GB2340617A - Controllable variable wavelength filter - Google Patents
Controllable variable wavelength filter Download PDFInfo
- Publication number
- GB2340617A GB2340617A GB9918645A GB9918645A GB2340617A GB 2340617 A GB2340617 A GB 2340617A GB 9918645 A GB9918645 A GB 9918645A GB 9918645 A GB9918645 A GB 9918645A GB 2340617 A GB2340617 A GB 2340617A
- Authority
- GB
- United Kingdom
- Prior art keywords
- wavelength
- variable
- wavelength filter
- gain amplifier
- transmission
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/29—Repeaters
- H04B10/291—Repeaters in which processing or amplification is carried out without conversion of the main signal from optical form
- H04B10/293—Signal power control
- H04B10/294—Signal power control in a multiwavelength system, e.g. gain equalisation
- H04B10/2941—Signal power control in a multiwavelength system, e.g. gain equalisation using an equalising unit, e.g. a filter
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/0121—Operation of devices; Circuit arrangements, not otherwise provided for in this subclass
- G02F1/0123—Circuits for the control or stabilisation of the bias voltage, e.g. automatic bias control [ABC] feedback loops
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
- H01S3/10—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
- H01S3/10007—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers
- H01S3/10023—Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating in optical amplifiers by functional association of additional optical elements, e.g. filters, gratings, reflectors
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Optics & Photonics (AREA)
- Nonlinear Science (AREA)
- Plasma & Fusion (AREA)
- General Physics & Mathematics (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Optical Communication System (AREA)
Abstract
Light transmitted by a variable wavelength filter 101 is branched by a light branching unit 102, photoelectrically converted by a photodetector 103, amplified by a variable gain amplifier 104, and transmitted to a controller 107. An output of the variable gain amplifier is also synchronously detected by a synchronous detector 105 with a modulation frequency of micro transmission wavelength modulation by an oscillator 108, and then transmitted to the controller. The transmission wavelength of the variable wavelength filter is controlled by the controller. The variable gain amplifier has a predetermined gain corresponding to each wavelength (channel), which can be set in stepwise manner by the controller.
Description
2340617 Variable Wavelength Filter Device and Control Method of Variable
Wavelength Filter BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to a variable wavelength filter device and a method of controlling a variable wavelength filter, which are suitable for selection/extraction of a signal light in a wavelength -multiplexing communication according to a wavelength division multiplexing (WDM) system.
(ii) Description of the Related Art
In an optical communication system using a wavelength division multiplexing system, during relay, reception and the like, it is necessary to selectively extract a light signal of a desired wavelength from a plurality of light signals of multiplexed wavelengths. In order to select/extract the light signal havin g the desired wavelength from a plurality of light signals multiplexed with different wavelengths, a variable wavelength filter capable of controlling a transmission wavelength in accordance with the desired light signal is used to selectively transmit a desired specified wavelength.
Disclosed in Japanese Patent Application Laid-Open No. 326770/1997 is a gain control method for use in a linear relay in an optical communication system by a wavelength division multiplexing system. Also disclosed in Ja panese Patent Application Laid-Open No. 237242/1994 (USP No.
2 5,469,288) is an example of a variable wavelength narrow bandwidth optical filter and a control method thereof for use in the optical communication system by the wavelength division multiplexing system.
In the system disclosed in the Japanese Patent Application Laid-Open No. 326770/1997, an optical direct amplifier is used for amplifying a plurality of input optical signals. Further, an automatic gain controller is applied for controlling the amplification factor of the optical direct amplifier with respective predetermined amplification factors corresponding to the plurality of input optical signals, by controlling bias currents of the optical direct amplifier.
This is a type of an automatic gain controlling system using the optical direct amplifier for amplifying the light signals themselves. But this type does not have a function to perform a control over the amplification factor of a light detection signal of a light quantity detection circuit, which detects light signals in outputs of the variable wavelength optical filter.
On the other hand, in the system disclosed in the Japanese Patent Application Laid-open No. 237242/1994, a light detection signal detected from the output of a variable wavelength narrow bandwidth optical filter is amplified with a fixed gain, a low-frequency signal is applied to the amplified detection signal for synchronous detection to fetch an error signal, and the low-frequency signal is superimposed into the error signal and fed back to a drive circuit of the variable wavelength narrow bandwidth optical filter. By the 3 feedback, control is performed in such a manner that a transmission wavelength of the variable wavelength narrow bandwidth optical filter coincides with a transmitted light signal wavelength.
