KR100211583B1 - The stabilizing system of laser diode for wavelength division multiplexing - Google Patents

Abstract

The present invention relates to a light source stabilization system for a light transmission system using wavelength division multiplexing,

The system includes N light source stabilizers 100 including a laser diode LD as a light source; An Nx1 mux (MUX: 400) for combining the N optical signals output from the light source stabilizer; A 1 × 2 coupler 500 for detecting a portion of the transmission signal; An optical etalon filter 600 in which the detected signal for light source stabilization is tuned to specified frequencies; A photo detector (PD) 700 for converting the optical signal output from the optical etalon filter 600 into an electrical signal; An amplifier 800 for amplifying the converted electrical signal,

The light source stabilizer 100 is:

The fixed frequency oscillator 101 oscillated at an integer multiple of the sine wave frequency to be obtained, the frequency divider 102 for obtaining its specified sine wave frequency from the square wave oscillation frequency of the fixed frequency oscillator 101, and high frequency components are removed. A differential amplifier 105 for amplifying a difference value between the S1 and S2 signals input as the low pass filter 103 for obtaining its own sinusoidal wave, and the temperature initial value 104 initialized with the mode selection switch 200, and A current converter 106 for converting a voltage signal into a current, a laser diode 109 for outputting a sine wave having a specified frequency among 1 to N specified frequencies, and a sine wave and current from the low frequency filter 103. As a mixer 110 for modulating the bias current (LD bias) in the laser diode 109 using the output from the converter 113, and as the current initial value 111 initialized by the mode selection switch 200. A differential amplifier 112 for amplifying a difference value between the inputted S5 and S6 signals, a current converter 113 for converting a voltage signal into a current signal, and the temperature initial value 104 and a current in a system initialization state, respectively. Switches 107 and 114 connected to the differential amplifiers 105 and 112 so as to input an initial value 111, and to level converters R1 108 and R2 115, respectively, in a system normal state, and output signals of the amplifier 800; A level detector 119 for detecting its own sinusoidal signal, a differential amplifier 117 for generating the error signal by inputting a sinusoidal signal detected from the level detector 119 and a reference value 118, and An error controller 116 for converting the error signal into a control signal, a mode selection switch 200 for determining the initial state and the normal state of the system, and a temperature adjustment signal generated by each of the first and second feedback loops ( Provide a time difference between S3) and the current adjustment signal S7. And characterized by comprising a delay unit 201 is not assigned.

Description

Light Source Stabilization System for Wavelength Division Multiplexing Optical Transmission System

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light source stabilization system for a wavelength division multiplexing (WDM) optical transmission system. In particular, the present invention relates to a stable light source by automatically eliminating frequency shift using a stabilizer of laser diode. A light source stabilization system for a wavelength division multiplexed optical transmission system that generates a desired light output at a frequency.

The wavelength division multiplexing optical transmission system refers to a system that can greatly increase transmission capacity per optical fiber by multiplexing multiple transmission lasers having different wavelengths into one optical fiber.

Therefore, transmission lasers in optical transmission systems using wavelength division multiplexing must operate at specific internationally standardized frequencies. Therefore, in order to satisfy such an optical transmission system, the wavelength of the transmission laser must be precisely adjusted at the production plant or installation site of the system. In addition, the transmitting lasers must be managed to operate at the standard frequency for the life of the system.

However, even though the operating frequency of the laser is kept constant, the frequency of the laser may be tens of GHz or more due to the aging effect. Such a shift of the laser frequency has a problem that the reliability of data communication is deteriorated, such as reducing the gain margin of the wavelength division multiplex optical transmission system or causing a crosstalk of a signal, thereby causing communication failure.

Accordingly, the present invention is to overcome this problem, the transmission lasers are automatically operated at the standard frequency and generate the desired light output by using a light source stabilizer composed of a simple H / W to eliminate the frequency shift phenomenon as described above A light source stabilization system for a wavelength division multiplexing optical transmission system is adjusted.

1 is an overall configuration diagram of a light source stabilization system.

2 is a block diagram of a light source stabilizer.

3 is a level detector configuration diagram.

