Semiconductor optical amplifier module with monitoring device

Details Semiconductor optical amplifier module with monitoring device Semiconductor optical amplifier module with monitoring device

2002-03-01

2003-12-09

Hellner, Mark (Department: 3663)

Optical: systems and elements

Optical amplifier

C385S092000

Reexamination Certificate

active

06661569

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention The present invention relates to optical communications devices and, more particularly, to an optical semiconductor module for optical amplification application.
2. Description of the Related Art
In general, an optical amplifier for use in optical communications is mainly divided into an optical-fiber amplifier and a semiconductor optical amplifier (SOA). An example of the optical-fiber amplifiers is erbium-doped optical-fiber amplifier (EDFA), in which a light source is pumped into an erbium-doped optical fiber so that the inputted optical signals are amplified through stimulated emission by the erbium element. In contrast, a commonly used semiconductor optical amplifier consists of layered structures formed on a semiconductor substrate in sequence, including an active layer with a multiple (or single) quantum well structure for a fiber amplification, a waveguide layer operable as a broadcast media of the inputted optical signals, a clad layer that encompasses the waveguide layer to confine the inputted optical signals therein, an upper electrode layer, and a lower electrode layer. It is well known that the semiconductor optical amplifier is more advantageous in that the level of the current applied to the upper electrode layer can be adjusted as occasion demands.
However, it is important to maintain a constant ratio between the inputted optical signal power and the outputted optical signal power (or an optical amplification ratio) in the semiconductor optical fiber. That is to say, if the optical amplification ratio of the semiconductor optical amplifier exceeds a threshold value, it can have a bad influence on the operation of other optical elements that are connected to the semiconductor optical amplifier. In addition, if the optical-amplification ratio of the semiconductor optical amplifier is smaller than the threshold value, it can deteriorate the characteristics of the outputted optical signals, such as the signal-to-noise ratio. As a result, a monitoring device is typically employed to ensure that optical characteristics are not affected by a discrepancy in the optical-amplification ratio.
FIG. 1
shows a monitoring device of a semiconductor optical amplifier according to the related art. As shown in
FIG. 1
, the monitoring device includes a semiconductor optical amplifier
110
, a bean splitter
129
, an optical detector
130
, an analog/digital converter (ADC)
140
, a bias circuit
150
, a digital/analog converter (DAC)
160
, and a controller
170
.
The semiconductor optical amplifier
110
amplifies the inputted optical signals within a designated optical-amplification ratio, and outputs the amplified optical signals.
In operation, the beam splitter
120
splits a portion of the optical signals corresponding to x % of the total optical power outputted from the semiconductor optical amplifier
110
(hereinafter referred to as an optical signal sample), then outputs the optical signal sample to the optical detector
130
. The other optical signal outputs corresponding to (100−x) % power are passed through the beam splitter
120
. Meanwhile, the optical detector
130
converts the inputted optical-signal sample from the beam splitter
120
to electric signals and outputs the corresponding electric signals. The analog/digital converter
140
converts the output signals from the optical detector
130
to corresponding digital signals and outputs the converted digital signals to the controller
170
. The controller
170
determines the power of the amplified optical signal that is outputted from the semiconductor optical amplifier
110
based on the digital signal outputs from the converter
140
. In particular, the controller
170
obtains a difference between the amplified optical signal's power and a predetermined power threshold level, then adjusts the current level that is applied to the semiconductor optical amplifier
110
to adjust the optical amplification ratio of the semiconductor optical amplifier
110
. Accordingly, the controller
170
outputs a control signal indicative of the adjusted current level to the digital/analog converter
160
, which then converts the control signal to an analog signal and outputs the converted analog signal to the bias circuit
150
. Finally, the bias circuit
150
applies the current responsive to the control signal to the semiconductor optical amplifier
110
to adjust the gain of the semiconductor optical amplifier
110
. This change in the gain causes the optical amplification ratio of the semiconductor optical amplifier
110
to change. Accordingly, the controller
170
can control the optical-amplification ratio of the semiconductor optical amplifier
110
to maintain at a specific level.
There are some drawbacks in the prior art monitoring device in that it requires extra components, such as a beam splitter
120
for monitoring the outputted optical signal's power. As a result, it increases manufacturing costs. In addition, the semiconductor optical amplifier
110
, the beam splitter
120
, and the optical detector
130
must be positioned precisely in an array, and further require other devices (not shown) for the same application. Furthermore, the maximum output power of the semiconductor optical amplifier
110
suffers as a portion of the outputted optical signals are extracted during the monitoring operation.
In summary, the conventional structure of the semiconductor optical amplifier module that is mounted with the semiconductor optical amplifier and the monitoring device in a housing has drawbacks associated with high manufacturing cost, low integration due to the deployment of the beam splitter and additional optical components, and a loss in the maximum output power.
SUMMARY OF THE INVENTION
The present invention overcomes the above-described problems, and provides additional advantages by providing a semiconductor optical amplifier module with a monitoring device that has a low manufacturing cost, a high integration capability, and a maximum output power.
According to an aspect of the invention, there is provided a semiconductor optical amplifier with a monitoring device, which includes: a housing having a window on both sides of opposite walls for forming a path of a first optical fiber and a second optical fiber, respectively; a semiconductor optical amplifier fixated in the housing for amplifying the inputted optical signals and outputting the amplified optical signals; a first supporter for supporting the first optical fiber; and, a second supporter for supporting the second optical fiber.
According to another aspect of the invention, the semiconductor optical amplifier further includes a first optical detector that is arrayed in such a way to detect the non-coupled light generated in the line of the first optical fiber.
The foregoing and other features and advantages of the invention will be apparent from the following, more detailed description of preferred embodiments as illustrated in the accompanying drawings in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, the emphasis instead is placed upon illustrating the principles of the invention.


REFERENCES:
patent: 4995696 (1991-02-01), Nishimura et al.
patent: 6366396 (2002-04-01), Hayashi
patent: 6384961 (2002-05-01), Lawrence

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