As disclosed in the Japanese Patent Application Laid-Open No. 237242/1994, the conventional amplifier connected to a photodetector, which detects the output of the variable wavelength filter, has the fixed gain. This is because if an ordinary automatic gain control (AGC) amplifier is used as the amplifier connected to the photodetector detecting the output of the variable wavelength filter, the following problem could be caused. By characteristic change of the AGC amplifier, a micro modulated signal component of the superimposed low frequency signal, which is applied to obtain the error signal, is cut off, or interfered through the AGC amplification. Therefore, the dynamic range of a control system becomes narrow. Further, if there is a light intensity difference between input multiplexed wavelengths (channels), an appropriate transmission wavelength control of the variable wavelength filter cannot be performed in some channels. Additionally, the ordinary automatic gain control amplifier is expensive, and further provides an inferior characteristic in a frequency bandwidth of several kHz for use in ordinary synchronous detection.
On the other hand, when the ordinary fixed gain amplifier is used as the amplifier, at a low input level, a sufficient signal noise ratio (SIN) cannot be obtained, and at a high input level, outputs are disadvantageously 4 saturated and signals are cut off.
SUMMARY OF THE INVENTION
The present invention has been developed in consideration of the above-mentioned circumstances, and an object thereof is to provide a variable wavelength filter device and a control method of a variable wavelength filter which is capable of preventing from cutting off, or interfering with a micro modulated signal superimposed to 10 obtain an error signal.
It is another object of the invention to provide a variable wavelength filter device and a control method thereof, in which an output level of the variable wavelength filter can be amplified in an optimum range and a dynamic is range of a control system can be enlarged.
It is further an object of the invention to provide a variable wavelength filter device and a control method thereof, which is capable of shortening a time required for stabilizing the control system after the switching of a reception wavelength.
To attain the above-mentioned and other objects, according to the present invention there is provided a variable wavelength filter device, comprising:
a variable wavelength filter capable of transmitting a specified wavelength component of a light signal and changing a transmission wavelength; a drive circuit for controlling the variable wavelength filter to change the transmission wavelength; r a photodetector for detecting an intensity of a transmission light of the variable wavelength filter; a variable gain amplifier capable of amplifying an output of the photodetector and changing an amplification factor; and a control system for controlling the drive circuit based on an output of the variable gain amplifier to allow a peak of the transmission wavelength of the variable wavelength filter to coincide with a wavelength of a -predetermined incident light, and changing the amplification factor of the variable gain amplifier in accordance with the transmission wavelength.
The variable gain amplifier may be a variable gain amplifier capable of setting the amplification factor for each transmission wavelength of the variable wavelength filter in a stepwise manner.
The control system may include:
means for storing an optimum amplification factor to be set in the variable gain amplifier for each required transmission wavelength of the variable wavelength filter; and means for setting the variable gain amplifier to the stored optimum amplification factor of each transmission wavelength every time the required transmission wavelength of the variable wavelength filter is switched.
The control system may further include means for detecting the output of the variable gain amplifier to scan each wavelength of the transmission wavelength when the 6 system is started, and obtaining the optimum amplification factor for each transmission wavelength of the variable gain amplifier.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a block diagram showing a receiving apparatus including a variable wavelength filter device according to an embodiment of the present invention; Figs. 2A and 2B are waveform diagrams showing a waveform relative to an optical filter transmission light intensity and a synchronous detector output wavelength to describe operation in the receiving apparatus of Fig. 1; Fig. 3 is a flowchart showing an operation for determining amplification factors (gains) of a variable gain amplifier for each wavelength (channel) according to the invention; and Fig. 4 is a flowchart showing an operation for switching a wavelength in the variable wavelength filter according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of a variable wavelength filter device according to the present invention will be described hereinafter with reference to Figs. 1 to 4.
Referring to Fig. 1 showing a receiving apparatus to which the variable wavelength filter device according to the embodiment of the present invention, the variable wavelength filter device comprises a variable wavelength filter 101, a 7 light branching unit 102, a photodetector 103, a variable gain amplifier 104, a synchronous detector 105, a first A/D (analog-to-digital) converter 106, a controller 107 including a CPU and a memory, an low frequency oscillator 108, a second A/D (analog-to-digital) converter 109, a D/A (digital-toanalog) converter 110, a drive circuit 111 and a signal adder 113. Further, by adding a receiver 112, the receiving apparatus is constructed.
