Ferrule product, method of making the same, and optical module

Details Ferrule product, method of making the same, and optical module Ferrule product, method of making the same, and optical module

2002-03-14

2004-10-19

Flech, Karl D. (Department: 2876)

Optical waveguides

With disengagable mechanical connector

Optical fiber to a nonfiber optical device connector

C385S091000, C385S092000

Reexamination Certificate

active

06805492

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ferrule product, a method of making the same, and an optical module.
2. Related Background Art
As the transmission capacity of optical communications increases, wavelength division multiplexing transmission systems (hereinafter referred to as WDM transmission systems) have come in to use. Inconventional WDM transmission systems, those having a channel interval as narrow as about 50 GHz (wavelength interval of 400 pm) have been in practical use. As the light source for such a WDM transmission system, DFB lasers have mainly been in use.
SUMMARY OF THE INVENTION
Further increases in the transmission capacity of optical communications have recently been in demand. For responding to such a demand, WDM transmission systems having a narrower channel interval are necessary. However, the oscillation wavelength of a DFS laser greatly depends on its operating temperature and injection current. Therefore, when a DFB laser is used as a light source, a deterioration in transmission characteristic may occur in adjacent channels due to optical crosstalk. This optical crosstalk occurs, for example, when the oscillation wavelength greatly shifts due to fluctuations in current generated by changes over time during a long-term continuous operation. Since it is necessary for high-density WDM systems to narrow their channel intervals in particular, the occurrence of optical crosstalk may become a serious problem therein. Hence, an external cavity type fiber Bragg grating semiconductor laser constituted by a fiber Bragg grating and a semiconductor optical amplifier has been developed as a light source with further wavelength stability.
As disclosed in a literature (literature 1: M. Ziari, A. Mathur, H. Jeon, I. Booth & R. J. Lang, “FIBER-GRATING BASED DENSE WDM TRANSMITTERS,” NFOEC97, pp. 503-512.), the oscillation wavelength of a fiber Bragg grating semiconductor laser is exclusively determined by the Bragg wavelength of the Bragg grating. Therefore, the temperature dependence of the oscillation wavelength of a fiber Bragg grating semiconductor laser is also determined by the temperature dependence of the Bragg wavelength of the fiber Bragg grating (which is very low, i.e., about 10 pm/K), and its dependence on the injection current to the semiconductor optical amplifier is also very small. Hence, its change in oscillation wavelength with respect to temperature and injection current is remarkably smaller than that in DFB lasers. In addition, when making a fiber Bragg grating, the Bragg wavelength of the fiber Bragg grating can be controlled so as to attain a desirable value more accurately than that of DFB lasers. Therefore, as disclosed in several literatures (literature 2: F. N. Timofeev, P. Bayvel, V. Mikhailov, O. A. Lavrova, R. Wayatt, R. Kashyap, M. Robertson, and J. E. Midwinter, “2.5 Gbit/s directly-modulated fiber grating laser for WDM networks,” Electron. Lett. 1997, pp. 1406-1407.; literature 3: M. Ziari, A. Mathur, H. Jeon, I. Booth & R. J. Lang, “FIBER-GRATING BASED DENSE WDM TRANSMITTERS,” NFOEC97, pp. 503-512.; literature 4: T. Takagi, T. Kato, G. Sasaki, A. Miki, S. Inano, K. Iwai, A. Hamanaka, M. Shigehara, “Fiber-grating external-cavity laser diode imodule for 2.5 Gb/s dense WDM transmission,” Proc. ECOC 1998, pp.81-82.; and literature 5: T. Kato, T. Takagi, A. Hamanaka, K. Iwai, and G. Sasaki, “Fiber-Grating Semiconductor Laser Modules for Dense-WDM Systems,” IEICE TRANS. ELECTRON., VOL. E82-C. No. 2, 1999, pp. 357-359.), fiber Bragg grating semiconductor lasers are remarkably superior to DFB lasers in terms of stability and controllability in wavelength.
As mentioned above, the oscillation wavelength of a fiber Bragg grating semiconductor laser is determined by the Bragg wavelength corresponding to the grating period of its fiber Bragg grating. Therefore, basically the temperature change rate of the oscillation wavelength of a fiber Bragg grating semiconductor laser should be nearly equal to the temperature change rate of the Bragg wavelength of its fiber Bragg grating. Namely, the temperature change rate of the Bragg wavelength of a fiber grating should be about 10 pm/K.
The inventors measured the temperature change rate of the oscillation wavelength of available fiber grating semiconductor lasers. In this measurement, the inventors found that the value of temperature change rate was about 17 pm/K, thus being remarkably greater than the value expected so far.
The inventors carried out various investigations and studies in order to solve the cause of sluch an abnormal value of temperature dependence. As a result, regarding the temperature dependence of oscillation wavelength, the inventors took notice of the structure of a ferrule for holding an optical fiber.
FIG. 13
is a sectional view showing a ferrule product
8
used for technical studies. The ferrule product
8
comprises an optical fiber
81
and a ferrule
82
. The ferrule
82
has a capillary part
821
for holding the optical fiber
81
and a flange part
822
for holding the capillary part
821
.
As a result of various studies concerning the ferrule product
8
, the inventors have found the tollowing fact: The material characteristics and structures of the flange part
822
and capillary part
821
affect the temperature change rate of the Bragg wavelength of the fiber Bragg grating, thereby increasing the temperature change rate of the oscillation wavelength of the fiber Bragg grating laser.
As can be understood from the foregoing explanation, the inventors have found that the oscillation wavelength of fiber Bragg grating semiconductor lasers fails to exhibit its expected stability with respect to temperature. It is unfavorable for the oscillation wavelength to have a large temperature dependence in the case of temperature controlled type fiber Bragg grating semiconductor lasers using a temperature controlling device such as Peltier device, since the burden on temperature control becomes heavier. On the other hand, uncooled fiber Bragg grating semiconductor lasers without temperature controller will be in great demand in access network system if their temperature dependence at present can be significantly reduced. In any case, it is essential that the temperature dependence of oscillation wavelength in fiber Bragg grating semiconductor lasers be lowered so as to achieve the required temperature characteristic.
Therefore, it is an object of the present invention to provide a ferrule product which can reduce the temperature change rate of the Bragg wavelength of fiber Bragg gratings, and a method of making the same; and further to provide an optical module which can reduce the temperature change rate of the oscillation wavelength of a fiber Bragg grating semiconductor laser.
One aspect of the present invention is the ferrule product utilized in an optical module comprising a semiconductor optical amplifier having a pair of end facets. The ferrule product comprises an optical fiber and a ferrule. The optical fiber has one end portion provided so as to be optically coupled with one of the pair of end facets of the semiconductor optical amplifier, a first optical fiber portion including a Bragg grating provided at a predetermined position distanced from the one end portion, and a second optical fiber portion different from the first optical fiber portion. The ferrule has a capillary portion for holding the optical fiber and a flange portion for holding the capillary portion, whereas the flange portion is provided on the second optical fiber portion.
According to this aspect of the present invention, since the flange portion is provided on the second optical fiber portion, the force applied by the flange portion onto the first optical fiber portion of the optical fiber as temperatire rises can be reduced. Therefore, the change in grating period with respect to temperature can be reduced.
In the ferrule product, material of the flange portion may have a coefficient of linear expansion smaller than that of material of the capillary po

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