JPH09312631A - Optical transmitter and control method thereof - Google Patents

Abstract

It is an object of the present invention to maximize the use of the variable wavelength range of a variable wavelength LD and to reduce the difference in the optical output intensity of an optical transmitter emitting light in a communication system. . A wavelength tunable light source, and wavelength detection means for detecting the wavelength of the wavelength tunable light source and the wavelength on the transmission line by sweeping the wavelength of the wavelength tunable filter, based on the wavelength detection result by the wavelength detection means, A wavelength-multiplexed optical communication system for setting the wavelength of the wavelength tunable light source to a constant wavelength interval from one wavelength on the transmission line, and thereafter controlling the wavelength of the wavelength tunable light source so as to maintain the constant wavelength interval. The optical transmitter includes a light intensity adjusting means and a light intensity monitoring means for increasing or decreasing the light output of the variable wavelength light source, and makes the light intensity of the light output of the optical transmitter on the transmission line equal to the light intensity of the adjacent wavelength. It is characterized by controlling so that

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing communication system, and more particularly to an optical transmitter used for wavelength division multiplexing communication.

[0002]

2. Description of the Related Art A wavelength division multiplex communication system can have a large number of independent channels in one transmission line. Since multiplexing on the time axis such as frame synchronization is not required, it is not necessary to match the transmission speed of each channel, which is suitable for multimedia communication that requires network flexibility.

As an example of the wavelength division multiplex communication system, there is a system in which each terminal station has a pair of variable wavelength optical transmitters and optical receivers. The terminal station that transmits the wavelength of the variable wavelength light source of the optical transmitter is a wavelength that is not currently used for communication (wavelength multiplex communication
Corresponding to the "channel". On the other hand, the receiving end station has the center wavelength of the transmission spectrum of the wavelength tunable filter of the optical receiver (the optical bandpass filter that can tune the center wavelength of the transmission spectrum) at the reception wavelength (hereinafter The wavelength range that can be used in the wavelength division multiplexing communication system is determined by the wavelength tunable range of the optical transmitter and the optical receiver. The interval) is determined by the width of the transmission spectrum of the wavelength tunable filter of the optical receiver.

As the wavelength tunable light source, a wavelength tunable semiconductor laser (hereinafter, the semiconductor laser is called LD) can be used. At the present time, the practical level is a multi-electrode DBR (Distributed Bragg Reflector) type or DFB (Distributed Feed Back) type, and the wavelength variable width is several nm. As an example, OQE (Optical and
Quantum Electronics) 89-116, "Three-electrode long resonator λ / 4 shift MQW-DFB laser".

As the wavelength tunable filter, a Fabry-Perot resonator type filter can be used. Wavelength variable width is several nm to several tens of nm, half-value width of transmission spectrum (wavelength width at half level of peak) is 0.01 nm to
Practical level is about 0.1 nm. As an example, a conference draft ECOC (Europian Conference on
Optical Communication) '90 -605, "A field-worthy, h
igh-performance, tunablefiber Fabry-Perot filter "
The ones mentioned can be mentioned.

In a wavelength division multiplexing communication system using such a wavelength tunable light source and a wavelength tunable filter, a wavelength control system of an optical transmitter is required, in which the transmission wavelengths of each terminal station do not interfere with each other and the number of channels can be increased as much as possible. . For example, the system described in Japanese Patent Application No. 6-296660 is one of them. The outline will be described below.

FIG. 5 is a block diagram of an optical communication system. It is a star network. Although many terminal stations are connected to the network, only four terminal stations are shown in order to avoid complication of the drawing. Terminal stations 511 to 514, optical node 511
-514, star coupler 530, optical fibers 541-5
44, 551 to 554. Optical node 521-
524 includes an optical transmitter 560, an optical receiver 570, and an optical branching device 580. The terminal stations 511 to 514 are connected to the network by optical nodes 511 to 514, respectively. Each of the optical nodes 511 to 514 has an optical fiber 541 for transmission.
544 and the receiving optical fibers 551 to 554 are connected to the star coupler 530. The transmission light from the optical transmitter 560 is transmitted through the optical fibers 541 to 544 for transmission to the star coupler 5.
Sent to 30. The star coupler 530 evenly distributes the transmitted light to the respective receiving optical fibers 551 to 554 and sends it to the respective optical nodes 511 to 514. Optical fiber 5 for reception
Incident light from 51 to 554 is divided into two by an optical branching device 580 and input to an optical receiver 570 and an optical transmitter 560. With this configuration, the transmission light of the own station enters the wavelength tunable filter in the optical transmitter 560 together with the transmission light of the other station.
Further, the optical receiver 570 selects and receives the transmission data addressed to itself.

