US 5,689,597 A · Multimode interference couplers and method therefor

Abstract

The invention relates to the field of integrated optics and communication techniques. In these fields, integrated, compact passive beam splitters and combiners are of great importance. These optical functions can be fulfilled by means of multimode interference (MMI) couplers. A given number of inputs is evenly distributed to all outputs. These components have wide manufacturing tolerances and are substantially independent of polarization. In the conventional MMI couplers with parallel sides, the intensity and phase distribution at the output are fixed. However, since in many applications, these distributions must be influenced in a controlled manner, the invention provides a method of changing the intensity and phase distributions at the outputs of MMI couplers in a controlled manner. The conventional MMI couplers are first split up into sections. Each section is then separately transformed so that the self-imaging properties are maintained. At the end, the sections are arranged in series again. By appropriate choice of the transformations, different controlled beam splitters and combiners can be obtained. The distributions are changed by means of a simple, tolerant control of geometrical parameters.

Claims33

Dependent claims

A multimode interference (MMI) coupler having an input face and an output face, which coupler comprises at least two sections which are arranged in the direction of propagation and jointly constitute an unsplit multimode waveguide, wherein at least one of said two sections constitutes an MMI coupler having a geometry which differs from that of a conventional MMI coupler, so that a resultant phase distribution which differs from that of the conventional MMI coupler occurs at an end face of said first section, said phase distribution producing a desired interference phenomenon at the output face.

A method of changing the intensity and phase distribution at an output face of a precursor multimode interference (MMI) coupler having parallel lateral sides so as to produce a modified MMI coupler, the method comprising the steps of:

splitting the precursor MMI coupler into first and second conventional MMI coupler sections in the direction of propagation, each of said first and second sections having a start face and an end face, the end face of said second MMI coupler section constituting an output face of said modified MMI coupler;
and
transforming at least one of said first and said second conventional MMI coupler sections in such a way as to produce a modified MMI coupler section having a phase distribution at its end face which differs from that of the phase distribution at the end face of the precursor MMI coupler section, and which phase distribution changes the interference phenomenon at the output face of the precursor MMI coupler into a selected interference phenomenon at the output face of the modified MMI coupler.

An improved multimode interference (MMI) coupler having an input face and an output face, which MMI coupler comprises first and second MMI coupler sections proximate to one another in the direction of propagation, wherein said first and second MMI coupler sections define an unsplit multimode waveguide, the improvement characterized in that at least said first MMI coupler section constitutes a modified MMI coupler having a geometry which differs from that of a precursor MMI coupler, so that a resultant phase distribution which differs from that of the precursor MMI coupler occurs at an end face of said first section, said phase distribution producing a selected interference phenomenon at the output face, wherein the precursor MMI coupler is characterized as having a length L in the direction of propagation defined as

L=(M/N)*(3/A)*L.sub.c
wherein
L.sub.c =.pi./(.beta..sub.0 -.beta..sub.1).apprxeq.4nW.sup.2 /3.lambda.
and wherein
A is a real number,
.beta..sub.0 and .beta..sub.1 are respective propagation constants of first and second modes of the precursor MMI coupler,
W is the width of the precursor MMI coupler,
n is the index in the precursor MMI coupler,
.lambda. is the wavelength in vacuum,
N is the number of images, and
M is an integer, where N and M do not have a common sub-multiple.

8 more elements

Dependencies are inferred from the claim text.

Multimode interference couplers and method therefor

Life of this patent

Multimode interference couplers and method therefor

Life of this patent

Abstract

Claims33