4 is an error controller 1 configuration diagram.

5 is an error controller 2 configuration diagram.

6 is an error controller 3 configuration diagram.

7 is an optical spectral diagram of a transmission characteristic curve of an optical etalon filter

* Explanation of symbols for main parts of the drawings

100: N light source stabilizers 400: Nx1 mux

500: 2x1 Coupler 600: Photo Etalon Filter

700: photodiode 800: amplifier

101: fixed frequency oscillator 102: divider

103,123: low pass filter 104: initial temperature

105,112,117: differential amplifier 106,113: current transducer

107,114 switch 109 laser diode

110: mixer 111: initial current value

116: error controller 117: differential amplifier

118: reference value 119: level detector

120: amplifier 121,125: buffer amplifier

122,126 multiplier 127 loop filter

128: voltage controlled oscillator 129: divider

130,135,140: Integrator 131,136,141: Differentiator

132,142: level comparator 133,146: switch 134,139,144: adder

R1: 108, R2: 115, R3: 137, R4: 138, R5: 143, R6: 145: level shifter

200: mode selection switch

In order to achieve the above object, the present invention, the N light source stabilizer (100) including a laser diode (LD) as a light source; An Nx1 mux (MUX: 400) for combining the N optical signals output from the light source stabilizer 100; A 1 × 2 coupler 500 for detecting a portion of the transmission signal; An optical etalon filter 600 in which the detected signal for light source stabilization is tuned to specified frequencies; A photo detector (PD) 700 for converting the optical signal output from the optical etalon filter 600 into an electrical signal; An amplifier 800 for amplifying the converted electrical signal,

The light source stabilizer 100 may include: a fixed frequency oscillator 101 oscillated at an integer multiple of a sine wave frequency to be obtained, and a divider for obtaining a specified sine wave frequency from a square wave oscillation frequency of the fixed frequency oscillator 101 ( 102, a low pass filter 103 for removing high frequency components to obtain a sine wave, and an amplification difference between the S1 and S2 signals input as the temperature initial value 104 initialized by the mode selection switch 200, respectively. A differential amplifier 105, a current converter 106 for converting a voltage signal into a current, a laser diode 109 for outputting a sine wave having one of a specified frequency from 1 to N, and the low pass filter 103 The mixer 110 modulates a bias current (LD bias) in the laser diode 109 by using a sinusoidal wave from and the output from the current converter 113, and is initialized by the mode selector switch 200. A differential amplifier 112 for amplifying the difference between the S5 and S6 signals input as the preset value 111, a current converter 113 for converting a voltage signal into a current signal, and the temperature initial values in a system initialization state, respectively. A switch 107 and 114 connected to the differential amplifiers 105 and 112 to input the 104 and the current initial value 111, respectively, and to the respective level converters R1: 108 and R2: 115 in a system normal state; A differential amplifier for inputting the level detector 119 for detecting the sinusoidal signal of the output signal of the 800, the sinusoidal signal detected from the level detector 119 and the reference value 118, and generating the error signal. 117, an error controller 116 for converting the error signal into a control signal, a mode selection switch 200 for determining the initial state of the system and the normal state of the system, and first and second feedback loops. Generated temperature adjustment signal S3 and current adjustment signal S7 That the given time difference, or consists of a delay unit 201 does not give characterized.

Hereinafter, with reference to the accompanying drawings will be described in more detail the configuration of the present invention.

1 is an overall configuration diagram showing a light source stabilization system of the present invention.

As shown, the light source stabilization system of the present invention includes N light source stabilizers 100 and N light emitted from the light source stabilizer 100, each of which includes a laser diode LD as a light source and is identically configured. Nx1 mux 400 for combining the signal, 1x2 coupler 500 for detecting a portion of the transmission signal, and the optical etalon filter 600 in which the detected signal for light source stabilization is tuned to the specified frequencies as shown in FIG. ), A photo detector (PD) 700 for converting the optical signal output from the optical etalon filter 600 into an electrical signal, and an amplifier 800 for amplifying the converted electrical signal.

