Optical waveguides – Optical fiber waveguide with cladding – Utilizing multiple core or cladding
Reexamination Certificate
1998-07-20
2001-04-24
Bovernick, Rodney (Department: 2874)
Optical waveguides
Optical fiber waveguide with cladding
Utilizing multiple core or cladding
C385S126000, C385S128000
Reexamination Certificate
active
06222972
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical fiber favorable for middle-range and short-range, light information-transmitting materials. More precisely, it relates to a wide-band plastic-clad optical fiber favorable for light information-transmitting materials for constructing LAN (local area networks) such as high-speed and large-capacity data links for middle-range and short-range networks, and the like.
BACKGROUND ART
Step-index-type plastic-clad optical fibers (hereinafter referred to as PCF) comprising a quartz core and a plastic clad are relatively inexpensive, and, when compared with plastic optical fibers of which the core and the clad are both made of plastics, have higher light transmittance and better bondability to light-emitting and light-receiving devices and are easier to handle. For their such characteristics, PCF are much used as optical fibers for middle-range and short-range light information transmission and those in light guides.
For example, PCF described in Japanese Patent Application Laid-Open (JP-A) Hei-5-271350, of which the core is made of pure quartz and the clad is of UV-cured fluorine resin, is usable as a light information-transmitting material for intra-system communication, inter-system communication, mobile communication, intra-building communication and the like. As its clad is made of fluorine resin having high hardness, the PCF is compatible with crimp-style connectors, and field working of the PCF including connector application thereto is easy.
However, though having such excellent handlability, workability, connector applicability and bondability and being inexpensive, those conventional PCF have a large numerical aperture (NA) of from 0.37 to 0.40 and therefore their transmission band is narrow. Accordingly, for light information-transmitting materials for wide-band information transmission systems of ATM-LAN (Asynchronous Transfer Mode-LAN), high-speed Ethernet and the like, the conventional PCF are unsatisfactory as their transmission band is too narrow.
On the other hand, graded-index-type and single-mode-type optical fibers of quartz, which are known as materials for high-speed information transmission, have a wide transmission band, but require troublesome working and connector application and even complicated material designing and clad constitution. Therefore, their production costs are difficult to reduce.
Given that situation, the object of the present invention is to improve PCF which are easy to work, to which connector application is easy and for which material designing and clad constitution is easy, to thereby broaden their band with no disadvantages including contact loss for simple crimp-style connectors, bending loss and even light transmittance loss in temperature change.
DISCLOSURE OF THE INVENTION
The invention provides a plastic-clad optical fiber comprising a quartz core and a polymer clad tightly formed around the core, in which the clad has a multi-layered structure of a plurality of different polymers, and the refractive index of the core (n
CO
), that of the first clad tightly formed around the core (n
CL1
) and that of the second clad formed over the first clad (n
CL2
) satisfy both 0.21≦(n
CO
2
−n
CL1
2
)≦0.35 and n
CL2
<n
CL1
.
To realize wide-band plastic-clad optical fibers (PCF), it is necessary to lower the numerical aperture (NA=(n
CO
2
−n
CL
2
) of the fibers. For this, in the PCF of the invention, the refractive index of the first clad (n
CL1
) and that of the core (n
CO
) shall satisfy 0.21≦(n
CO
2
−n
CL1
2
)≦0.35.
For favorably using optical fibers in wide-band information transmission systems, their band for a transmission distance of from 100 to 200 m must be at least 156 Mbps. Conventional step-index-type PCF could hardly satisfy such a high band level. If having a reduced numerical aperture (NA) of not more than 0.35, PCF could practically satisfy the band level of at least 156 Mbps (for 100 to 200 m).
However, light passing through the core of a step-index-type optical fiber that has a small numerical aperture is easily in a radiation mode when the fiber is bent. Therefore, as so noted hereinabove, reducing the numerical aperture (NA) of PCF is problematic in that the bending loss is increased to be a great bar to the practical use of PCF. Accordingly, the lowermost limit of the numerical aperture (NA) of PCF having one clad layer is not less than 0.36 in order that the bending loss of the PCF could be on the same level (not higher than 0.35 dB) as that practically allowed for conventional PCF (having a large numerical aperture of from 0.37 to 0.40). The bending loss as referred to herein means the decrease in the quantity of light from the initial light quantity, as measured by applying an LED light source having an incident NA of 0.25 to a 3-meter optical fiber that is wound 10-fold around a mandrel having a radius of 5 mm.
Specifically, the bending characteristic of PCF is influenced not only by the refractive index of the clad that determines the numerical aperture (NA) of PCF but also by the physical properties of the polymer that forms the clad and by the degree of dispersion in the clad coating condition in the lengthwise direction. Therefore, too much reduction in the numerical aperture (NA) of PCF to lower than 0.36 shall have greater negative influences on the bending characteristic of PCF, which is much more influenced by the physical properties of the clad polymer and by the clad coating condition, resulting in that PCF having such a small numerical aperture (NA) could no more have a stable bending characteristic necessary for its practical use.
For these reasons, the lowermost limit of the numerical aperture (NA) of PCF having one clad layer is not less than 0.36 in order that the PCF could have a stable bending characteristic.
However, in PCF, when a second clad, of which the refractive index satisfies n
CL2
<n
CL1
, is formed around the first clad, the increase in the bending loss of PCF could be prevented even if the numerical aperture of the first clad [(n
CO
2
−n
CL1
2
)] is reduced to fall between 0.21 and 0.35. This is because, when the optical fiber is bent, the radiation mode once produced in the interface between the core and the first clad is completely reflected on the interface between the first clad and the second clad and is thereby returned back. As opposed to this, however, when n
CL2
≧n
CL1
, the radiation mode could not be completely reflected on the interface between the first clad and the second clad, resulting in that the radiant light is radiated out of the optical fiber and is lost. In that case, the second clad could not exhibit the function to prevent the increase in the bending loss of the optical fiber.
Reducing the numerical aperture (NA) of PCF to broaden the band thereof is problematic, as increasing the caulking loss when crimp-style connectors are fitted to the outer surface of the clad by caulking. To overcome this problem and to realize practical use of such PCF, the connector caulking loss must be reduced to the same level (not more than 0.5 dB) as that for conventional PCF (having a large numerical aperture of from 0.37 to 0.40). For PCF having one clad layer, however, if they are desired to have a caulking loss of not more than 0.5 dB (at incident NA of 0.20 in full-mode excitation), like conventional PCF, irrespective of the composition and the physical properties of the clad, the degree of dispersion in the clad coating condition in the lengthwise direction and even the type of the crimp-style connectors used, the lowermost limit of the numerical aperture (NA) of those PCF shall be not less than 0.36. If the lowermost limit is less than 0.36, the influences of the composition and the physical properties of the clad and of the degree of dispersion in the clad coating condition in the lengthwise direction on the characteristics of PCF are not negligible, and practical PCF with stable characteristics are difficult to obtain.
However, the multi-layered PCF of the invent
Kobayashi Hisaaki
Taneichi Shoshiro
Yamamoto Tetsuya
Bovernick Rodney
Miller Austin R.
Stahl Michael J.
Toray Industries Inc.
LandOfFree
Wideband plastic-clad optical fiber does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wideband plastic-clad optical fiber, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wideband plastic-clad optical fiber will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2553181