JP2717210B2 - Semiconductor optical waveguide polarization element - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor optical waveguide type polarizing element having polarization plane selectivity applicable to optical communication and optical signal processing.

(Prior Art) Conventionally, there is a metal cladding polarizer as this type of waveguide type polarizing element. This metal cladding polarizer has the characteristic that it absorbs the TM mode and transmits only the TM mode by cladding the metal directly on the optical waveguide surface.

As this conventional example, a literature (Y. Suematsu, M. Hakuta, K.
Appl.Phys, Let by Furuya, K. Chiba, and R. Hasumi
t., vol. 21, No. 6, pp. 291-293, Sept. 1972). Such a conventional example will be described with reference to FIG.

FIG. 4 is a configuration diagram of a conventional example. A thin film 12 having a larger refractive index is provided on a substrate 11 to serve as an optical waveguide layer. Thin film
A metal (aluminum) film 13 is provided on a part of 12. The light is propagated by the prism 14 in the order of A → B → C → D. While propagating between the BCs, only the TM mode is attenuated, and from the D, only the TE mode is emitted.

(Problems to be Solved by the Invention) In the conventional example as shown in FIG. 4, only the TE mode can be transmitted, but either the TE or TM polarization mode cannot be selectively transmitted. Also, the optical waveguide layer
12 has only one-dimensional optical confinement, and the light is
Since it spreads while propagating through 12, the intensity of the signal light is attenuated. Therefore, the conventional example cannot be applied as a waveguide type element for the purpose of optical signal processing or the like.

When performing optical signal processing using a waveguide-type element, the waveguide-type element often operates only for either TE or TM polarized light, and therefore, it is often necessary to select either TE or TM mode. Required. The present invention has been proposed in order to meet the above demand, and provides a semiconductor optical waveguide type polarizing element that selectively removes either TE mode or TM mode and selectively transmits only one polarization mode. The purpose is to:

(Means for Solving the Problems) In order to achieve the above object, the present invention is configured such that one semiconductor optical waveguide having two-dimensional optical confinement is branched into two, and then made one again. A plurality of interferometric light intensity modulators to be connected in tandem, a semiconductor optical waveguide type polarizing element,
It consists of an optical waveguide formed on a zinc-blend type semiconductor crystal having a symmetry of 3 m, and two or more interferometric light intensity modulators connected in tandem are the optical waveguides constituting the interferometric light intensity modulator. The direction is <0 in the (100) plane of the semiconductor.
A first interference type light intensity modulator parallel to the 1> direction or the <011> direction, and a second interference type in which an angle between the first interference type light intensity modulator and the first interference type light intensity modulator is 45 degrees. The semiconductor optical waveguide constituting the first interference type optical intensity modulator, which is distinguished from the optical intensity modulator, is located in the (100) plane and is <01.
> Extends in the direction parallel to the direction, and through the electrode (100)
An electric field perpendicular to the plane is applied, and the second interferometric light intensity modulator section is such that the optical waveguide is in the (100) plane and is 45 degrees with the optical waveguide of the first interferometric light intensity modulator section. By applying an electric field through an electrode in a direction parallel to the (100) plane and perpendicular to the direction in which the optical waveguide extends, the first
Wherein only the TE mode is modulated in the interferometric light intensity modulator portion and only the TM mode is modulated in the second interferometric light intensity modulator portion so that either one can be selectively emitted. It is an object of the present invention to provide a type polarizing element.

Therefore, in order to effectively perform optical signal processing using the waveguide element, the present invention most prefers to selectively transmit only one of the TE and TM polarization modes by applying a voltage. Main features. In the conventional waveguide polarizer, the polarization mode to be transmitted is predetermined,
It was impossible to selectively transmit only an arbitrary polarization mode. On the other hand, the present invention is significantly different from the prior art in that a polarization mode that transmits by applying a voltage can be selected. Further, the metal cladding polarizer of the prior art has only one-dimensional light confinement, and is difficult to apply to an optical waveguide device. On the other hand, the polarizing element of the present invention is composed of a semiconductor optical waveguide having two-dimensional optical confinement, and is sufficiently applicable to an optical integrated circuit as an optical waveguide element.

(Operation) Since the present invention is configured by cascade-connecting two interferometric light intensity modulators each formed by a semiconductor optical waveguide having two-dimensional optical confinement, the TE or TM is changed depending on the voltage applied to the electrodes. Either polarization mode can be selectively transmitted.

Next, examples of the present invention will be described. It should be noted that the embodiments are merely examples, and it is needless to say that various changes or improvements can be made without departing from the spirit of the present invention.

(Embodiment) FIG. 1 shows an embodiment of a semiconductor optical waveguide type variable light device according to the present invention. In this figure, signal light propagates in a semiconductor optical waveguide having two-dimensional optical confinement in the order of A → B → C → D → E → F. The square PQRS is the (100) plane of a zinc-blend semiconductor crystal with a symmetry of 3 m, such as GaAs or InP. PQ and PS are cleavage planes perpendicular to <011>.
And SP are cleavage planes perpendicular to <01>. 1a, 1b and 2a, 2b represent electrodes provided on both sides of the optical waveguide, respectively.

A first interference type optical intensity modulator is formed between B and C, after one optical waveguide is branched into two linear optical waveguides and then returned to one. The length of the optical waveguide between the BCs is the same regardless of the path. The straight line composed of A, B and C is parallel to PQ, that is, a straight line in the <01> direction. Between the DEs is the same second interferometric light intensity modulator as between the BCs. The first and second interferometric light intensity modulators between BC and DE are smoothly connected via an optical waveguide CD so as to form an angle θ with each other. The optical waveguide EF forms a smooth curve for emitting signal light from the cleavage plane QR parallel to the SP. Reference numerals 1a and 1b denote electrodes of the first interferometric light intensity modulator, and 2a and 2b denote electrodes of the second interferometric light intensity modulator.