FIG. 2 is a detailed configuration diagram of one light source stabilizer 100 among the N light source stabilizers 100 shown in FIG. 1.

As shown in Fig. 2, each of the light source stabilizers 100 is designated from a fixed frequency oscillator 101 and a square wave oscillation frequency of the fixed frequency oscillator 101 oscillated at an integer multiple of the sine wave frequency to be obtained. A frequency divider 102 for obtaining its sinusoidal frequency, a low pass filter 103 for removing high frequency components to obtain a sinusoidal frequency, and a temperature initial value 104 initialized with the mode selection switch 200, respectively. A differential amplifier 105 for amplifying the difference between the S1 and S2 signals, a current converter 106 for converting the voltage signal into a current, and a laser diode for outputting a sine wave having one of specified frequencies from 1 to N ( 109, a mixer 110 for modulating a bias current (LD bias) in the laser diode 109 using the sinusoidal wave from the low pass filter 103 and the output from the current converter 113, and mother A differential amplifier 112 for amplifying a difference value between the S5 and S6 signals inputted as the current initial value 111 initialized by the selection switch 200, a current converter 113 for converting a voltage signal into a current signal, and The differential amplifiers 105 and 112 are respectively connected to input the temperature initial value 104 and the current initial value 111 in the system initialization state, and to the level converters R1: 108 and R2: 115 in the system normal state, respectively. A level detector 119 for detecting the switches 107 and 114 to be connected, an output signal of the amplifier 800 of FIG. 1, and a sinusoidal signal and a reference value 118 detected from the level detector 119. A differential amplifier 117 for generating an error signal that is a difference value between the sinusoidal signal and the reference value 118 as an input, and an error controller (Proportion, Integration Differetiation (PID): 116) for converting the error signal into a control signal. Determine the initial state and normal state of the system Is configured to include a mode selection switch 200 and the first and second temperature adjustment signal and the delay unit 201 is not assigned a time difference, or grant the current control signal by the feedback loop.

In this case, modulation of the bias current LD bias in the laser diode 109 may be performed at an input part or an output part of the laser diode 109.

3 is a detailed block diagram of the level detector 119 shown in FIG.

As shown, the level detector 119 is an amplifier 120 to which the output signal of the amplifier 800 of FIG. 1 is input, and a buffer amplifier 121 to which the output signal of the amplifier 120 is separately input. And 125), and an output signal of the buffer amplifier 125 passes in order to distinguish its signal, and is composed of a multiplier 126, a loop filter 127, a voltage regulating generator 128, and a divider 129. And a multiplier 122 and a low pass filter 123 in which the output signal of the buffer amplifier 121 detects and outputs only its current signal size with the help of the voltage adjusting oscillator 128. do.

4 is an error controller configuration diagram 1 showing the error controller 116 shown in FIG. 2 in more detail.

As illustrated, the error controller 116 includes an integrator 130, a differentiator 131, and a level comparator 132 to which an error signal, which is an output signal of the differential amplifier 117 of FIG. 2, is input. And a switch 133 adjusted by the level comparator 132, and an adder 134 whose input signal is determined by the switch 133 and outputs a control signal.

FIG. 5 is a diagram illustrating a configuration of an error controller in FIG. 4.

As shown, the error controller 116 includes an integrator 135 and a differentiator 136 to which the error signal, which is an output signal of the differential amplifier 117 of FIG. 2, is input, and the integrator 135 and the differentiator, respectively. The level converters R3: 137 and R4: 138 to which the output signals of 136 are respectively input, and their input signals are determined by the level converters R3: 137 and R4: 138, and output control signals. The adder 139 is comprised.

FIG. 6 is an error controller configuration diagram illustrating a state in which FIG. 4 and FIG. 5 are combined.

As illustrated, the error controller 116 may include an integrator 140, a differentiator 141 and a level comparator 142 to which an error signal, which is an output signal of the differential amplifier 117 of FIG. 2, is input, respectively, and an integrator ( 140 and the level converters R5: 143 and R6: 145 to which the output signals of the differentiator 142 are input, respectively, and their input signals are the level converters R5: 143 and R6: 145 and the level comparator 142, respectively. And an adder 144 for outputting a control signal.

