Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2001-12-03
2002-11-19
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C372S020000, C372S032000, C372S033000, C372S034000, C372S038020
Reexamination Certificate
active
06483625
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical transmission apparatus used in a wavelength division multiplexed (WDM) optical transmission system. In particular, the invention relates to a WDM optical transmission apparatus in which there is performed a drive control that avoids an occurrence of inter-channel crosstalk caused by wavelength variations during transient states when an apparatus is started and stopped.
BACKGROUND ART
In a WDM optical transmission system, wavelengths of a plurality of optical signals to be wavelength multiplexed are standardized by the ITU (International Telecommunication Union). Most conventional optical transmission apparatuses used in WDM optical transmission systems are provided with a function that performs an automatic wavelength (frequency) control (hereunder abbreviated to AFC) in order to stabilize the wavelength of output light. This AFC function is a function that, for example, detects a wavelength of output light from a laser diode (LD), feeds back the detection result to control the temperature of the LD in order to maintain the wavelength of output light to be constant, which is realized by a so-called wavelength locker or the like.
FIG.
1
and
FIG. 2
are block diagrams showing structural examples of conventional WDM optical transmission apparatus.
In the structural example of
FIG. 1
, light transmitted from an LD
100
is modulated by an external modulator
110
, and its optical signal is output to the exterior via a wavelength locker
120
and an optical filter
150
. In the wavelength locker
120
, a wavelength of the optical signal from the external modulator
110
is detected by a wavelength detecting section
121
and the detection result is transmitted to a wavelength control circuit
122
. In the wavelength control circuit
122
, a signal for controlling the temperature of the LD
100
is generated such that the wavelength of the output light reaches a required target wavelength to be transmitted to a temperature control circuit (ATC)
130
. In the temperature control circuit
130
, the operating temperature of the LD
100
is controlled according to the signal from the wavelength control circuit
122
, and a temperature monitor signal. Furthermore, a drive current to the LD
100
is controlled by a drive current control circuit
140
. As a result, during normal operation, an optical signal is transmitted in a state where its channel interval is constant (for example 0.8 nm). Moreover, by installing an optical filter
150
such as a bandpass filter (BPF) on the output side of the wavelength locker
120
, an occurrence of inter-channel crosstalk caused by wavelength variations at starting and during stopping of the apparatus is suppressed by hardware.
Furthermore, in the structural example of
FIG. 2
, the wavelength locker
120
monitors light emitted from the rear face of the LD
100
and performs a wavelength control. Also by installing an optical switch
160
on the output side of the external modulator
110
, the occurrence of inter-channel crosstalk caused by wavelength variations is suppressed. Here, a modulator may be used as the optical switch
160
.
In a conventional WDM optical transmission apparatus as described above, in order to avoid the occurrence of inter-channel crosstalk, an optical filter, an optical switch or the like is provided. However, since an optical filter, optical switch or the like needs to be provided for each wavelength light, the overall construction of the transmission apparatus becomes complicated, hence causing a problem in that it is difficult to achieve miniaturization and low cost. Furthermore, in a case where an optical filter is used, there is a disadvantage in that a large number of optical filters having different characteristics must be prepared. Moreover, there is also a problem in that by inserting optical filters, optical switches or the like, losses become large.
The present invention takes the above situation into consideration with the object of providing a WDM optical transmission apparatus capable of suppressing an occurrence of inter-channel crosstalk, by controlling the temperature of a light source and its drive current appropriately without optical filters, optical switches or the like.
DISCLOSURE OF THE INVENTION
In order to achieve the above object, a WDM optical transmission apparatus of the present invention used in a WDM optical transmission system for transmitting a wavelength division multiplexed signal light including a plurality of different optical signals, comprises: a light source for generating light whose wavelength is changed according to the temperature and a drive current; temperature control means for controlling the temperature of the light source so that a wavelength at the starting of emission of the light source is stabilized in an allowable range of optical output wavelength set in advance, based on wavelength characteristics for the light source drive current and intervals between adjacent optical signal wavelengths; drive current control means for controlling the drive current applied to the light source according to the allowable range of the optical output wavelength; wavelength control means for detecting a wavelength of light output from the light source and controlling the temperature of the light source based on the detection result, to lead the optical output wavelength into the vicinity of a preset target wavelength; and operation control means for controlling the start and stop of respective control operations of the temperature control means, the drive current control means and the wavelength control means at predetermined timing respectively corresponding to the time of optical output generation and the time of optical output stop.
According to such a construction, during transient states when the apparatus is started and stopped, variations occur in optical output wavelength due to changes of temperature and drive current of the light source. However, the temperature and drive current of the light source are controlled by the temperature control means, the drive current control means and the wavelength control means such that variations of this optical output wavelength are held within the allowable range set in advance. At this time, by controlling the start and suspension of the respective control operations of the temperature control means, the drive current control means and the wavelength control means, by the operation control means at the predetermined timing, it becomes possible to avoid an occurrence of inter-channel crosstalk without installing optical filters, optical switches or the like.
For a specific construction of the abovementioned WDM optical transmission apparatus, the arrangement is preferably such that the operation control means starts the control operation of the temperature control means when the optical output is generated, starts the control operation of the drive current control means when the temperature control is stabilized, starts the control operation of the wavelength control means when the drive current control is stabilized, and furthermore, the operation control means stops the control operation of the wavelength control means when the optical output is stopped, stops the control operation of the drive current control means when the temperature of the light source is stabilized by the control operation of the temperature control means, and stops the control operation of the temperature control means when there is no supply of drive current to the light source and emission is stopped.
Furthermore, the drive current control means may be constituted to perform an automatic current control for controlling the drive current supplied to the light source to be constant, or perform an automatic power control for controlling the drive current such that the optical output power from the light source is kept constant. Moreover, in a case where automatic power control is performed, by providing a circuit construction using a differential amplification method, maximum drive current is restricted
Kiyonaga Tetsuya
Sekiya Motoyoshi
Shimura Yoshitaka
Li Shi K.
Pascal Leslie
Staas & Halsey , LLP
LandOfFree
WDM optical transmission apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with WDM optical transmission apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and WDM optical transmission apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2947426