OPTICAL MODULATORS

• US 3,748,597 A
• Filed: 10/28/1971
• Issued: 07/24/1973
• Est. Priority Date: 10/28/1971
• Status: Expired due to Term

• Current Assignee: Franz Karl Reinhart
• Original Assignee: Franz Karl Reinhart
• Inventors: Reinhart, Franz Karl
• Primary Examiner(s): Borchelt, Benjamin A.
• Assistant Examiner(s): Moskowitz, N.
• Application Number:
  US05/193,286
• Time in Patent Office: 635 Days
• Field of Search: 332/7.51 350/150,161 250/199
• US Class Current: 359/279
• CPC Class Codes: G02F 1/0154 using electro-optic effects, e.g. linear electro optic [LEO], Pockels, quadratic electro optical [QEO] or Kerr effect
• CPC Class Codes: G02F 1/0157 using electro-absorption effects, e.g. Franz-Keldysh [FK] effect or quantum confined stark effect [QCSE]
• CPC Class Codes: G02F 1/025 in an optical waveguide structure G02F1/017, G02F1/2257 take precedence
• CPC Class Codes: G02F 2203/07 Polarisation dependent
• CPC Class Codes: H01S 5/20 Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
• CPC Class Codes: H01S 5/2059 by means of particular conductivity zones, e.g. obtained by particle bombardment or diffusion
• CPC Class Codes: Y10S 148/065 Gp III-V generic compounds-processing
• CPC Class Codes: Y10S 148/067 Graded energy gap
• CPC Class Codes: Y10S 148/107 Melt

Abstract

An optical phase modulator comprises a semiconductive body having first, second and thrid layers, the second layer being contiguous with and intermediate to the first and third layers and being of a material having a bandgap and free carrier concentration lower than that of both of the first and third layers. Optical radiation to be modulated is transmitted through the second layer across which is applied an electric field to effect the modulation. In a preferred embodiment the body and the field are mutually adapted so that a depletion layer is created coextensive with the second layer. Under this condition, the phase modulation per unit power and bandwidth achieves a relative maximum for the fundamental transverse mode. Structures which employ a p-n junction, as well as ones which do not, are disclosed. Optical polarization and intensity modulators are also described.

Claims

1. In a device for modulating optical radiation in response to an electric field, a multilayered semiconductor body comprising first, second and third semiconductor layers, said second layer being a high resistivity layer contiguous with an intermediate to said first and third layers and having a bandgap and free carrier concentration lower than that of both said first and third layers, said second layer being adapted for the transmission of said radiation therethrough and being responsive to said electric field applied to said body for modulating said radiation so that said field is substantially concentrated in said second layer.

2. The body of claim 1 wherein said first and third layers are of the same conductivity type and said second layer is intrinsic.

3. The body of claim 1 wherein said first and third layers are of opposite conductivity type and said second layer is intrinsic.

4. The body of claim 1 wherein said first and third layers are of the same conductivity type and said second layer is compensated.

5. The body of claim 1 wherein said first and third layers are of opposite conductivity type and said second layer is compensated.

6. The body of claim 1 wherein said first and third layers are of opposite conductivity type and said second layer comprises contiguous Nu and pi -type regions defining a junction therebetween, said electric field being applied to said second layer in a reverse bias connection.

7. The body of claim 1 wherein said first, second and third layers comprise respectively AlxGa1 xR, AlyGa1 yR and AlzGa1 zR, where 0 <

or = y <

x and z and R is an element selected from the group consisting of As and P.

8. The body of claim 7 wherein the free carrier concentration in said second layer is less than or equal to approximately 1017/cm3.

9. The body of claim 1 wherein said electric field includes a d.c. bias field which extablishes a depletion layer in said second layer and wherein the amplitude of said bais field and the relative carrier concentrations in said layers are mutually adapted so that said depletion layer is substantially coextensive with said second layer.

10. The body of claim 1 wherein a portion of each of said layers is etched away to form a mesa-like configuration of the remaining portions of said layers.

11. The body of claim 1 wherein a portion of each of said layers is bombarded with protons to form a mesa-like structure of the remaining portions of said layers.

12. The body of claim 1 including a pair of electrical contacts across which said field is applied, at least one of said contacts having a stripe geometry so that the temperature of a first region of said second layer immediately beneath said stripe contact is higher than that of other regions of said second layer laterally displaced from said first region and contiguous therewith, thereby to cause the index of refraction in said first region to be greater than that in said other regions.

13. A device for modulating the intensity of optical radiation propagating along a transmission path comprising a polarizer and an analyzer disposed in said path in sapced relation to one another, and a semiconductor body according to claim 1 disposed in said path between said analyzer and said polarizer so that said second layer is positioned to receive said radiation for transmission therethrough, said polarizer being oriented to linearly polarize said radiation at approximately 45* to two of the principal axes of the refractive index ellipsoids of said second layer, said body being adapted to produce half wave phase retardation of said polarized radiation.

14. The body of claim 1 wherein said second layer is characterized by a band edge at a characteristic energy and wherein the wavelength of said radiation corresponds to an energy below and near to said band edge, said electric field being effective to shift said band edge in accordance with the amplitude of said field thereby to alter the optical absorption in said second layer and to intensity modualte said radiation.

15. A unitary device comprising a double heterostructure injection laser having a pair of wide bandgap layers of opposite conductivity type, a narrower bandgap active region layer disposed between said pair of layers, and at least one partially transmissive surface normal to said active region, and a semiconductor body according to claim 1 having at least one surface normal to said second layer contiguous with and electrically insulated from at least one of said partially transmissive surfaces of said laser, said second layer of said body being coplanar with and optically coupled to said active region layer of said laser.

16. An optical modualtor comprising a heat sink, a multilayered semiconductor body mounted on said heat sink and comprising a semiconductor substrate, a plurality of semiconductor layers epitaxially grown on said substrate in the following order:

an AlxGa1 xAs layer, x >

0, an AlyGa1 yAs layer 0 <

or = y <

x, an AlxGa1 zAs layer, z >

0 and y<

z, and a GaAs layer, a pair of electrical contacts, one formed on said substrate and one on said GaAs layer, the free carrier concentration of said AlyGa1 yAs layer being lower than that of both said AlxGa1 xAs and AlzGa1 zAs layers and being less than or equal to approximately 1017/cm2, means for applying a d.c. electric field across said contacts so that a depletion layer is established coextensive with said second layer, and an information source connected across said contacts for applying to said body an a.c. electric field which varies in amplitude in accordance with information to be transmitted, said second layer being adapted for the transmission of said radiation therethrough, the refractive index of said second layer being responsive to changes in the amplitude of said a.c. electric field for phase modulating said radiation, said field being substantially concentrated in said second layer.