The light source stabilization system of the present invention is operated by being divided into two modes, a system initialization state and a system normal state, by using the mode selection switch 200 and the retarder 201 of FIG. 2 driven by a user.

Hereinafter, the operation principle of the present invention with reference to the accompanying drawings.

First, the operation in the system initialization state of the present invention will be described.

In the system initialization state, among the components of the light source stabilization system shown in FIG. 1, only N light source stabilizers 100 including the laser diode LD as a light source and each identically configured are driven for light source stabilization. The Nx1 mux 400, the 1x2 coupler 500, the photo etalon filter 600, the photo detector 700, and the amplifier 800, which are external detection means for stabilization, do not operate during system initialization for light source stabilization.

In addition, only some components of FIG. 2, which are detailed configurations of the light source stabilizer 100, operate in the system initialization state.

This will be described in more detail as follows.

First, the system initialization state is determined by the mode selection switch 200.

In the system initialization state, the switch 107 and the switch 114 are connected to the differential amplifiers 105 and 112, respectively, to input the temperature initial value 104 and the current initial value 111, respectively.

The temperature initial value 104 is generated by receiving a fixed voltage value and a thermistor (THM) value in the laser diode 109, and is generated in the laser diode 109 through the differential amplifier 105 and the current converter 106. Turn on the Thermo-Electric Cooler (TEC).

As the temperature initial value 104 for adjusting the thermoelectric cooler TEC, S1 and S2 are used.

S1 is generated by receiving the fixed reference voltage value and the thermistor (THM) value in the laser diode 109, and S2 is connected to S4 through the switch 107. This S2 is an initial voltage value for matching the initial frequency of the laser diode 109 to a specified frequency, and is a value that can vary from laser diode 109 to each other.

The reason for generating the temperature initial value 104 by returning the thermistor (THM) value in the laser diode 109 as described above is that the laser diode 109 has a shortened life due to an impact caused by overcurrent at the time of system initialization. To stabilize the operation of the laser diode 109.

This temperature initial value 104 passes through a differential amplifier 105 for amplifying the difference between the two input signal values S1 and S2 and through a current converter 106 for converting the voltage signal into a current signal. The thermoelectric cooler (TEC) in 109 is operated.

For reference, a characteristic of a general laser diode is that as the temperature increases, a resistance value, which is a thermistor value in the laser diode, decreases, and a temperature increase effect occurs when the current value applied to the thermoelectric cooler in the laser diode increases.

Due to this temperature rise, the frequency of the laser diode 109 is lowered (or the wavelength is increased), but the power value of the laser diode 109 is also changed due to the adjustment of the thermoelectric cooler (TEC).

In addition, the current initial value 111 is generated by receiving the fixed voltage value and the photodetector PD value in the laser diode 109, and the mixer 110 through the differential amplifier 112 and the current converter 113. In addition to the sine wave generated from the low-pass filter 103 to adjust the bias current (LD bias) in the laser diode 109.

S5 and S6 are used as the current initial value 111 for adjusting the bias current (LD bias) in the laser diode 109.

S5 is generated by receiving a precisely fixed reference voltage value and a photo detector PD value in the laser diode 109, and S6 is connected to S8 through a switch 114. This S6 is an initial voltage value for matching the initial power of the light source to the specified power, and is a value that can be changed for each laser diode 109.

The reason for generating the current initial value 111 by returning the photodetector PD value as described above is to prevent the laser diode 109 from shortening its life due to an impact caused by an overcurrent at the time of initializing the system. This is to stabilize the operation of 109).

The initial current value 111 is passed through the differential amplifier 112 for amplifying the difference between the two input signal values S5 and S6 and through the current converter 113 for converting the voltage signal into a current signal 110. ) Is added to the sine wave which is the output signal of the low pass filter 103 to adjust the bias current LD bias in the laser diode 109.

For reference, the characteristic of the general laser diode is that the power increases as the bias current in the laser diode increases, and the frequency also changes due to the bias current adjustment in the laser diode.