FIG. 6 is a block diagram of the optical transmitter 560. As shown in the figure, the present optical transmitter includes a wavelength control system 101, a wavelength tunable LD 102, a wavelength tunable wavelength tunable filter 103, a wavelength tunable LD drive circuit 104, a wavelength tunable filter drive circuit 105, a light receiving element 106, an amplifier 107, and a discriminator. 10
8, optical modulator 109, optical switch 110, optical combiner 11
1.

The wavelength control system 101 controls the LD drive circuit 104 and the wavelength tunable filter drive circuit 105 based on the output signal of the discriminator 108, and controls the emission wavelength of the wavelength tunable LD 102 and the wavelength tunable filter 103. I do. This wavelength control operation is controlled by the terminal station. Wavelength control system 10
1 is an arithmetic processing circuit, a storage element, an A / D converter, a D / A
Consists of a converter, etc. The memory element stores parameters and operation procedures necessary for the wavelength control operation.

Variable wavelength LD 102, variable wavelength filter 1
03 uses the above-mentioned element. Bandwidth of transmission spectrum of tunable filter 103 (half-value width. Hereinafter, "λFB")
Is the main factor that determines the wavelength spacing Δλ between channels. λFB is set to an appropriate value that is a fraction of Δλ or less (for example, about 1/10). Further, the wavelength variable range of the wavelength variable filter 103 is larger than the wavelength variable range of all the wavelength variable LDs in the system.

The optical modulator 109 intensity-modulates the optical output of the wavelength tunable LD 102 with a transmission signal. When directly modulated by the current injected into the wavelength tunable LD 102, a wavelength variation of about 0.1 nm occurs, so in this example, the external intensity modulation method by the optical modulator 109 is used.

The tunable LD drive circuit 104 includes a tunable LD control voltage (hereinafter referred to as "V") from the wavelength control system 101.
Tunable LD to have a wavelength corresponding to "L")
102 is driven (current is injected). When the above-mentioned three-electrode long resonator λ / 4-shift MQW-DFB laser is used, the output of the wavelength tunable LD control voltage VL is three for the three electrodes. The amount of change in VL is proportional to the amount of change in wavelength of the wavelength tunable LD 102. The amount of change in VL corresponding to Δλ is Δ
VL. The wavelength tunable LD control voltage VL corresponding to the shortest wavelength in the wavelength tunable range of the wavelength tunable LD 102 is set to VLMI.
The variable wavelength LD control voltage VL corresponding to N and the longest wavelength is VLMAX. VL step VLS during wavelength control
Is set based on Δλ, λFB, etc. VL change amount ΔV
A value of about 1/20 from the number of L is suitable.

The tunable filter drive circuit 105 includes a tunable filter control voltage (hereinafter,
The wavelength tunable filter 103 is driven so as to have a wavelength corresponding to “VF”). The amount of change in VF is proportional to the amount of change in wavelength of the wavelength tunable filter 103. The amount of change in VF corresponding to Δλ is ΔVF. The step VFS of VF at the time of wavelength control is set to a value corresponding to VLS. Corresponding here, the change amount of the wavelength of the variable wavelength LD 102 when the variable wavelength LD control voltage VL is changed by the step VLS and the wavelength of the variable wavelength filter 103 when the variable wavelength filter control voltage VF is changed by VFS. It is assumed that the changes are equal.

The threshold value of the discriminator 108 is set to a value (for example, half value) equal to or less than the output of the amplifier 107 when the wavelength of each channel entering the wavelength tunable filter 103 from the transmission line matches the wavelength of the wavelength tunable filter 103. Set. H if the input signal is above the threshold value, L otherwise.
(H indicates a digital signal of 1 and L indicates a digital signal of 0).

The optical switch 110 has one input and two outputs, and when the optical switch control voltage VS is H, outputs the optical signal from the optical modulator 109 to the transmission line (hereinafter, this state is referred to as "transmission line side"). If the optical switch control voltage VS is L, the optical signal from the optical modulator 109 is output to the optical combiner 111 (hereinafter, this state is referred to as the “optical combiner side”). With this configuration, the wavelength tunable LD1 can be used without sending light to the transmission line side.
02 wavelength setting can be performed.

The optical combiner 111 joins the optical signal from the optical switch 110 and the optical signal from the transmission line and inputs them into the wavelength tunable filter 103.

