Optical waveguides – Polarization without modulation
Patent
1997-02-04
1998-12-08
Ngo, Hung N.
Optical waveguides
Polarization without modulation
385 43, 385 33, G02B 626
Patent
active
058482032
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to an optical isolator, in an optical system employing a semi-conductor laser, wherein the isolator prevents reflected or returned light from entering into the emitter of the optical system. Applications of such a system include fiber-optic communication, reading to and writing from optical discs, etc.
BACKGROUND ART
Polarization-independent optical isolators employing a semiconductor laser are often used for interrupting reflection-returned light in optical systems such as optical fiber communication systems and optical disc input/output devices. In particular, a polarization-independent optical isolator must be attached to a optical fiber amplifier to prevent fluctuations in its outputs. The polarization-independent optical isolator using a polarization beam splitter functions in such a way that optical paths for respective polarized components having their polarized directions orthogonal to each other are separated or coupled (JP-B 60-49297, JP-B 61-58808, etc.).
FIG. 5 is a schematic view for showing a polarization-independent optical isolator using wedge type polarization beam splitters as proposed in JP-B 61-58809. A first lens 27A opposes an end face of a light-emitting side optical fiber 26A, whereas a second lens 27B opposes an end face of a light-incident side optical fiber 26B. Arranged between the first lens 27A and the second lens 27B are a first wedge type polarization beam splitter 28, a Farady rotator 29 and a second wedge type polarization beam splitter 30 in this order.
Two polarized components being orthogonal to each other are emitted from the light-emitting side optical fiber 26A, and pass through first lens 27A. As the polarized components pass the first wedge type polarization beam splitter 28, they undergo different refractions depending upon their polarizations, so that they are separated into two beams 31A and 31B. The polarization planes of the separated polarized components 31A and 31B are turned by the Farady rotator 29, and the polarized components are converted into parallel beams through their angular changes by means of the second wedge type polarization beam splitter 30. At this time, the polarized components emitted from the second wedge type polarization beam splitter 30 have the same orientation, but they are positionally deviated. This parallel light is focused into the light-incident side optical fiber 26B by the second lens 27B.
On the other hand, reflected light propagating in a backward direction is shown by dotted lines. Polarized components constituting the return light and being orthogonal to each other are binarily divided by the second wedge type polarization beam splitter 30, and the polarization plane of each of the polarized components separated is turned by the Farady rotator 29 in the same direction as the forward direction. As a result, the polarization direction in which the polarized component passes the first wedge type polarization beam splitter 28 differs from that in the case of the forward propagation by 90.degree.. Consequently, the polarization components deviate positionally and angularly from each other, different from the light beams in the forward propagation. After the polarized components pass the first lens 27A, they become the parallel beams, but their optical axes are positionally deviated from that of the optical fiber 26A, so that the parallel beams are not coupled with the light-emitting side optical fiber.
FIG. 6 is a schematic view for showing a polarization-independent optical isolator using parallel-faced flat plate type polarization beam splitter as proposed in JP-B 60-49297. A first lens 27A is opposed to an end face of a light-emitting side optical fiber 26A, whereas a second lens 27B opposes an end face of a light-incident side optical fiber 26B. Arranged between the lens 27A and the lens 27B are a first parallel-faced flat plate type polarization beam splitter 32, a Farady rotator 33, and second and third parallel-faced flat plate type polarization beam splitters 29, 3
REFERENCES:
patent: 5588078 (1996-12-01), Cheng et al.
patent: 5642448 (1997-06-01), Pan et al.
K. Shiraishi, Y. Aizawa, S. Kawakami; "Beam Expanding Fiber Using Thermal Diffusion of the Dopant"; IEEE Journal of Lightwave Technology; Aug. 1990; vol. 8, pp. 1151-1161.
Kawakami Shojiro
Shimo Masashi
Shiraishi Kazuo
Kawakami Shojiro
Ngo Hung N.
Shiraishi Kazuo
Sumitomo Osaka Cement Co. Ltd.
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