Now, the operation in the system steady state will be described.

In the system steady state, all components of the light source stabilization system shown in FIG. 1 are driven, which will be described below.

Each of the N light source stabilizers 100 includes a laser diode 109 which is a light source; A laser adjusting unit including an initial value (104, 111), differential amplifiers (105, 112, 117), current converters (106, 113), an error controller (116), a reference value (118), and a level detector (119); It consists of a low frequency sinusoidal wave generator comprising a fixed frequency oscillator 101, a divider 102 and a low pass filter 103.

By using a bias current (LD bias) of the laser diode 109 to modulate a low frequency sine wave, the optical frequency is dithered to a low frequency range.

That is, the bias current LD bias is a means for distinguishing each channel corresponding to each laser diode 109.

In this way, the N optical signals are modulated and output from the N light source stabilizers 100 into sinusoids having different N low frequencies, and the Nx1 mux for combining the N optical signals modulated into the sinusoidal waves and output. 400 and 1x2 coupler 500 for detecting a portion of the transmission signal for light source stabilization.

In this case, the modulation of the laser diode 109 may be performed at an input part or an output part of the laser diode 109, and the sine wave that modulates the laser diode 109 affects the data carried on the laser diode 109. The size should be very small so that no

The signal detected for light source stabilization passes through the optical etalon filter 600 tuned to the designated frequencies (or wavelengths) as shown in FIG. 7, where the optical signal output from the optical etalon filter 600 is tuned. N wavelengths are lambda 1, lambda 2, ..., lambda 2, and the wavelength spacing of each channel is constant at ?? / 2.

The output of the optical etalon filter 600 passes through the optical detector 700 which converts the optical signal into an electrical signal, and the optical signal having a very high frequency is eliminated, and the low frequency of shaking the optical frequency in the low frequency range is removed. Only sinusoids remain.

As a result, an electrical signal is output, which is the sum of the low frequency sinusoids.

Therefore, when the N sinusoids output from the light source stabilizer 100 have a lowest frequency of K, the highest frequency must be lower than 2 x K to distinguish their sinusoids.

Since the electrical signal output from the photo detector 700 has a very small signal size, the level detector 119 of the light source stabilizer 100 shown in FIG. 2 through an amplifier 800 for amplifying the electrical signal. Is entered.

Now, the operation of the light source stabilizer 100 operating in the system steady state will be described with reference to FIG.

After the system initialization state is completed, in the system normal state, the switch 107 and the switch 114 are connected to the level converters R1: 108 and R2: 115, respectively.

In the stabilization loop for stabilizing the light source in the system steady state, the output signal of the amplifier 800 of FIG. 1 passes through the level detector 119 for detecting its sine wave size, and amplifies the difference from the reference value 118. An error signal is generated through the differential amplifier 117.

The error signal includes the output of the level detector 119 having its current sinusoidal signal size, and the differential amplifier 117 having a reference value 118 having the maximum sinusoidal signal size at a specified frequency and power condition. It means the signal inputted by) and the difference value is outputted.

The error signal output from the differential amplifier 117 is converted into a control signal after passing through the error controller 116.

This control signal is connected to each of the level converters R1: 108 and R2: 115 to adjust the thermoelectric cooler TEC and the bias current LD bias in the laser diode 109 through the same path as the system initialization state.

The laser diode 109, which is a light source, outputs an optical signal having one of the specified frequencies (or wavelengths) from 1 to N.

As described above, the sinusoidal wave for channel classification uses the bias current of the laser diode 109 to modulate the low frequency sinusoidal wave to shake the optical frequency in a low frequency range.

The sine wave for channel classification includes a fixed frequency oscillator 101 oscillated at an integer multiple of the sine wave frequency to be obtained, a divider 102 for obtaining its own frequency, and a low pass filter for obtaining a sine wave by removing high frequency components ( It is generated via a sine wave generator consisting of 103).

Here, the frequency of the sine wave generated through the sine wave generator is a frequency band of several hundreds of KHz.

When generating a sine wave from the low-pass filter 103 in the sine wave generator, it is preferable to oscillate at a high frequency that is an integer multiple of the input signal frequency in consideration of conditions such as the size of the high frequency oscillator 101 in the sine wave generator.