FIG. 7 is an explanatory diagram of operations 1 to 4 of the wavelength control system when this optical transmitter is used. The wavelength is plotted along the horizontal axis, and the wavelength arrangement in each operation is shown. In the figure, the wavelength of the wavelength tunable LD 102 of the terminal station which is transmitting is shown by a vertical line, and the wavelength of the wavelength tunable filter is shown by a chevron. λL is the wavelength of the wavelength tunable LD 102, and λL_SS is the wavelength tunable LD 102.
Sweep start wavelength when sweeping, λL_SE is tunable LD1
02 is the sweep end wavelength during the sweep, λF is the wavelength of the tunable filter 103, λF_SS is the sweep start wavelength of the tunable filter 103, λF_SE is the sweep end wavelength of the tunable filter 103, λL_A is the adjacent wavelength, Δλ is the channel interval, dλ is a margin for ensuring the detection of the wavelength when the wavelength tunable filter 103 is swept or when the wavelength tunable LD 102 is swept. In the operation 1 of FIG. 7, the emission wavelength of the wavelength tunable LD 102 of the own station is set to λL, the sweep wavelengths of the wavelength tunable filter 103 are set to λF_SS to λF_SE, and the emission wavelength λL indicates a channel interval Δλ or less between adjacent wavelengths. . In operation 2, the emission wavelength λL is the channel interval Δλ or more. In the operation 3, the variable range of the emission wavelength of the variable wavelength LD is set to λL_SS to λL_SE, and the emission wavelength λL is almost equal to the adjacent wavelength λL_A in the channel interval Δλ.
Since it is in the vicinity, the emission wavelength λL satisfies the setting condition for the time being. In operation 4, the optical switch 110 is switched to the transmission path side, then the sweep range of the wavelength tunable filter 103 is narrowed to λF_SS to λF_SE, and the adjacent wavelength λ on the long wavelength side is set.
The emission wavelength of the wavelength tunable LD is controlled so that the wavelength interval with L_A is Δλ.

In this method, each optical transmitter 560 detects a usable wavelength range within the wavelength tunable range of the wavelength tunable LD using the wavelength tunable filter 103 at the start of light emission, and the available wavelength range is at the end of the wavelength range. The wavelength of the tunable LD 102 of another optical node is set as an adjacent wavelength, and light emission is started at a wavelength having a wavelength interval of Δλ. After that,
Wavelength tunable LD 10 by sweeping wavelength tunable filter 103
The wavelength interval between 2 and the adjacent wavelength is detected, and the wavelength interval is held in the channel interval Δλ. The adjacent wavelengths have finished communicating,
When the light emission is stopped, the adjacent wavelength is set as a new adjacent wavelength and the channel interval Δλ is held.

When there is no wavelength of another optical node within the wavelength tunable range of the wavelength tunable LD 102 at the start of light emission, or when the end of the wavelength tunable range of the wavelength tunable LD 102 is reached during the wavelength spacing maintaining operation, the wavelength is changed. The control state (for example, regarding injection current and temperature) of the wavelength tunable LD 102 at the end of the variable range is maintained.

By operating each optical transmitter 560 as described above, the wavelength arrangement of this wavelength division multiplexing communication system is
As shown in the schematic diagram of the wavelength arrangement of the operation 4 of FIG. 7, a group of several channels is formed in which the wavelength interval of adjacent channels is held at Δλ (in the example of FIG. 7, the number of channels is 12, the number of groups is 12). Is three).

[0021]

However, the optical transmitter used in the above-mentioned wavelength control system has the following problems.

The performance required for the wavelength tunable LD 102 used in the above-mentioned optical transmitter 560 is that it has a wide wavelength tunable range and the optical output intensity is within a certain range within the wavelength tunable range. Further, the wavelength tunable LD 102 when the wavelength is tunable
It is also necessary that the control of the injection current of is not complicated.

However, in a normal wavelength tunable LD, the wavelength tunable range in which the optical output intensity can be kept within a certain range is narrower than the limit value of the wavelength tunable range of the device. Electronics Letter
Magazine, Vol. 28, No. 11, pp. 1057-1058, "Two-segment mul"
tiquantum well lasers with 7nm tuning range and na
The wavelength tunable range according to the DFB-LD example described in “rrow linewidth” is 7.2 nm when the optical output change is kept within 2.5 dB, whereas the optical output intensity change is kept at 1 dB. In the case, it is 4.1 nm.

An object of the present invention is to maximize the use of the variable wavelength range of the variable wavelength LD and reduce the difference in the optical output intensity of the optical transmitters that emit light in the optical multiplex communication system. .

[0025]

In order to solve the above problems, the present invention detects the wavelength of the wavelength tunable light source and the wavelength on the transmission line by sweeping the wavelengths of the wavelength tunable light source and the wavelength tunable filter. A wavelength detecting means is provided, and the wavelength of the variable wavelength light source is set to a constant wavelength interval from one wavelength on the transmission path based on the wavelength detection result by the wavelength detecting means, and thereafter the constant wavelength interval is maintained. In the optical transmitter for a wavelength division multiplexing optical communication system for controlling the wavelength of the wavelength tunable light source, a light intensity adjusting means and a light intensity monitoring means for increasing or decreasing the optical output of the wavelength tunable light source are provided, and the light on the transmission line is The light intensity of the optical output of the transmitter is controlled to be the same as the light intensity of the adjacent wavelength.

