Coherent light generators – Particular beam control device – Tuning
Reexamination Certificate
1999-01-29
2003-04-01
Ip, Paul (Department: 2828)
Coherent light generators
Particular beam control device
Tuning
C356S416000
Reexamination Certificate
active
06542523
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a wavelength-variable light source apparatus having a wavelength calibration function of emitted light therefrom.
2. Description of the Related Art
Hitherto, normally a semiconductor laser of an external resonator type, which will be hereinafter referred to as LD, has been used as a wavelength-variable light source and an optical filter which is a wavelength selection element has been inserted into an external resonator for providing single-mode oscillation. The wavelength passing through (or reflected on) the optical filter is made mechanically variable, thereby enabling wavelength sweeping in a wide range.
Such a wavelength-variable light source is used to measure the optical characteristics of an optical filter, a communication optical fiber, and the like. Before the measurement conditions are set, it is necessary to calibrate the wavelength of the current light oscillated from the wavelength-variable light source in response to the measurement environment (ambient temperature and the like). For example, a measuring instrument with the wavelength accuracy checked such as a wave meter using a Fabry-Perot interferometer is used to calibrate the wavelength of the wavelength-variable light source.
However, to measure the optical characteristics of an optical filter, a communication optical fiber, and the like, using the conventional wavelength-variable light source, a measuring instrument with the wavelength accuracy checked such as a wave meter needs to be used to calibrate the wavelength of the wavelength-variable light source, thus the wavelength calibration requires a lot of time and labor and an expensive wave meter must be provided, impeding the effective use of the wavelength-variable light source.
Since the wave meter is of large size relative to the main part of the wavelength-variable light source, upsizing and high costs of the wavelength-variable light source result from containing the wave meter in the wavelength-variable light source.
Incidentally,
FIG. 11
shows an example of a wavelength-variable light source apparatus using a wavelength-variable light source. A wavelength-variable light source apparatus
101
shown in
FIG. 11
is made up of a wavelength-variable light source section
102
, a wavelength-variable drive section
103
, a drive control section
104
, a control section
105
, a central processing unit (CPU)
106
, a read-only memory (ROM)
107
, an LD drive section
108
, and a light detection section
109
.
The wavelength-variable light source section (TLS)
102
uses an LD of an external resonator type. The mechanical position of an optical filter forming a part of an external resonator is moved by the wavelength-variable drive section
103
, whereby the external resonance condition is varied and the wavelength of emitted light can be made variable in a wide range.
The wavelength-variable drive section
103
, which is made up of a pulse motor and the like, moves the mechanical position of the optical filter in the wavelength-variable light source section
102
in response to a drive control signal input from the drive control section
104
and outputs a position signal indicating the move position of the optical filter to the drive control section
104
as a rotary encode signal of the pulse motor. The drive control section
104
generates a drive control signal in response to a wavelength-variable control signal input from the control section
105
and outputs the drive control signal to the wavelength-variable drive section
103
and also outputs the position signal (rotary encode signal) input from the wavelength-variable drive section
103
to the control section
105
.
The control section
105
has a function of controlling the relationship between the move position of the optical filter in the wavelength-variable light source section
102
and the wavelength of emitted light. The control section
105
generates a wavelength-variable control signal in response to a wavelength-variable instruction signal input from the CPU
106
and outputs the wavelength-variable control signal to the drive control section
104
for setting the wavelength of emitted light. The control section
105
also checks that the emitted light is set to the set wavelength based on the position signal (rotary encode signal) input from the drive control section
104
, then stops the drive control. Further, the control section
105
converts the position signal (rotary encode signal) input from the drive control section
104
into position data and outputs the position data to the CPU
106
.
The CPU
106
outputs a wavelength-variable instruction signal to the control section
105
for instructing the control section
105
to vary the wavelength of emitted light. The CPU
106
also calculates set wavelength of emitted light based on the position data input from the control section
105
and reads a wavelength correction value to correct the light output level based on the set wavelength from the ROM
107
, then supplies the wavelength correction value to the LD drive section
108
for causing the LD drive section
108
to correct the quantity of a drive current supplied from the LD drive section
108
to the wavelength-variable light source section
102
.
The ROM
107
stores a wavelength calculation processing program which is executed by the CPU
106
and a wavelength correction table setting a number of wavelength correction values for correcting the output level of emitted light in the wavelength-variable light source section
102
corresponding to the position data input from the control section
105
to the CPU
106
.
The LD drive section
108
supplies a drive current to the LD in the wavelength-variable light source section
102
based on a light detection signal input from the light detection section
109
for controlling the output level of emitted light to a constant level. The LD drive section
108
also corrects the drive current so as to correct the light detection characteristic responsive to the wavelength in the light detection section
109
in accordance with the wavelength correction value supplied from the CPU
106
and controls the output level of emitted light to a constant level even if the wavelength of the emitted light from the wavelength-variable light source section
102
is varied.
The light detection section
109
is made up of a lens
109
a
and a light detection element
109
b
. The lens
109
a
emits reference light input from the wavelength-variable light source section
102
via an optical fiber
110
to an optical connection terminal
112
to the light detection element
109
b
as collimated light. The light detection element
109
b
receives incident light through the lens
109
a
and converts the light into a light detection signal having a predetermined voltage level in response to the received light strength with the light reception sensitivity characteristic responsive to the wavelength, then outputs the light detection signal from a detection terminal
113
via a cable
114
to the LD drive section
108
.
Thus, in the conventional wavelength-variable light source apparatus
101
shown in
FIG. 11
, the CPU
106
always monitors the move position in the wavelength-variable drive section
103
and corrects the drive current supplied from the LD drive section
108
to the wavelength-variable light source section
102
in response to the wavelength.
However, in the conventional wavelength-variable light source apparatus
101
shown in
FIG. 11
, the CPU
106
always monitors the move position in the wavelength-variable drive section
103
and corrects the drive current supplied from the LD drive section
108
to the wavelength-variable light source section
102
in response to the wavelength, thus the processing load on the CPU becomes large and installation of the CPU results in an increases in costs of the wavelength-variable light source apparatus.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a wavelength-variable ligh
Ando Electric Co. Ltd.
Finnegan Henderson Farabow Garrett & Dunner LLP
Ip Paul
Nguyen Dung
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