Optical fiber coupler

• US 4,750,795 A
• Filed: 06/13/1985
• Issued: 06/14/1988
• Est. Priority Date: 06/13/1985
• Status: Expired due to Fees

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Blotekjaer, Kjell
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Ullah, Akm E.
• Application Number:
  US06/744,502
• Time in Patent Office: 1,097 Days
• Field of Search: 350/96.15, 350/96.16, 350/96.18, 350/96.29, 455/612
• US Class Current: 385/24
• CPC Class Codes: G02B 6/2817 using reflective elements to split or combine optical signals
• CPC Class Codes: G02B 6/2821 using lateral coupling between contiguous fibres to split or combine optical signals

Abstract

A fiber optic coupler comprises a multimode fiber bus, an input branch fiber, and an output branch fiber. Coupling between the fibers is accomplished by means of a reflector, disposed in the core of the multimode optical fiber. The reflector is quite small, such that only a small fraction of the light propagating in the multimode fiber is incident thereon. The incident light is reflected towards the output branch fiber and coupled thereto through a lens. Light propagating in the input branch fiber towards the multimode fiber is focused on the reflector by means of a lens. The reflector is oriented to reflect the focused light in a generally cone-shaped beam directed longitudinally down the axis of a multimode fiber. Preferably, the cone-shaped beam diverges so that substantially all the modes within the acceptance cone of the multimode fiber are excited. Such excitation of the modes is preferably equalized by selecting the numerical aperture of the multimode fiber such that only the portion of the reflected beam which has a relatively uniform intensity is within the acceptance cone of the fiber. The invention is particularly advantageous for local area networks and distributed sensor systems.

Claims

1. A fiber optic coupler, comprising:

a first optical fiber;

a second multimode optical fiber, said multimode fiber including plural mode groups; and

a reflector, substantially smaller than the core of said multimode optical fiber, said reflector disposed within the core of said multimode optical fiber and positioned to receive light from said first optical fiber and reflect the light for propagation in said second multimode optical fiber, said multimode fiber having a total reflection complementary angle, said reflector and said total reflection complementary angle of said multimode fiber being relatively sized to cause substantially all of said plural mode groups to be excited with said reflected light, said reflected light being distributed among said plural mode groups of said multimode fiber substantially in proportion to the number of modes in each of said mode groups.

2. A fiber optic coupler, as defined by claim 1, wherein said first optical fiber is a single mode optical fiber which propagates light in a generally Gaussian shaped energy distribution and wherein said reflector is sized to receive only that portion of light propagating in said first fiber which is within the peak of said energy distribution such that said reflector is substantially uniformly illuminated.

3. A fiber optic coupler, comprising:

a first optical fiber;

a second multimode optical fiber, said multimode fiber including plural mode groups; and

a reflector, substantially smaller than the core of said multimode optical fiber, said reflector being substantially disk-shaped, and having reflective surfaces on both sides thereof, said disk-shaped reflector disposed within the core of said multimode optical fiber and positioned to receive light from said first optical fiber and reflect the light for propagation in said second multimode optical fiber, said multimode fiber having a total reflection complementary angle, said disk-shaped reflector and said total reflection complementary angle of said multimode fiber being relatively sized to cause substantially all of said plural mode groups to be excited with the reflected light.

4. A fiber optic coupler, comprising:

a first optical fiber;

a second optical fiber, said second fiber being multimode and having plural mode groups; and

means for coupling optical power from said first fiber to said second fiber, said coupling means distributing said optical power among substantially all of said plural mode groups, substantially in proportion to the number of modes in each of said mode groups.

5. A fiber optic coupling system, comprising:

a multimode bus fiber;

plural reflectors disposed within the core of said multimode bus fiber at locations which are spaced at intervals along said fiber; and

a series of branch fibers, each disposed at one of said spaced interval locations, said reflectors positioned to receive light from said branch fibers, respectively, and reflect said light for propagation is said multimode fiber to provide optical communication between said bus fiber and said branch fibers at said locations, the diameter of said reflectors selected in accordance with the radius of the core of said multimode fiber and the total number of reflectors within said core to maximize the transmission of optical power from the first of said series of branch fibers to the output of said bus fiber.

6. A fiber optic data coupling system, as defined by claim 5, wherein said branch fibers are optically connected to respective sensors.

7. A fiber optic coupling system, comprising:

a multimode bus fiber;

plural reflectors disposed within the core of said multimode bus fiber at locations which are spaced at intervals along said fiber; and

a series of branch fibers, each disposed at one of said spaced interval locations, said reflectors positioned to receive light from said branch fibers, respectively, and reflect said light for propagation in said multimode fiber to provide optical communication between said bus fiber and said branch fibers at said locations, the diameter of said reflectors selected in accordance with the radius (a) of the core of said multimode fiber and the total number of reflectors (n-1) within said core to maximize the transmission of optical power from the first of said series of branch fibers to the output of said bus fiber, said diameter (d) of said reflectors being approximately equal to;

##EQU12##

8. A fiber optic coupling system, comprising:

a multimode bus fiber;

plural reflectors disposed within the core of said multimode bus fiber at locations which are spaced at intervals along said fiber;

a first series of branch fibers, each disposed at one of said spaced interval locations, said reflectors positioned to receive light from said first series of branch fibers, respectively, said reflectors including respective surfaces for reflecting said light from said first series of branch fibers for propagation in said multimode fiber to provide optical communication between said bus fiber and said first series of branch fibers at said locations, the diameter of said reflectors selected in accordance with the radius of the core of said multimode fiber and the total number of reflectors within said core to maximize the transmission of optical power from the first of said series of branch fibers to the output of said bus fiber; and

a second series of branch fibers, each disposed at one of said locations, said reflectors further including respective surfaces for reflecting light from said multimode fiber to said second branch fibers, respectively.

9. A method of manufacturing a fiber optic coupling system comprising the steps of:

providing a multimode bus fiber having plural reflectors within the core of said bus fiber at locations which are spaced at intervals along said fiber;

positioning a sereis of branch fibers, each disposed at one of said locations, such that said reflectors receive light from said branch fibers, respectively, and reflect said light for propagation in said multimode fiber to provide optical communication between said branch fibers and said bus fiber at said locations; and

sizing the diameter of said reflectors as a function of the core radius of said multimode fiber and the total number of reflectors within said core to maximize the transmission of optical power from the first of said series of branch fibers to the output of said bus fiber.