Further, in the present invention, in the optical transmitter, when the wavelength of the wavelength tunable light source is set to a fixed wavelength interval from one wavelength on the transmission line, the optical output of the wavelength tunable light source is set on the transmission line. In order to carry out without outputting, a one-input, two-output optical switch that switches the output destination of the optical output of the wavelength tunable light source between the transmission line and the wavelength detecting means, and the light from the transmission line and the tunable light source An optical combiner for merging optical outputs and inputting them to the wavelength detecting means, wherein the optical output of the variable wavelength light source is inputted to the wavelength detecting means via a transmission line, and the wavelength without the transmission line. In order to reduce the light intensity difference of the optical output of the variable wavelength light source when being input to the detection means, one output of the optical switch may be input to the optical combiner via the optical attenuator.

Further, in the present invention, in the optical transmitter, an optical branching device for outputting the optical output of the wavelength tunable light source to the wavelength detecting means and the transmission line, and the optical output of the wavelength tunable light source. ON / OFF the output to the wavelength detection means
In some cases, an optical switch for turning it off is provided, and the optical output of the wavelength variable light source from the optical branching device is output to the transmission line via the light intensity adjusting means.

Further, in the optical transmitter control method of the present invention, the optical transmitter is configured so that the wavelength of the wavelength tunable light source is set at a constant wavelength interval from one wavelength on the transmission line based on the wavelength detection result by the wavelength detecting means. The wavelength of the variable wavelength light source is controlled so as to maintain the constant wavelength interval, and the optical intensity of the optical output of the optical transmitter on the transmission path is made equal to the optical intensity of the adjacent wavelength. Control to be.

[Operation] According to the invention of the present application, the optical output intensity of the optical transmitter can be made constant over the entire wavelength tunable range of the wavelength tunable LD, and light is emitted in the communication system. The difference in the optical output intensity of the optical transmitter can be reduced.

[0030]

Embodiments of the present invention will be described below in detail with reference to the drawings.

[First Embodiment] In the present embodiment, the light output intensity of the optical transmitter is adjusted by the light amount adjusting means such as an optical amplifier so that the light intensity becomes the same as the adjacent wavelength. The comparison of the light intensity with the adjacent wavelength is performed by the transmitted light intensity of the wavelength tunable filter obtained when the wavelength tunable filter for wavelength arrangement detection is swept.

The first embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of a first embodiment of an optical transmitter according to the present invention. As shown in the figure, the present optical transmitter includes a wavelength control system 101, a wavelength tunable LD 102, a wavelength tunable wavelength tunable filter 103, a wavelength tunable LD drive circuit 104, a wavelength tunable filter drive circuit 105, a light receiving element 106, and an amplifier 10.
7, discriminator 108, optical modulator 109, optical switch 11
0, an optical combiner 111, an optical amplifier 112, an optical amplifier drive circuit 113, and an optical attenuator 114. Note that there are the following four points in the configuration from the conventional example of the optical transmitter, and the description of the common blocks will be omitted. (1) The optical amplifier 112 is arranged between the wavelength tunable LD 102 and the optical modulator 109. (2) The wavelength control system 10 including the optical amplifier drive circuit 113
The control is performed by the optical amplifier control voltage VA from 1. (3) The output of the amplifier 107 is not only input to the discriminator 108 but also to the wavelength control system 101 as the light intensity monitoring voltage VM. (4) The optical attenuator 114 and the optical switch 110 and the optical combiner 1
It is placed between 11.

As the optical amplifier 112, a semiconductor type or an optical fiber type is at a practical level. The semiconductor-type optical amplifier allows a normal laser diode to function as an amplifier by applying a bias current below a threshold value.
nGaAsP surface type optical amplifier, photoexcitation surface type optical amplifier, semiconductor optical amplifier having axial taper active layer, GaAs / G
Like an aAlAs.ITG laser, it has the same structure as an LD and can be integrated with the wavelength tunable LD 102. In this embodiment, a semiconductor optical amplifier is used. In the semiconductor type optical amplifier, a low reflection film is formed on the end face of the LD, and the injection current is used below the oscillation threshold, and its amplification factor can be controlled by the injection current.

The optical amplifier drive circuit 113 includes the wavelength control system 1
Optical amplifier control voltage from 01 (hereinafter referred to as "VA")
The optical amplifier 112 is driven so that the amplification factor corresponds to

The optical attenuator 114 is for reducing the optical intensity difference between the wavelengths of its own station when the optical switch 110 is connected to the transmission line side and the optical combiner side. Optical switch 11
When 0 is connected to the transmission line side, as shown in FIG.
Since the star coupler 530 distributes the light intensity of each station to each of the optical fibers 551 to 554, the star coupler 5
Attenuates by the number of branches of 30. On the other hand, when the optical switch 110 is connected to the optical combiner side, the optical intensity of the wavelength of the own station is directly input to the optical combiner 111. In order to minimize the difference in the optical intensities of the wavelengths of the own station input to the optical combiner 111 in these two states, the optical attenuator 114 attenuates the optical intensity when the optical switch 110 is on the optical combiner side.