As described above, the sine wave signal, which is the AC signal generated from the low filter 103, is mixed in the DC signal of the current converter 113 and the (AC) mixer 110, and modulates the bias current of each laser diode 109 and is incidental. This can also reduce the effects of stimulated Brillouin Scattering.

The system normal state, which is an operating state after the system initialization, is also determined by the mode selection switch 200, and the switch 107 and the switch 114 are for the S3 signal and the current adjustment, which are feedback values for temperature adjustment, respectively. It is connected to differential amplifiers 105 and 112, respectively, so that the feedback value S7 signal is input.

At this time, the temperature adjustment by the first feedback loop is for operating the laser diode 109 at a specified frequency, and the current adjustment by the second feedback loop is for maintaining the power of the laser diode 109 at a specified level. .

At this time, the delay unit 201 provides a time difference between the temperature adjustment signal S3 and the current adjustment signal S7 to adjust the power after adjusting the wavelength of the laser diode 109 first in the normal state of the system.

The wavelength and power of the laser diode 109 may be simultaneously adjusted by removing the retarder 201 or zeroing the delay time, which is the time difference between the temperature adjustment signal S3 and the current adjustment signal S7.

The input signal of the light source stabilizer 100 for stabilizing the light source in the system steady state is the output signal of the amplifier 800 of FIG. In the end, the electrical signal, the combined form of sinusoids with low frequencies, was amplified.

Here, when the optical etalon filter 600 is stably configured, if each sinusoidal signal of the N sinusoidal signals outputted from the laser diode LD is located at the peak value of the optical etalon filter 600 which is a designated wavelength, The sine wave size of must be detected at each light source stabilizer (100). This is because its sine wave size means the degree of stabilization of each laser diode LD.

Therefore, to pass through the level detectors 119 included in the N light source stabilizers 100 to detect their sinusoidal magnitudes.

Referring to FIG. 3, the operation of the system steady state with respect to the level detector 119 of FIG. 2 is as follows.

Since the input signal of the level detector 119 which is the output signal of the amplifier 800 of FIG. 1 is connected to the level detectors 119 included in the N light source stabilizers 100, it passes through the amplifier 120 again. It is separated into a buffer amplifier 121 for detecting its sinusoidal signal size and another buffer amplifier 125 for distinguishing its sinusoidal signal.

The signal passing through the buffer amplifier 125 passes through a phase locked loop for ignoring sinusoidal signals of other channels among the N sinusoidal signals output from the laser diode 109 and distinguishing sinusoidal signals of its own. do.

The phase-locked loop includes a multiplier 126 serving as a phase difference detector, a loop filter 127 for removing high frequency components, a voltage adjusting oscillator 128 adjusted to be in phase with an input signal, and the voltage adjusting oscillator ( And a divider 129 for making the oscillation frequency from 128 into a specified sinusoidal frequency.

Through this process, a sinusoidal signal having the same frequency and phase as its sinusoidal signal is generated.

The input signal of the multiplier 122, which is a path for detecting the magnitude of its sinusoidal signal, is one of N mixed sinusoids that are output signals of the buffer amplifier 121 and N sinusoids that are output signals of the divider 129. A signal synchronized with its own sinusoidal wave is input, respectively, and a product signal is output.

The product signal is detected by the low pass filter 123 and output only its current sinusoidal signal size, and the remaining high frequency components are removed.

The operations of FIGS. 4, 5, and 6 illustrating various changeable configurations of the error controller (PID) 116 illustrated in FIG. 2 are as follows.

In FIG. 4 showing the error controller 1, an error signal that is an output signal of the differential amplifier 117 of FIG. 1 is input to the integrator 130, the differentiator 131, and the level comparator 132, respectively. Here, the integrator 130 is to remove the error value that is the difference between the output value of the level detector 119 and the reference value 118, the time is required to stabilize the slow response, the differentiator 131 is fast response speed It has the characteristics to improve the copper characteristic.

This property was used in the present invention.

