Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2001-01-17
2003-07-01
Bovernick, Rodney (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S088000, C385S092000, C385S094000
Reexamination Certificate
active
06585426
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical module to be used in fields of optical communications and optical information processing, for example, and more particularly, to an optical module for converting optical/electric signals into electric/optical signals by optically connecting an optical element having electric wirings with an optical fiber held by a ferrule and having a tip end portion without jacketing layers that is projecting from the ferrule.
2. Description of the Background Art
In recent years, in conjunction with a drastic increase in the amount of data communications, there is an increasing demand for a photo-detecting or light-emitting optical module for handling high speed optical signals with the optical signal speed of over Gbit/sec (Gbps), for example, and its realization at a cheaper cost. In view of this demand, there are many reports of a method for realizing an optical axis alignment of an optical element and an optical fiber by a mechanical positioning alone (the passive alignment method) by providing a V-groove on a silicon substrate. There are also reports of a technique for molding this optical element mounted silicon substrate together with lead frames.
In the conventional passive alignment method, in the case of processing high speed signals with the optical signal speed over 10 Gbps, it is known that the use of materials having a lower dielectric constant than silicon is advantageous because of the decrease of the parasitic capacity. However, this in turn requires signal line wirings with very minute intervals so that there is a problem that it becomes difficult to manufacture a mold package using lead frames which is advantageous for realization of low cost.
FIG. 1
shows a perspective view of a structure of a conventional optical module. This optical module is a photo-detecting optical module using an ordinary resin package with metallic lead frames, which is manufactured by mounting a photo-diode having an equivalent frequency characteristic as that of a photo-detecting optical module of the present invention shown in
FIG. 7
to be described below and a pre-amplifier IC on a package made of a uniform resin material and having a shape in which metallic leads are independently projected into the lateral directions. Namely, in this conventional optical module, a frame
92
is attached on a plastic substrate
91
to enclose its surrounding, and a quartz glass V-groove substrate
93
is provided at an approximate center of the plastic substrate
91
inside this frame
92
. A photo-diode
11
is implemented on this quartz glass V-groove substrate
93
, and this photo-diode
11
and an optical fiber
5
are optically connected as a tip end portion
5
a
without jacketing layers of the optical fiber
5
abuts against this photo-diode
11
.
The optical fiber
5
is fixed by being set in a V-groove
93
a
that is formed on the quartz glass V-groove substrate
93
along the optical fiber
5
underneath the optical fiber
5
, and a portion projecting out from the quartz glass V-groove substrate
93
is held by a ferrule
7
, where this ferrule
7
is fixedly held at a notch section
92
a
formed on the frame
92
.
Also, a pre-amplifier IC
9
is provided adjacent to one end of the quartz glass V-groove substrate
93
on the plastic substrate
91
, and this pre-amplifier IC
9
is electrically connected to the photo-diode
11
by bonding wires.
In addition, metallic lead frames
94
for pre-amplifier IC and metallic lead frames
95
for signals are provided on the plastic substrate
91
, and one ends of these metallic lead frames
94
and
95
are electrically connected to the pre-amplifier IC
9
by bonding wires while the other ends are projected outside the plastic substrate
91
.
In order to evaluate a receiving bandwidth of the conventional optical module in the above configuration, as shown in
FIG. 2
, this optical module was mounted on a glass epoxy frequency characteristic evaluation substrate
51
on which a plurality of electrode pads
52
, signal lines
53
in a coplanar guide structure, and an SMA type high frequency connector
54
are formed, and they were electrically connected. Then, the receiving characteristic of the conventional optical module shown in
FIG. 1
was evaluated in this connection configuration, to obtain the receiving bandwidth measurement result as shown in FIG.
3
.
As can be seen in the receiving bandwidth evaluation result shown in
FIG. 3
, for this conventional optical module, large ripples which are probably caused by electrical reflections were appearing, and a large degradation of the frequency characteristic was observed. In this type of optical module, a characteristic impedance changes at a portion where the signal transmission leads are projected from inside the package to outside, so that the electrical reflections or resonances can occur easily and these electrical reflections or resonances can cause the degradation of the high frequency characteristic. In practice, an effort to prevent the degradation of the high frequency characteristic is made by cutting the signal line leads short and carefully implementing the optical module such that no gap is formed between a package of the optical module and the glass epoxy frequency characteristic evaluation substrate
51
.
However, the wiring pattern of the glass epoxy frequency characteristic evaluation substrate
51
is usually formed at approximately 1 mm inner side of the edge as indicated by “d” in
FIG. 2
, so that this gap of 1 mm remains as a cause of the electrical reflections. For this reason, the large ripples that are probably caused by the electrical reflections were appearing and the large degradation of the frequency characteristic was observed as shown in FIG.
3
.
FIG. 4
shows the conventional optical module of
FIG. 1
implemented on an optical signal received waveform evaluation substrate which is manufactured by mounting a main amplifier IC
82
on a glass epoxy substrate
81
similar to the glass epoxy frequency characteristic evaluation substrate
51
of
FIG. 2
, in order to carry out the 10 Gbps optical signal received waveform evaluation with respect to a photo-detecting optical module using a resin package with metallic lead frames in a form of the conventional optical module of FIG.
1
. Note that the main amplifier IC
82
is an amplifier having an automatic gain control (AGC) function of the operation frequency bandwidth approximately equal to 10 GHz, which outputs signals having a constant amplitude by uniformly amplifying the received signals as amplified by the pre-amplifier IC
9
used in the conventional optical module of FIG.
1
. Using such an optical signal received waveform evaluation substrate, it is possible to output electric signals suitable for the bit error rate characteristic evaluation that is often used for the received waveform observation and the transmission characteristic evaluation.
FIG. 5
shows the evaluation result for the conventional optical module of
FIG. 1
obtained by using the optical signal received waveform evaluation substrate of FIG.
4
. In this evaluation, the received waveform outputted from the main amplifier IC
82
at a time of receiving optical signals modulated by 10 Gbps pseudo-random pattern (NRZ2
23
−1) with an average power of −10 dBm was observed using a wide bandwidth oscilloscope having a bandwidth of 20 GHz.
FIG. 5
shows the observed waveform, which is a largely degraded waveform compared with the correct eye pattern. Also, when the bit error rate characteristic was evaluated in a vicinity of the average power of −10 dBm using the optical signal received waveform evaluation substrate of
FIG. 4
, it was impossible to realize a completely error free operation without any code recognition error.
Thus the conventional optical module package is associated with a problem that the implementation to connect signal line leads to an external substrate requires considerable cares in order to transmit the high speed sign
Amano Michiyuki
Ishihara Noboru
Kurosaki Takeshi
Nakamura Makoto
Okayasu Masanobu
Bovernick Rodney
Kilpatrick & Stockton LLP
Nippon Telegraph and Telephone Corporation
Pak Sung
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