FIG. 2 is an explanatory view of the wavelength control operation when the optical transmitter 560 of this embodiment is used. With the wavelength as the horizontal axis, the wavelength arrangement in each operation is shown by the vertical line. Further, in order to show how the optical output intensity of the optical transmitter 560 is adjusted by the optical amplifier 112, the length of the vertical line is roughly corresponding to the minimum optical output intensity. Then, in order to show how the optical output intensity of the optical transmitter 560 is increased by the optical amplifier 112, the wavelength tunable LD among the optical output intensity of the optical transmitter 560 is shown.
The output of 102 is shown by a solid line, and the increase by the optical amplifier 112 is shown by a dotted line. Other symbols in the drawings such as λL are the same as those in FIG. 7. The operations are from operation 1 to operation 4. Check the wavelength range available in operation 1 and operation 2,
In operation 3, the wavelength of the wavelength tunable LD 102 of the own station is set to the position of Δλ and the wavelength of another station at the end of the wavelength arrangement (then, becomes the adjacent wavelength of this station), and in operation 4, the adjacent wavelength λ is set.
The tunable LD 102 on the short wavelength side by Δλ with respect to L_A
Maintain the wavelength of.

The following operation is performed by the wavelength control system 101 using each component of the optical transmitter 560.

(A) Operation 1 In operations 1 and 2, the wavelength tunable range of the wavelength tunable LD 102 of its own station and the available wavelength range (not interfering with the wavelengths of other stations) in it are obtained. In operation 1, the wavelength tunable LD 102 of the local station is caused to emit light at the shortest wavelength in the wavelength tunable range, and the wavelength arrangement is checked.

Therefore, the optical switch 110 is set to the side of the optical combiner (to prevent interference with other wavelengths), and the wavelength tunable LD1 is used.
02 is the control voltage VL = VL_MIN and the shortest wavelength (λ
L_MIN), and the wavelength tunable filter control voltage VF is swept from VF_MIN to VF_MAX with the optical amplifier 112 as the maximum amplification factor (to enable detection even when the optical output intensity of the wavelength tunable LD 102 is small).
The wavelength of the tunable filter 103 is set to λF_MIN to λF_.
Sweep to MAX. The output of the discriminator 108 during the sweep
VF that has become H ″ is VF_M1-n (n = 1, 2,
...) (in the example of the figure, 1 including the wavelength of the own station)
Since there are two wavelengths, VF_M1-1 to VF_M1-
12 are stored).

(B) Operation 2 In operation 2, the wavelength tunable LD 102 of its own station is caused to emit light at the longest wavelength in the wavelength tunable range, and the wavelength arrangement is examined.

For this reason, the optical switch 110 is on the optical combiner side (to prevent interference with other wavelengths), and the wavelength tunable LD1 is used.
02, the variable wavelength LD control voltage VL = VL_MAX is set to emit light at the longest wavelength (λL_MAX), and the optical amplifier 112
Is the maximum amplification factor (to enable detection even when the optical output intensity of the wavelength tunable LD 102 is small), and the wavelength tunable filter control voltage VF is set to VF_MIN to VF_MAX.
The wavelength of the wavelength tunable filter 103 by λF_MI.
Sweep from N to λF_MAX. The wavelength control system 101 is
The VF at which the output of the discriminator 108 becomes “H” during the sweep is V
It is stored as F_M2-n (n = 1, 2, ...) (In the example of the figure, since there are 12 wavelengths including the wavelength of the own station, VF_M2-1 to VF_M2-12 are stored).

After the sweep is completed, the control voltages VF_M1-1 to VF_M1-n of the wavelength tunable filter 103 and the wavelengths VF_M2-1 to VF_M2-n of the wavelength tunable filter 103 are compared to determine the wavelength of the wavelength tunable LD 102 of the own station. A variable range and a usable wavelength range (which does not interfere with the wavelengths of other stations) within the variable range are obtained.

(C) Operation 3 The wavelength tunable LD of the own station is located at one of the ends of the usable wavelength range (in the example of the figure, a wavelength on the short wavelength side of Δλ + dλ of λL_A).
The wavelength of 102 is set.