At the beginning of the system steady state, the input signal of the level comparator 132 is generally small compared to the reference value in the level comparator 132 so that the switch 133 is shorted.

Accordingly, since the integral value and the derivative value, which are the output values of the integrator 130 and the differentiator 131, are reflected in the input signal of the adder 134, a control signal is generated in which the response speed rapidly reduces the error.

When the laser diode 109 is relatively stabilized by the control signal after a certain time, the switch 133 is opened because the input signal of the level comparator 132 is larger than the reference value in the level comparator 132.

Therefore, the adder 134 reflects only the integral value and generates a control signal to accurately reduce the error.

Thus, the use of the level comparator 132 and the switch 133 can improve the dynamic characteristics and at the same time reduce the error.

5 shows an error controller 2, in which the error signal is input to the integrator 135 and the differentiator 136 as a variant of FIG. 4, and an input signal of the adder 139 is interposed between the integrator 135 and the adder 139. The reflection ratio of the integral value and the derivative value is determined by the conversion ratio of the arranged level converters R3: 137 and the conversion ratio of the level converters R4: 138 arranged between the differentiator 136 and the adder 139.

Accordingly, the adder 139 reflects the integral value and the derivative value whose reflection ratio is determined by the level converter R4: 138, and generates a control signal to accurately reduce the error.

In this way, the use of the level converters R3: 137 and R4: 138 can accurately reduce errors while improving dynamic characteristics.

6, which shows an error controller 3, will be described as a combination of the error controller 1 and the error controller 2 as follows.

The error signal is input to the integrator 140, the differentiator 141, and the level comparator 142.

At the beginning of the steady state of the system, the input signal of the level comparator 142 is generally small compared to the reference value in the level comparator 142 so that the switch 146 is shorted.

Accordingly, since the integral value and the derivative value whose reflection ratios are determined by the level converter R5: 143 and the level converter R6: 145 are reflected in the input signal of the adder 144, the response speed rapidly reduces the error. Signal is generated.

When the laser diode 109 is relatively stabilized due to the control signal after a certain time, the switch 146 is opened because the input signal of the level comparator 142 is larger than the reference value in the level comparator 142.

Therefore, only the integral value is reflected in the adder 144. The control signal is generated to accurately reduce the error.

As such, the use of the level comparator 142, the switch 146, and the level converters R5: 143 and R6: 145 can improve the dynamic characteristics and reduce the error accurately.

Looking at the operation of the light source stabilizer 100 of Figure 2 in the normal system state as follows.

The control signal output from the error controller PID 116 is simultaneously input to the level converter R1 108 for temperature adjustment and the level converter R2 115 for current adjustment. The level converters R1: 108 and R2: 115 are converted in consideration of adjustment characteristics of the laser diode 109, that is, offset and change width.

In order to adjust the thermoelectric cooler THM of the laser diode 109, the signal from the temperature initial value 104, which is S1, and the output value of the level converter R1: 108, which is a shorted S3 signal at S4, are used.

At this time, S1 receives the thermistor (THM) value in the laser diode 109 with the same signal used in the system initialization state, and generates the initial temperature value 104.

Here, the reason why the S1 signal is used is to prevent the laser diode 109 from shortening its life due to the shock caused by overcurrent at the initial stage of the system steady state and to stabilize the operation of the light source.

The S1 and S3 signals pass through a differential amplifier 105 to amplify the difference between these two signals, and the thermoelectric cooler TEC in the laser diode 109 is adjusted to a bias current LD bias, thereby adjusting the adjusted voltage signal. The thermoelectric cooler (THM) is adjusted via a current converter (106) for conversion into a current signal.

In addition, in order to adjust the bias current LD bias in the laser diode 109, the signal from the current initial value 111 of S5 and the output value of the level converter R2: 115, which is the S7 signal shorted to S8, are used. .

At this time, S5 receives the photodetector PD value with the same signal used in the system initialization state and generates the current initial value 111.

The reason for using the S5 signal is to prevent the laser diode 109 from shortening its life due to an overcurrent shock at the beginning of the system steady state and to stabilize the operation of the light source.

