a 1st semiconductor, a 1st well layer 142 consisting of a 2nd semiconductor layer which has larger forbidden band width than the 1st semiconductor layer, a 2nd barrier layer 143 consisting of a 3rd semiconductor which has a smaller forbidden band width than the 2nd semiconductor, a 3rd barrier layer 145 consisting of a 3rd semiconductor, a 3rd well layer 146 consisting of a 2nd semiconductor, and a 4th barrier layer 147 consisting of the 1st semiconductor in order. Consequently, an active layer which decreases in the absorption when an electric field is applied is used, so the optical modulator which is increased in waveguide length, small in on-state loss, and large in the on-off ratio is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical logic element used for optical information processing and the like, and in particular to an optical modulator.

[Conventional technology]

In recent years, digital information processing that takes advantage of the high speed of light has attracted attention. This requires the development of logic elements that control light. One of them is an optical modulator that electrically turns on and off optical signals.

Conventionally, the structure shown in FIG. 3 as an optical modulator is called Electronics Letters.
rs) Vol. 21, p. 693, (1985) by Wood (T. H.) et al.

This optical modulator has quantum well layers 31 that are made of thin films of GaAs and GaAlAs that are alternately laminated with conductivity types of p-type and n-type, respectively.
It has a pin structure sandwiched between cladding layers 32 and 33 made of GaAlAs. In the figure, 11 is an n-type InP substrate, 17 is an n-side electrode, and 18 is a p-side electrode. In the optical modulator having such a structure, light incident from one end face passes through the quantum well layer 31 and exits from the other end face. Application of an electric field reduces the effective bandgap, so switching is performed by taking advantage of the fact that the absorption coefficient of excitons in the quantum well for light on the low energy side increases.

[Problem to be solved by the invention]

The conventional optical modulators described above utilize changes in the absorption coefficient of quantum wells for light, but the absorption coefficient on the low energy side is relatively large even when no electric field is applied, so the output in the off state is If the length of the waveguide is increased in order to reduce

An object of the present invention is to provide an optical modulator with low loss in the on state (and a high on/off ratio).

[Means to solve the problem]

The optical modulator in the present invention includes a first optical modulator made of a first semiconductor.
a first well layer made of a second semiconductor having a smaller bandgap than the first semiconductor; a second barrier made of a third semiconductor having a larger bandgap than the second semiconductor. a second well layer made of a fourth semiconductor having a smaller band gap than the second semiconductor, a third barrier layer made of the third semiconductor, and a third well made of the second semiconductor. The optical control layer is characterized by having a multi-quantum well structure in which a fourth barrier layer made of the first semiconductor is sequentially laminated as a light control layer.

[For production]

The energy band diagram of the multi-quantum well structure serving as the active layer in the present invention is shown in FIG. FIG. 2(a) shows the case when no electric field is applied, and FIG. 2(b) shows the case when the electric field is applied. In the figure, 21 is the potential for electrons, 22 is the potential for holes, 23 is the envelope of the electron wave function, and 24 is the envelope of the hole wave function. Further, 141 is a first barrier layer, 142 is a first well layer, 143 is a second barrier layer, 14
4 is a second well layer, 145 is a third barrier layer, 146 is a third well layer, and 147 is a fourth barrier layer.

In the active layer, electrons and holes are confined in the second well layer 144. When no electric field is applied, the wave functions of electrons and holes overlap greatly, and the oscillator strength of excitons is also large. In this state, the transmittance is in an off state due to large absorption by the active layer.

When an electric field is applied, the wave function of electrons seeps into the third well layer 146 as shown in FIG. 2(b), but the wave function of holes remains in the second well layer 144, so they overlap each other. becomes smaller. Therefore, the oscillator strength of the exciton decreases, and the absorption coefficient decreases. Due to the decrease in absorption by the active layer, the light transmittance increases rapidly, resulting in an on state.

The present invention uses a multi-quantum well structure in the active layer that has low absorption when an electric field is applied, so even if the length of the waveguide is increased, the loss in the on state is small and the on-off ratio is low. A large optical modulator can be realized.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention.

This optical modulator is manufactured as follows. That is, a substrate 11 of n-type InP is doped with Si and has a thickness of 0.
．． n-cladding layer 13 of 1 μm thick InP doped with a contact layer 12.3i of 5 μm InP;
, a first barrier layer 141 . made of non-doped InP with a thickness of 20 nm. Non-doped I n (1,1s
A first well F) 1142 made of Gao, 5sASo, tqPo, g+, and a second barrier layer 143 made of non-doped InP with a thickness of 3 mm. 5mm thick non-doped I
n 00S3G ao, 4? A second well layer 144 made of AS, and a third barrier layer 145 made of non-doped InP with a thickness of 3 mm. 10nm thick non-doped In0.6S
G a 6,15 A s O,? 9pH,! Third well layer 146 made of I, non-doped InP with a thickness of 20 nm
a light control layer 14 having a multi-quantum well structure in which a fourth barrier layer 147 is sequentially stacked 101i each; a p-cladding layer 15 made of Mg-doped InP with a thickness of 1 μm;
Furthermore, p-1nGa with a thickness of 0.1 μm doped with Zn
AsP contact layers 16 are sequentially laminated to form an n-side electrode 17.
and p-side electrode 18 are formed, respectively. InGaAs
P has a composition with a band gap of 0.95 eV.

Leaving the waveguide portion 100 with a width of 10 μm and the electrode pad 110 with a diameter of 100 μm, the other portions are etched and removed up to the substrate 11. The length of the waveguide is 200 μm.

When the voltage between the n-side electrode 17 and the p-side electrode 18 is 12V,
The spatial overlap between electrons and holes is small, and the oscillator strength of excitons in the multiple quantum well structure of the light control layer 14 is also small. For example, the magnitude of the absorption coefficient for light of 0.954 eV is 12 cm-I.

The insertion loss at this time is 1 dB. When the voltage is reduced, the spatial overlap of electrons and holes increases, so the absorption coefficient of the multi-quantum well structure of the light control 7114 increases and the transmittance decreases.

〔Effect of the invention〕

As described in detail above, according to the present invention, an optical modulator with low loss in the on state and a large on/off ratio can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a schematic diagram showing the energy band of the multiple quantum well structure of the light control layer in the present invention, and FIG. 3 is an example of a conventional optical modulator. FIG. 11...Substrate 12...Contact layer 13...Clad layer 14...Light control layer 141...First barrier layer 142...First well layer 143... Second barrier layer 144... Second well layer 145... Third barrier layer 146... Third well layer 147... Fourth barrier layer 15... Cladding layer 16... ... Contact layer 17 ... N-side electrode 18 ... P-side electrode agent Patent attorney Yoshiyuki Iwasa

Claims (1)

[Claims] (1) A first barrier layer made of a first semiconductor, a first well layer made of a second semiconductor with a smaller forbidden band width than the first semiconductor, and a first well layer made of a second semiconductor with a smaller forbidden band width than the second semiconductor. a second barrier layer made of a large third semiconductor; a second well layer made of a fourth semiconductor with a smaller forbidden band width than the second semiconductor; a third barrier layer made of the third semiconductor; An optical modulator having, as an optical control layer, a multi-quantum well structure in which a third well layer made of the second semiconductor and a fourth barrier layer made of the first semiconductor are sequentially laminated.