For this reason, the optical switch 110 is on the side of the optical combiner (to prevent interference with other wavelengths), and the tunable filter 103 has (a) VF = VF_LA- (ΔVF + dVF) when the adjacent wavelength is on the long wavelength side. (Here, VF_LA is the adjacent wavelength λL_A, and dV is d.
(corresponding to λ), the wavelength is set to λL_A- (Δλ + dλ), and (b) when the adjacent wavelength is on the short wavelength side, VF
= Λ_A + as VF_LA + (ΔVF + dVF)
The wavelength is set to (Δλ + dλ), and the optical amplifier 11
2 is the maximum amplification factor (so that it can be detected even when the optical output intensity of the wavelength tunable LD 102 is small), the control voltage VL of the wavelength tunable LD 102 is swept from VL_MIN, and the output of the discriminator 108 is "H". The sweep is stopped when the value becomes, and the control voltage VL of the variable wavelength LD 102 is fixed. (D) Operation 4 The wavelength λL of the tunable LD 102 of the local station and the adjacent wavelength λL_
The distance from A is set to Δλ, and the optical output intensity of the optical transmitter 560 of the own station is set to be the same as the optical output intensity of the adjacent wavelength λL_A.

Therefore, the optical switch 110 is on the transmission line side, and the tunable filter 103 (a) sweeps from VF_L-dVF to VF_L + ΔVF + dVF when the adjacent wavelength is on the long wavelength side, and sweeps wavelength from λL-dλ to λL + Δλ + dλ, (B) When the adjacent wavelength is on the short wavelength side, sweep from VF_L + dVF to VF_L- (ΔVF + dVF), the wavelength is λL + dλ to λL- (Δλ + dλ)
As the sweeping, the wavelength tunable LD 102 and the optical amplifier 112 are controlled based on the information obtained by the sweeping of the wavelength tunable filter 103.

At the time of sweeping the wavelength tunable filter 103 in this operation, the output of the discriminator 108 becomes "H" twice. At the first time, the wavelength of the wavelength tunable filter 103 is the wavelength tunable L of the own station.
When it matches the wavelength λL of D102, the second time is when the wavelength λL_A of the tunable filter 103 matches the adjacent wavelength. VF at these times is VF_M4-1, VF_
As M4-2, the light intensity monitoring voltage VM is VM_M4-
1 and stored as VM_M4-2. The adjacent wavelength λ
When L_A ends the transmission and stops the light emission, VF_M4 is set even at the end of the sweep of the wavelength tunable filter 103.
-2, VM_M4-2 is not stored. Then VF
_M4-2 is VF at the end of the wavelength tunable filter sweep
Is stored. Further, the value in the previous operation 4 is held as VM_M4-2.

The wavelength control of the wavelength tunable LD 102 is performed so as to separate from the adjacent wavelength when | (VF_M4-1)-(VF_M4-2) | is smaller than ΔVF. When the adjacent wavelength is on the long wavelength side, VL is reduced to shift the wavelength to the short wavelength side, and when the adjacent wavelength is on the short wavelength side, VL is shifted to the long wavelength side.
To increase.

On the other hand, in the wavelength control of the wavelength tunable LD 102, when | (VF_M4-1)-(VF_M4-2) | is larger than ΔVF, control is performed so as to approach the adjacent wavelength.

When the adjacent wavelength is on the long wavelength side, VL is increased to shift the wavelength to the short wavelength side, and when the adjacent wavelength is on the short wavelength side, VL is shifted to shift the wavelength to the long wavelength side. Make it smaller.

The amplification factor control of the optical amplifier 112 is VM_M.
4-1 is made equal to VM_M4-2.
When VM_M4-1 is smaller than VM_M4-2, the control voltage VA to the optical amplifier 112 is increased to increase the amplification factor of the optical amplifier and increase the optical output intensity. VM_M4-1
Is larger than VM_M4-2, the optical amplifier control voltage VA is reduced to lower the amplification factor of the optical amplifier and the optical output intensity is reduced.

The operation 4 is repeated, and the wavelength of the local station is controlled so that the interval with the adjacent wavelength becomes a constant wavelength interval Δλ, and the light intensity is controlled to be equal to the light intensity of the adjacent wavelength.

When no wavelength other than the wavelength of the own station is detected in the detection of the wavelength arrangement at the start of light emission, or while the operation 4 is repeated, the wavelength tunable LD 10 of the own station is detected.
When reaching one end of the wavelength tunable range of 2, there is no adjacent wavelength that serves as a reference for the optical output intensity. In these cases, with the optical switch 110 on the transmission path side, the wavelength of the wavelength tunable filter 103 is set to the wavelength tunable LD 10 of the own station.
When the wavelength of 2 matches, the output of the discriminator 108 is "
The amplification factor of the optical amplifier 112 is adjusted so as to be “H”, and the settings of the wavelength variable LD drive circuit 104 and the optical amplifier drive circuit 113 are held constant.

[Second Embodiment] FIG. 3 is a block diagram of a second embodiment of an optical transmitter 560 of the present invention. As shown in the figure, the present optical transmitter includes a wavelength control system 101 and a wavelength tunable LD 1.
02, wavelength tunable wavelength tunable filter 103, wavelength tunable LD
Drive circuit 104, wavelength tunable filter drive circuit 105, light receiving element 106, amplifier 107, discriminator 108, optical modulator 109, optical switch 302, optical combiner 111, optical amplifier 112, optical amplifier drive circuit 113, optical branching device 301 It is composed of It should be noted that blocks having the same reference numerals as those in FIGS. 1 and 6 are the same as those in the respective drawings, and thus detailed description thereof will be omitted.