The variable wavelength filter 101 receives input -light signals including a plurality of multiplexed wavelengths corresponding to transmission channels, and transmits a light signal having a predetermined wavelength bandwidth component corresponding to a desired transmission channel. With regard to the variable wavelength filter 101, the predetermined wavelength bandwidth is changed by a control from the drive circuit 111. The light branching unit 102 branches a transmitted light outputted from the variable wavelength filter 101, and supplies one light to the receiver 112 and the other light to the photodetector 103. The photodetector 103 converts the branched light into an detected electrical signal, which is supplied to the variable gain amplifier 104. The variable gain amplifier 104 is an amplifier having an amplification factor controlled in a stepwise manner by the controller 107. The amplified output from the variable gain amplifier 104 is supplied both to the synchronous detector 105 and the first A/D converter 106.
The synchronous detector 105, which is constituted of a so-called lockin amplifier or the like, synchronously detects the amplified output of the variable gain amplifier 104 with reference to an oscillation output of the oscillator 108. Thus, the synchronous detector 105 delivers a primary (first order) differential waveform corresponding to a difference between the filtered transmission wavelength and the signal light wavelength in the vicinity of a transmission peak wavelength. Such synchronous detection is well known and disclosed in USP No. 5,469,288, for example. The synchronous detector 105 supplies its output as an error signal to the second A/D converter 109. The second A/D converter 109 converts the analog detection output of the synchronous detector 105 into a digital value. On the other hand, the first A/D converter 106 converts the analog output of the variable gain amplifier 104 into a digital value and supplies the value to the controller 107.
The controller 107, which includes at least a CPU and a memory, controls the variable wavelength filter 101 based on wavelength bandwidth selection corres ponding to channel selection data and the error signal detected by the synchronous detector 105 through the D/A converter 110, the signal adder 113 and the drive circuit 111. The D/A converter converts a digital control signal outputted from the controller 107 for controlling the transmission wavelength of the variable wavelength filter into an analog signal and supplies the signal through the signal adder 113 to the drive circuit 111. Therefore, the controller 107 performs a control to allow the transmission wavelength peak of the variable wavelength filter 101 to coincide with an incident light 9 wavelength based on the error signal, together with channel selection. Further, the controller 107 designates the corresponding gains in the variable gain amplifier 104 according to each multiplexed wavelength (channel).
The oscillator 108 outputs a micro oscillation output of a low frequency fO and supplies it to the synchronous detector 105 as a reference signal, and to a signal adder 113 to produce a drive control signal to be supplied to the drive circuit 111. The signal adder 113 adds -the outputs of the D/A converter 110 and the oscillator 108.
The drive circuit 111 drives the variable wavelength filter 101 based on the control signal from the adder 113. By driving the variable wavelength filter 101 based on the control signal from the adder 113, the variable wavelength filter 101 selectively transmits a light signal of a required wavelength bandwidth corresponding to the selected channel while vibrating transmitting wavelength with a micro range.
The receiver 112 receives the light signal of the required wavelength bandwidth selectively transmitted from the variable wavelength filter 101.
The operation of the variable wavelength filter device shown in Fig. 1 will next be described with reference to Figs. 1 and 2. In Fig. 1, the wavelength multiplexed signal lights are transmitted to the variable wavelength filter 101, and the filtered wavelength bandwidth component in the multiplexed signal lights is selected. The selected light signal is branched by the light branching unit 102, and - 10 received by the receiver 112. On the other hand, the other branched one is photoelectrically converted by the photodetector 103 to detect light intensity. The output of the photodetector 103 is amplified by the variable gain amplifier 104, and then supplied to the synchronous detector 105.
