Device for switching from one light source to another

• US 4,720,162 A
• Filed: 04/11/1986
• Issued: 01/19/1988
• Est. Priority Date: 05/11/1981
• Status: Expired due to Term

• Current Assignee: KDD Submarine Cable Systems Inc.
• Original Assignee: Kokusai Densin Denwa Kabushiki Kaisha
• Inventors: Wakabayashi, Hiroharu, Tokiwa, Hideharu, Namihira, Yoshihori, Mochizuki, Kiyofumi
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Ullah, Akm E.
• Application Number:
  US06/850,453
• Time in Patent Office: 648 Days
• Field of Search: 350/96.15, 350/96.16, 350/96.18, 350/96.19, 350/360, 350/370
• US Class Current: 385/16
• CPC Class Codes: G02B 6/2713 cascade of polarisation selective or adjusting operations
• CPC Class Codes: G02B 6/274 based on light guide birefringence, e.g. due to coupling between light guides G02B6/105, G02B6/024 take precedence; mechanically induced birefringence G02F1/0134
• CPC Class Codes: G02B 6/2773 Polarisation splitting or combining
• CPC Class Codes: G02B 6/4215 the intermediate optical elements being wavelength selective optical elements, e.g. variable wavelength optical modules or wavelength lockers G02B6/4246 takes precedence

Abstract

An optical coupler is formed of at least one polarization maintaining single mode fiber, a polarizing beam splitter connected to the polarization maintaining single mode fiber, and a main optical fiber which is connected with the polarizing beam splitter at one end thereof. This optical coupler is useful as a changeover switch for a light source.

Claims

1. A light switching device for switching from one light source to another, comprising first and second light sources for emitting linear polarized light waves;

first and second polarization maintaining single mode fibers each having an input end disposed adjacent a respective one of said light sources so that light beams output from said light sources enter into said fibers respectively, said fibers being so disposed relative to said light sources that the polarization axis of each of said fibers is substantially parallel to the polarization axis of the light waves incident on said fiber from its associated light source;

a main track optical fiber for propagating said light beams output from both of said light sources; and

a polarizing beam splitter disposed between the output ends of said first and second polarization maintaining single mode fibers and the input end of said main track optical fiber;

said first and second polarization maintaining single mode fibers being operative to transmitting said light beams with the planes of polarization of said light beams being respectively maintained and with horizontal polarized light waves P and vertical polarized light waves S crossed perpendicularly to each other being emitted from the output ends of said optical fibers;

said polarizing beam splitter having four planes the planes of incidence of which differ from the planes of emission thereof in dependence on the planes of polarization of the light beams that are output from said optical fibers;

said polarization maintaining single mode fibers being so oriented to the respective planes of said polarizing beam splitter that some of the horizontal polarized light waves P and vertical polarized light waves S output from said optical fibers emerge simultaneously from the same plane of said polarizing beam splitter as emission light, one of said light sources being normally used as an ON operating light source and the other of said light sources being normally used as an OFF standby light source; and

means responsive to the magnitude of said emission light from said same plane for controlling the ON-OFF states of said operating and standby light sources.

2. The light switching device of claim 1 wherein lenses for collecting light are disposed between the output ends of said polarization maintaining single mode fibers and said polarizing beam splitter as well as between said polarizing beam splitter and the input end of said main track optical fiber.

3. The light switching device of claim 1 wherein a λ

/4 wave plate is disposed between said polarizing beam splitter and said main track optical fiber for preventing reflected light returning through said main track optical fiber from entering said operating light source.

4. The light switching device of claim 1 wherein the polarizations of said first and second light sources are oriented in the same direction, at least one of said first and second polarization maintaining single mode fibers that transmit the light beams emitted from said light sources being so twisted that the axes of polarization at the output ends of said fibers are at an angle of 90°

to one another.

5. The light switching device of claim 1 wherein the planes of polarization of light emitted by said first and second light sources are disposed at an angle of 90°

to one another, said first and second polarization maintaining single mode fibers transmitting the light beams emitted from said light sources being so arranged that the light beams input to said fibers are led to the light output ends of said fibers while maintaining the planes of polarization of said input light beams.

6. A light switching device for switching from one light source to another, comprising a polarizing beam splitter provided with four end faces A, B, C and D;

first, second, third and fourth optical fibers coupled respectively to said end faces A, B, C and D, said polarizing beam splitter being operative to issue through said end face D both a polarizing wave P which is fed into said beam splitter through said end face A and a polarizing wave S which is fed into said beam splitter through said end face B;

said first optical fiber being a polarization maintaining single mode fiber having one end thereof optically coupled to said end face A of said polarizing beam splitter with the axis of polarization of said one end of said first fiber being deviated from the polarizing axis of said polarizing beam splitter at an angle sufficient to leak a detectable amount of light via said beam splitter from said first optical fiber to said end face C, and said second optical fiber also being a polarization maintaining single mode fiber having one end thereof optically coupled to said end face B of said polarizing beam splitter with the axis of polarization of said one end of said second fiber being deviated from the polarizing axis of said polarizing beam splitter at an angle sufficient to leak a detectable amount of light via said beam splitter from said second optical fiber to said end face C;

a first light source operative to generate polarizing light P, said first light source being connected to a second end of said first polarization maintaining single mode fiber at a location remote from end face A of said polarizing beam splitter, a second light source operative to generate polarizing light S, said second light source being connected to a second end of said second polarization maintaining single mode fiber at a location remote from end face B of said polarizing beam splitter; and

switching means responsive to the turning on of either selected one of said first and second light sources for turning off the other of said light sources without the slightest interruption, said switching means including said third optical fiber having one end thereof optically coupled to said end face C of said polarizing beam splitter for transmitting the said detectable amount of the polarizing light P and polarizing light S from the one of said first and second light sources respectively that is turned on thereby to monitor the operation of the said one of said first and second light sources that is turned on;

said fourth optical fiber having one end thereof optically coupled to the end face D of said polarizing beam splitter for transmitting output light via said beam splitter from the one of said first and second light sources that is turned on.

7. The light switching device of claim 6 wherein at least one lens is inserted between each of said polarization maintaining single mode fibers and the polarizing beam splitter.

8. The light switching device of claim 6 or claim 7 wherein one of said first and second light sources is an operating light source and the other of said light sources is a standby light source.