Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2001-08-31
2003-07-08
Healy, Brian (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S092000, C385S094000
Reexamination Certificate
active
06588948
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module used in optical communications, and more particularly to an optical module, which has high airtightness, and a constant plane of polarization of transmitted light.
2. Description of the Related Art
In the field of optical communications, which has developed phenomenally in recent years, optical module airtightness is seen as being important for the reliable transmission of a light signal. This results from the electrode of an optical semiconductor device arranged on the inside of an optical module deteriorating when, the inside thereof constitutes a high-temperature, high-humidity state, and from the optical properties of an optical semiconductor device deteriorating due to the condensing of moisture that penetrates to the inside, making it impossible to guarantee the life of an optical semiconductor device for more than 10 years.
However, an optical module has the role of using a lens to optically couple an inside optical semiconductor device and an outside optical fiber. To ensure the airtightness of an optical module as-is and maintain the optical system thereof, a, light transmitting-type window structure is employed in an optical semiconductor airtight-sealed housing.
As the window material of the housing (airtight-sealed housing) for an optical module, sapphire is often utilized due to its excellent translucence and high strength. Japanese Patent Application Laid-open No. H8-148594 discloses a basic structure and manufacturing method of a housing for an optical module, which uses sapphire in a light transmitting-type window. Regarding to the window structure of the housing thereof, Japanese Patent Application Laid-open No. H8-148594 discusses the relationship between the optical axis and the C axis of the sapphire. Here, a window structure is proposed, in which an optical axis, which refracts according to Snell's law, is made coincident with the C axis of the window plate, so that occurrence of light birefringence, that is, rotation of the plane of polarization of light is prohibited.
In Japanese Patent Application Laid-open No. H11-54642, an optical module window structure, which uses borosilicate glass as the window plate, is proposed. Borosilicate glass is inexpensive, and its translucency surpasses even that of sapphire. Furthermore, borosilicate glass is an isotropic material, and does not cause the birefringence of light. However, the problem with borosilicate glass is that the plane of linear polarization of transmitted light deforms, namely the plane is not maintained as-is and the light changes into ellipsoidal polarization in some cases, due to the elastic strain resulting from heat stress. But as disclosed in Japanese Patent Laid-open No. 11-54642, it has become clear that the deformation of the plane of polarization of light can be minimized by applying a stress uniformly to the glass, at which time the polarized light extinction ratio described below, which serves as an index of the deformation of the plane of polarization of light, decreases to around −40 dB, and does not pose a problem from the standpoint of practical use.
Here, the deformation of the plane of polarization of light is generally expressed as a polarized light extinction ratio such as the following. In a crossed Nicol prism experimental system, when the polarizer of the light-emitting side was made to rotate 90 degrees relative to that of the light-receiving side, if the maximum light intensity in the light-receiving side is labeled I
max
, and the minimum light intensity is labeled I
min
, then the polarized light extinction ratio is defined as 10×log
10
(I
min
/I
max
). Therefore, this indicates that the smaller the polarized light extinction ratio is, the smaller the deformation of the plane of polarization of light becomes.
In line with the recent advances in technology for increasing transmission speeds and high-density wavelength-multiplexing technology in optical communications, maintaining the constant plane of polarization of transmitted light and ensuring the uniformity of the wavelength thereof have become important tasks. To solve for the latter of these, it is desirable to form an external resonator structure, such as an optical fiber grating, via an optical fiber on the outside of an airtight-sealed housing, but maintaining the constant plane of polarization of light is required in this case as well. The level of plane of polarization maintenance required at this time is the above-mentioned polarized light extinction ratio of −30 dB, that is, a level at which I
max
is 1000-times greater than I
min
, making this a stringent condition incapable of being achieved with the above-mentioned conventional technology.
Furthermore, in the above-mentioned conventional technology, which uses sapphire as the window plate, a method such as the following had to be utilized to achieve the desired relationship between an optical axis and the C axis of sapphire. That is, it was necessary either to use a sapphire plate, which had been cut perpendicular to the C axis, and to make the C axis correspond to the optical axis by arranging the sapphire plate thereof perpendicular to the optical axis, or, when that was not the case, to go to the trouble of grinding and manufacturing a sapphire plate, having a specified angle relative to the C axis, and furthermore, aligning the C axis position of the sapphire plate thereof exactly with the optical axis. In the case of the former, reflected light directly returns to the incoming side, making it unsuitable for an optical module. In the case of the latter, exact alignment was difficult, and it was impossible to manufacture a window part by accurately fixing the angle.
Further, even when borosilicate glass is used as the window plate, borosilicate glass has the drawback of having weak strength. Therefore, a borosilicate glass window plate was not suitable for use under harsher conditions, and was an unsatisfactory material for practical use. In fact, the current situation is such that the use of borosilicate glass is still being shunned in fields in which ultra-high reliability is required for undersea cables.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an optical module having a window structure, which is easy to manufacture, has mechanical strength, and has a small polarized light extinction ratio, holding the plane of linear polarization constant.
According to the present invention, there is provided an optical module comprising:
a housing; and
a junction having a light transmissive window structure which uses a sapphire plate,
wherein the following expressions (1)-(4) are established between an angle &psgr; as viewed from the optical axis, formed by the C axis of the sapphire and the plane of polarization of light, which is linear polarization, and an angle &thgr; formed by the C axis of the sapphire and the optical axis.
n
=&ohgr;&egr;/{square root over ((&ohgr;
2
cos
2
&thgr;+&egr;
2
sin
2
&thgr;))} (1)
&dgr;=2
&pgr;d
(&ohgr;−
n
)/&lgr; (2)
tan
β
=
(
sin
2
2
ψ
sin
2
δ
+
1
)
-
1
sin
2
ψ
sin
δ
(
3
)
−30≧+20log(tan&bgr;) (4)
where,
&ohgr;: Principal refractive index of the sapphire
&egr;: Secondary refractive index of the sapphire
&lgr;: Wavelength of a transmitted light
d: Thickness of the sapphire
Furthermore, according to the present invention, there is provided an optical module according to the above-mentioned optical module, wherein, when the thickness d of said sapphire plate is 0.28 mm, and N is an integer, any one of the following expressions (5) through (7) is established between said angle &psgr; and said angle &thgr;.
6 degrees≦&thgr;≦10 degrees and (90N−9) degrees≦&psgr;≦(90N+9) degrees (5)
2 degre
Hirose Takaaki
Iwamoto Hiromi
Tatoh Nobuyoshi
Healy Brian
Petkovsek Daniel
Sumitomo Electric Industries Ltd.
LandOfFree
Optical communication module having a constant plane of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Optical communication module having a constant plane of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical communication module having a constant plane of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3048734