FIG. 1 showing the configuration of the optical transmitter of the first embodiment.
There are the following four differences. (1) The optical output of the optical modulator 109 is divided into two by the optical branching device 301. The branching ratio of the optical branching device 301 is variable wavelength L
When the wavelength of the wavelength tunable filter 103 coincides with the wavelength of the smallest optical output intensity in the wavelength tunable range of D102, the optical amplifier 112 is in a range where the condition is satisfied so that the output of the discriminator 108 becomes "H". Set so that the side branching ratio is as large as possible. (2) The optical amplifier 112 is arranged between one output port of the optical branching device 301 and the transmission line. By setting the amplification factor of the optical amplifier 112 to 0, the wavelength of the wavelength tunable LD 102 can be set at a position Δλ from the adjacent wavelength without outputting the optical output of the wavelength tunable LD 102 to the transmission line. (3) Optical switch 3 with ON / OFF type optical switch 302
ON / OFF of the optical output of 01 to the optical coupler 111 is controlled. (4) There is no optical attenuator.

FIG. 4 is an explanatory diagram of the wavelength control operation when the optical transmitter 560 of this embodiment is used. Optical amplifier 11
2, the operation of the optical switch (ON / OFF type) 302, and the same as FIG. 2, which is an operation explanatory diagram of the first embodiment, except for the light intensity of the wavelength of the own station in operation 1, operation 2, and operation 3. Is. In operation 1, operation 2, and operation 3, the wavelength of the own station is not amplified by setting the amplification factor of the optical amplifier 112 to 0, and therefore is represented only by the solid line. Further, the path from the wavelength tunable LD 102 to the light receiving element 106 is also shown. Therefore, the light intensity is also different.

The operation performed by the wavelength control system 101 is as follows.
Optical switch (ON / OFF type) 302 and optical amplifier 112
Since it is the same except for the above, the operation of each of these two components will be described.

In operation 1, operation 2 and operation 3, the optical switch (ON / OFF type) 302 is controlled to be in the ON state, and the optical output of the wavelength tunable LD 102 is output to the optical combiner 111. The optical amplifier 112 has an amplification factor set to 0 under the control of the optical amplifier drive circuit 113, and the wavelength tunable LD 102
The optical output of is not output to the transmission line.

In operation 4, the optical switch (ON / OFF
The type) 302 is controlled to be in an OFF state so that the optical output of the wavelength tunable LD 102 is not output to the optical combiner 112. The optical amplifier 112 is controlled so as to have the maximum amplification factor in the first operation 4, and in the operation 4 repeated thereafter, the optical amplifier driving circuit 113 of the optical amplifier drive circuit 113 is controlled so that the optical input intensity of the adjacent wavelength becomes the same as that of the own station. The amplification rate is controlled by the control.

[Other Embodiments] As the configuration of the optical transmitter, it is possible to adopt another configuration in which the light intensity of the optical output of the wavelength tunable LD can be adjusted by the light amount adjusting means.

In the above embodiment, the optical amplifier is used as the light quantity adjusting means, but other means such as an optical attenuator may be used. In this case, the tunable LD 109
It is preferable that the light source output level is sufficiently high.

Further, as the operation of the optical transmitter, the wavelength of the wavelength tunable LD of the own station is held at the position of Δλ from the adjacent wavelength,
It is also possible to replace it with another operation that can keep the light intensity the same. For example, the wavelength sweep of the wavelength tunable filter may be performed from the long wavelength side to the short wavelength side, or the initial setting of the amplification factor of the optical amplifier may be set to a specific value instead of the maximum or zero.
In addition, the present invention is not limited to the above-mentioned operation, but can be widely used.

[0063]

As described above, according to the invention of the present application, the optical output intensity of the optical transmitter can be made constant over the entire wavelength tunable range of the wavelength tunable LD. Further, since the control of the optical output intensity is performed on the basis of the adjacent wavelengths, the optical output intensity of the adjacent channel is the same as that of the wavelength tunable LD and the detailed characteristics of the amplification factor of the optical amplifier are not required. You can

As a result, the usable wavelength range can be widened and the channel interval margin can be reduced. Therefore, when the wavelength tunable LD having the same characteristics is used, the number of channels can be increased.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of an optical transmitter of the present invention.

FIG. 2 is an explanatory diagram of a wavelength control operation when the first embodiment of the optical transmitter of the present invention is used.

FIG. 3 is a configuration diagram of a second embodiment of an optical transmitter of the present invention.

FIG. 4 is an explanatory diagram of a wavelength control operation when the second embodiment of the optical transmitter of the present invention is used.