2 and 3 are cross-sectional views of the interferometric light intensity modulator between BC (first) and DE (second) along KL and MN, respectively. 2 and 3, 4 is a semiconductor substrate having a (100) plane, 6 is a film epitaxially grown on the semiconductor substrate 4, and 5 is formed in the epitaxial film 6 and has a larger refraction than the film 6. It is a semiconductor optical waveguide having an index. 7, 9 and 10 are high carrier concentration regions for obtaining an ohmic junction with the electrode 8 or 11, respectively.
The region 7 applies a voltage to the optical waveguide 5 in a direction perpendicular to the (100) plane, and the regions 9 and 10 apply a voltage to the optical waveguide 5 in a direction parallel to the (100) plane. 3, 8 and 11 are ohmic electrodes.

 Next, the operation will be described.

It is assumed from FIG. 1A that elliptically polarized light in which a TE mode whose polarization direction is parallel to the (100) plane and a TM mode whose polarization direction is perpendicular to the (100) plane are mixed. A voltage is applied to one of the two parallel optical waveguides constituting the first interferometric light intensity modulator between BCs in the direction perpendicular to the (100) plane via the electrodes 3 and 8 in FIG. Is applied, the phase of only the TE mode of the TE mode and the TM mode propagating in the optical waveguide can be changed. At this time, the phase of the TM mode does not change at all. By appropriately selecting the voltage to be applied, the phase change amount of the TE mode can be set to a half wavelength, that is, π.
The TE mode has a phase opposite to that of the TE mode propagating in the other optical waveguide of the first interferometric light intensity modulator at C.
The subsequent light intensity of the TE mode propagating through the optical waveguide disappears. Then, the first and second interferometric light intensity modulators between BC and DE are manufactured so that the angle θ is ± 45 degrees.
In the embodiment shown in the figure, one of the two parallel optical waveguides constituting the second interferometric light intensity modulator between DEs is provided with one of the electrodes 11 of FIG. 3 in a direction parallel to the (100) plane. When a voltage is applied through the optical waveguide, the phase of only the TM mode of the TE mode and the TM mode propagating in the optical waveguide can be changed.

By appropriately selecting the voltage to be applied, the phase change amount of the TE mode can be set to π, and the relationship of the E mode and the TM mode which has propagated through the other optical waveguide can be reversed.
Therefore, the light intensity of the TM mode propagating through the optical waveguide after E disappears. In this case, the propagation light of the TE mode does not undergo any phase change between DMs.

2 having modulation characteristics for such TE and TM modes
In the embodiment of FIG. 1 in which two interferometric light intensity modulators are connected in cascade, a signal light in which TE and TM modes coexist is input from A, and one optical waveguide of the interferometric light intensity modulator between BC is input. When an appropriate voltage is applied to the light source and no voltage is applied to the interferometric light intensity modulator between DEs, F can output only the TM mode. Further, when a voltage is not applied to the interferometric light intensity modulator between BC and an appropriate voltage is applied to one of the optical waveguides of the interferometric light intensity modulator between DE, F to TE
Only the mode can be output.

As is clear from this result, the polarizing element of the present invention in which two interferometric light intensity modulators each formed by a semiconductor optical waveguide having two-dimensional light confinement are connected in cascade, TE or TE depends on the voltage applied to the electrode. It has the feature that any polarization mode can be selectively transmitted.

(Effects of the Invention) As described above, the semiconductor polarization element according to the present invention can select the polarization mode to be transmitted by applying a voltage and is constituted by an optical waveguide having two-dimensional optical confinement. This has the effect that it can be applied as an optical waveguide device for optical signal processing.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a semiconductor optical waveguide type polarizing element of the present invention,
2 and 3 are sectional views taken along lines KL and MN in FIG. 1, and FIG. 4 shows a conventional example. 1a, 1b, 2a, 2b: Modulating electrodes 3, 8, 11: Electrode 4: Semiconductor substrate 5: Optical waveguide 6: Epitaxially grown film having a smaller refractive index than optical waveguide 5 7, 9, 10 ... High carrier concentration region

Claims (1)

(57) [Claims] 1. An interferometric light intensity modulator comprising a semiconductor optical waveguide having two-dimensional optical confinement, which is divided into two, and then split into two. A semiconductor optical waveguide type polarizing element to be connected, the semiconductor optical waveguide type polarizing element comprises an optical waveguide formed on a zinc blend type semiconductor crystal having a symmetry of 3 m,
In the two or more interferometric light intensity modulators connected in cascade, the direction of the optical waveguide forming the interferometric light intensity modulator is <01> orientation or <011> orientation in the (100) plane of the semiconductor. A first interferometric light intensity modulator parallel to
The semiconductor optical waveguide constituting the first interferometric light intensity modulator is distinguished from the second interferometric light intensity modulator in which the angle formed by the interferometric light intensity modulator is 45 degrees. ,(Ten
0) an electric field which extends in a direction parallel to the <011> direction in the plane, applies an electric field perpendicular to the (100) plane through an electrode, and the second interferometric light intensity modulator comprises an optical waveguide Is (10
0) A direction extending in the plane at an angle of 45 degrees with the optical waveguide of the first interferometric light intensity modulator, parallel to the (100) plane and perpendicular to the direction in which the optical waveguide extends. The first interferometric light intensity modulator modulates only the TE mode and the second interferometric light intensity modulator modulates only the TM mode by applying an electric field through the electrodes to select either one. A semiconductor optical waveguide type polarizing element characterized in that light can be emitted to the substrate.