The transmi/,odtting wavelength in the variable wavelength filter 101 is controlled by the drive circuit 111 and, in this case, in order to generate the error signal, the transmitting wavelength is minutely modulated with the oscillation frequency fO of the oscillator 108. As shown in Fig. 2, when the transmission light intensity (Fig. 2A) of the variable wavelength filter 101 is synchronously detected by the synchronous detector 105 with the oscillation frequency fO of the oscillator 108, the output (Fig. 2B) forms a primary differential waveform of a transmission wavelength characteristic (Fig. 2A) of the variable wavelength filter 101. Specifically, as shown in Figs. 2W and 2(B) in the vicinity of the transmission peak wavelength, the synchronous detection output is primarily/approximately proportional to the difference of the filter transmission wavelength and the signal light wavelength, and can be regarded as the error signal to perform the transmission wavelength control of the variable wavelength filter 101.
The output of the synchronous detector 105 is converted by the second A/D converter 109 and supplied to the controller 107 as the error signal. The variable wavelength filter 101 is controlled through the drive circuit 111 and the D/A converter 110 by the controller 107 so as to minimize the error signal.
In this case, assuming that an ordinary automatic gain control (AGC) amplifier is applied to the variable gain amplifier 104, by a characteristic of the AGC amplifier, the micro modulated component of the oscillation frequency fO superimposed is cut off or interfered. On the other hand, assuming that an ordinary fixed gain amplifier is applied instead of the variable gain amplifier 104, when the input light intensity is low, a sufficient signal-to-noise ratio (SIN) cannot be obtained, otherwise when the input light intensity is high, the output of the amplifier 104 is disadvantageously saturated and thus the micro modulated component, which is used to produce the error signal, becomes cut off.
To the contrary, according to the present invention, a variable gain amplifier having the stepwised amplification factors (gains) is used as the variable gain amplifier 104. The controller 107 selects one of the stepwised amplification factors for each channel. To determine each amplification factor for the each channel, the output level of the variable gain amplifier is AID converted by the first AID converter 106, and taken into the controller 107. Then, the controller 107 controls the variable gain amplifier 104 in such a manner that the output level of the variable gain amplifier 104 is placed in a range in which the error signal can be optimally detected by the synchronous detector 105.
In the ordinary wavelength multiplexing - 12 communication, the signal light intensity of each multiplexed wavelength (channel) differs. Therefore, to determine the amplification factor of the variable gain amplifier 104 according to each wavelength, for example, when the receiving apparatus is started up, the output of the variable gain amplifier 104 is detected while scanning the variable wavelength filter 101, i.e., changing the transmission wavelength for all channels. By detecting the maximum value of the output of the variable gain amplifier 104 -corresponding to each channel, while scanning, each amplification factor (gain) in which the error signal can be optimally detected by the synchronous detector 105 is calculated and stored in the controller 107. Subsequently, every time the reception wavelength is switched, the amplification factor stored beforehand is set to the variable gain amplifier 104. In this case, it is unnecessary to determine the amplification factor of the variable gain amplifier 104 again and again every time the reception wavelength is switched. Therefore, the time required for stabilizing the control system can be shortened.
Flowcharts showing an operation for determining amplification factors (gains) of the variable gain amplifier for each wavelength (channel) and an operation for switching a wavelength in the variable wavelength filter are shown in Figs. 3 and 4.
According to the embodiment of the invention, the dynamic range of the control system is enlarged. This is because, by applying the variable gain amplifier 104 capable - 13 Of setting the amplification factor in the stepwise manner by the controller 107, without cutting off or interfering with the micro modulated signal of the oscillation frequency fO superimposed to obtain the error signal by the amplifier, the output level of the variable gain amplifier 104 can be set in an optimum range.
Moreover, the time required for stabilizing the control system after the switching of the reception wavelength can be shortened. This is because the optimum -amplification factor of each wavelength is stored beforehand, and the stored optimum amplification factor is set to the variable gain amplifier every time the reception wavelength is switched.
One embodiment of the present invention has been described above in detail, but the present invention is not limited to the embodiment. For example, in the above mentioned embodiment, the synchronous detector 105 is used to detect the error signal for controlling the variable wavelength filter, but without using the synchronous detector 105 the output of the variable gain amplifier 104 may be A/D converted and taken into the controller 107, so that the output of the variable wavelength filter is maximized/controlled step by step.