FIG. 5 is a configuration diagram of an optical communication system.

FIG. 6 is a configuration diagram of a conventional example of an optical transmitter.

FIG. 7 is an explanatory diagram of a wavelength control operation when a conventional example of an optical transmitter is used.

[Explanation of symbols]

 101 wavelength control system 102 wavelength tunable LD 103 wavelength tunable filter 104 wavelength tunable LD drive circuit 105 wavelength tunable filter drive circuit 106 light receiving element 107 amplifier 108 discriminator 109 optical modulator 110 optical switch (1 input, 2 output) 111 optical combiner 112 optical amplifier 113 optical amplifier drive circuit 114 optical attenuator 301 optical brancher 302 optical switch (ON / OFF) 511-514 terminal station 521-524 optical node 530 star coupler 541-544 optical fiber 551-554 optical fiber 560 optical transmission 570 Optical receiver 580 Optical splitter

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04B 10/04 10/06

Claims (7)

[Claims] 1. A wavelength tunable light source, and wavelength detection means for detecting the wavelength of the wavelength tunable light source and the wavelength on the transmission line by sweeping the wavelength of the wavelength tunable filter, and the wavelength detection result by the wavelength detection means is provided. Based on the above, the wavelength of the variable wavelength light source is set to a fixed wavelength interval from one wavelength on the transmission path, and thereafter, the wavelength of the variable wavelength light source is controlled so as to maintain the constant wavelength interval. In the optical transmitter for use, a light intensity adjusting means and a light intensity monitoring means for increasing or decreasing the light output of the wavelength tunable light source are provided, and the light intensity of the light output of the tunable light source on the transmission line is adjusted to the light of the adjacent wavelength. An optical transmitter characterized by being controlled to be equal to the intensity. 2. When the wavelength of the variable wavelength light source is set to a constant wavelength interval from one wavelength on the transmission line, the wavelength variable light source outputs light without being output on the transmission line. A one-input, two-output optical switch that switches the output destination of the optical output of the wavelength tunable light source to the transmission line and the wavelength detecting means, and merges the light from the transmission line and the optical output of the wavelength tunable light source, An optical transmitter comprising: an optical combiner for inputting to the wavelength detecting means, wherein the optical output of the wavelength tunable light source is input to the wavelength detecting means via the transmission line, and without passing through the transmission line. In order to reduce the light intensity difference of the optical output of the wavelength tunable light source when it is input to the wavelength detection means, one of the optical switches is provided.
The optical transmitter according to claim 1, wherein two outputs are input to the optical combiner via an optical attenuator. 3. An optical branching device for outputting the optical output of the variable wavelength light source to the wavelength detecting means and the transmission line, and an optical output of the variable wavelength light source to the wavelength detecting means.
The optical switch for turning on / off the optical output of the wavelength tunable light source from the optical branching device is output to the transmission line via the light intensity adjusting means. Optical transmitter. 4. The method of controlling an optical transmitter according to claim 1, 2, or 3, wherein the wavelength of the variable wavelength light source is changed from one wavelength on a transmission line based on a wavelength detection result by the wavelength detection means. The wavelength of the variable wavelength light source is controlled so as to maintain the constant wavelength interval, and the light intensity of the optical output of the variable wavelength light source on the transmission line is adjacent to the adjacent wavelengths. A method for controlling an optical transmitter, wherein the optical intensity is controlled to be equal to the optical intensity of the optical transmitter. 5. A variable wavelength light source capable of varying the wavelength of the light source,
A wavelength tunable filter capable of varying the transmission wavelength, and a wavelength control system capable of controlling the wavelength tunable light source and the wavelength tunable filter are provided, and the output of the wavelength tunable light source is sent to a transmission line to change the wavelength on the transmission line. An output of the wavelength tunable filter, wherein the output of the wavelength tunable filter is swept to control the output wavelength of the wavelength tunable light source at a constant interval with the wavelengths of other optical transmitters on the transmission line. Detection means for detecting the detection level of the wavelength tunable light source and the detection level of the wavelength of the other optical transmitter by detecting the level, and detecting the wavelength tunable light source by controlling the output level of the wavelength tunable light source An optical transmitter comprising a control means for controlling the level and the detection level of the wavelength of the other optical transmitter to fall within a predetermined range. 6. The optical transmitter according to claim 5, wherein the detection means detects the output of the wavelength tunable filter via the photoelectric conversion means at the electric signal level, and the control means is the electric signal. An optical transmitter comprising level adjusting means for comparing a level with a level of an adjacent wavelength and increasing or decreasing an output level of the wavelength tunable light source. 7. The optical transmitter according to claim 6, wherein the level adjusting means includes an amplifier for amplifying an output of the wavelength tunable light source, and the amplifier is amplified by a control signal from the wavelength control system. The optical transmitter is characterized in that the control means is included in the wavelength control system.