Claims (8)
1. A variable wavelength filter device, comprising: a variable wavelength filter capable of transmitting a specified wavelength component of a light signal and changing a transmission wavelength; a drive circuit for controlling said variable wavelength filter to change said transmission wavelength; a photodetector for detecting an intensity of a transmission light of said variable wavelength filter; a variable gain amplifier capable of amplifying an output of said photodetector and changing an amplification factor; and a control unit for controlling said drive circuit is based on an output of said variable gain amplifier to allow a peak of the transmission wavelength of said variable wavelength filter to coincide with a wavelength of a predetermined incident light, and changing the_ amplification factor of said variable gain amplifier in accordance with the transmission wavelength.
2. The variable wavelength filter device according to claim 1 wherein said variable gain amplifier is a variable gain amplifier capable of setting the amplification factor for each transmission wavelength of said variable wavelength filter in a stepwise manner.
3. The variable wavelength filter device according - 15 to claim 1 or 2 wherein said control unit comprises: means for storing an optimum amplification factor to be set to said variable gain amplifier for each required transmission wavelength of said variable wavelength filter; and means for setting said variable gain amplifier to said stored optimum amplification factor of each transmission wavelength every time the required transmission wavelength of said variable wavelength filter is switched.
4. The variable wavelength filter device according to claim 3 wherein said control unit further comprises means for detecting the output of said variable gain amplifier while each wavelength of said transmission wavelength is scanned, and obtaining the optimum amplification factor for said each transmission wavelength of the variable gain amplifier.
5. A method of controlling a variable wavelength filter including a variable wavelength filter capable of transmitting a specified wavelength component of a light signal and changing a transmission wavelength, a drive circuit for driving/controlling said variable wavelength filter to change said transmission wavelength, a photodetector for detecting an intensity of a transmission light of said variable wavelength filter, and an amplifier for amplifying an output of said photodetector, comprising:
- 16 controlling a gain of said amplifier in accordance with a required transmission wavelength; and controlling said variable wavelength filter to allow a peak of the transmission wavelength of said variable wavelength filter to coincide with a wavelength of a predetermined incident light.
6. The control method of the variable wavelength filter according to claim 5, wherein further comprising detecting an output of said variable gain amplifier beforehand while each wavelength of the required transmission wavelength of said variable wavelength filter is scanned; obtaining an optimum amplification factor of said each transmission wavelength of the variable gain amplifier; storing the optimum amplification factor of the each transmission wavelength; and setting said stored optimum amplification factor of each transmission wavelength into said variable gain amplifier when a transmission wavelength of said variable wavelength filter is switched.
7. A variable wavelength filter device substantially as herein described with reference to the drawings.
8. A method of controlling a variable wavelength filter substantially as herein described with reference to the drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10223973A JP2943802B1 (en) | 1998-08-07 | 1998-08-07 | Variable wavelength filter device and variable wavelength filter control method |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB9918645D0 GB9918645D0 (en) | 1999-10-13 |
| GB2340617A true GB2340617A (en) | 2000-02-23 |
| GB2340617B GB2340617B (en) | 2001-03-07 |
Family
ID=16806589
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9918645A Expired - Fee Related GB2340617B (en) | 1998-08-07 | 1999-08-06 | Variable wavelength filter device and control method of variable wavelength filter |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JP2943802B1 (en) |
| GB (1) | GB2340617B (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4789847B2 (en) * | 2007-04-18 | 2011-10-12 | 日本電信電話株式会社 | Optical receiver and method for stabilizing operating point of optical interferometer used therefor |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0857994A2 (en) * | 1997-01-10 | 1998-08-12 | Gpt Limited | Method and apparatus for operating an optical modulator |
| US5933262A (en) * | 1996-04-23 | 1999-08-03 | Nec Corporation | Optical amplification device and wavelength multiplexed light transfer apparatus using the same |
-
1998
- 1998-08-07 JP JP10223973A patent/JP2943802B1/en not_active Expired - Fee Related
-
1999
- 1999-08-06 GB GB9918645A patent/GB2340617B/en not_active Expired - Fee Related
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5933262A (en) * | 1996-04-23 | 1999-08-03 | Nec Corporation | Optical amplification device and wavelength multiplexed light transfer apparatus using the same |
| EP0857994A2 (en) * | 1997-01-10 | 1998-08-12 | Gpt Limited | Method and apparatus for operating an optical modulator |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9918645D0 (en) | 1999-10-13 |
| GB2340617B (en) | 2001-03-07 |
| JP2000059310A (en) | 2000-02-25 |
| JP2943802B1 (en) | 1999-08-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20130806 |