The S5 and S6 signals pass through the differential amplifier 112 to amplify the difference between these two signals, and since the bias current (LD bias) in the laser diode 109 cannot be adjusted to voltage, the adjusted voltage signal is converted into a current signal. The bias current LD bias is adjusted via a current converter 113 for conversion.

The current converters 106 and 107 for adjusting the thermoelectric cooler THM and the bias current LD in the light source protect the light source by not exceeding the maximum variable current capacity with reference to the characteristics of the laser diode.

The structural features of the present invention described above are as follows.

A. The present invention employs a light source stabilizer 100 that can be implemented with a simple H / W only so that a laser diode as a light source automatically generates a desired light output at a designated frequency in a light transmission system using wavelength division multiplexing.

N. The mode for stabilizing the light source is divided into system initialization state and system normal state.

C. Adjustment of the thermoelectric cooler (TEC) in the laser diode 109 is performed by returning the reference value 118 and the thermistor (THM) value in the laser diode 109 in the system initialization state so that the laser diode 109 can be used at the time of system initialization. It prevents the lifespan from being shortened by the shock caused by overcurrent and stabilizes the operation of the light source.

In addition, even when the system is in a normal state, the feedback value using the light source stabilization loop and the thermistor (THM) value in the laser diode 109 are used to prevent the laser diode 109 from shortening its life due to the shock caused by overcurrent at the system initialization time. The operation of the light source was stabilized.

D. The adjustment of the bias current (LD bias) in the laser diode 109 is performed by returning the reference value and the photodetector PD value, which is a photodiode in the laser diode 109, from the system initialization state so that the laser diode 109 initializes the system. It prevents the lifespan from being shortened by the impact of overcurrent at the time and stabilized the operation of the light source.

In addition, even when the system is in a steady state, the feedback value using the light source stabilization loop and the photodetector (PD) value of the photodiode in the laser diode 109 are fed back and used, so that the laser diode 109 may be damaged due to the impact caused by the overcurrent at the system initialization time. This shortening was prevented and the operation of the light source was stabilized.

M. In an optical transmission system using wavelength division multiplexing, a signal for modulating a channel corresponding to each light source for light source stabilization is modulated into a sine wave having different low frequencies by using a bias current (LD bias) of the laser diode 109. .

As a means of detecting only sinusoidal signals of mixed sinusoids for light source stabilization, instead of band pass filter which is easy to deteriorate and frequency band must be changed for each optical transmission system, it is possible to accurately distinguish one's own signal. A phase locked loop constituting the frequency detector or the level detector 119 constituted in the same manner was used.

Iii. The error controller 116 for generating a control signal at the error value is shown as integrators 130, 135, 140, differentiators 131, 136, 141, level converters (R3: 137, R4: 138, R5: 143, R6) as shown in Figs. It is possible to improve the dynamic characteristics, which are the response speed, and to generate a control signal to accurately reduce errors.

Due to the above configuration features, the light source automatically generates a desired light output at a stable frequency

A) increase the number of channels in a wavelength division multiplex optical transmission system;

B) Reliable data communication can be realized by eliminating frequency transition.

Claims (19)

N light source stabilizers 100 including a laser diode LD as a light source; An Nx1 mux (MUX: 400) for combining the N optical signals output from the light source stabilizer 100; A 1 × 2 coupler 500 for detecting a portion of the transmission signal; An optical etalon filter 600 in which the detected signal for light source stabilization is tuned to specified frequencies; A photo detector (PD) 700 for converting the optical signal output from the optical etalon filter 600 into an electrical signal; From the photo detector 700 to the amplifier 800 for amplifying the converted electrical signal Done, The light source stabilizer 100 is: A fixed frequency oscillator 101 oscillated at an integer multiple of the sine wave frequency to be obtained, A divider 102 for obtaining its specified sinusoidal frequency from the square wave oscillation frequency of the fixed frequency oscillator 101, A low pass filter 103 for removing a high frequency component to obtain its sinusoidal frequency; A differential amplifier 105 for amplifying a difference value between the S1 and S2 signals inputted as the temperature initial value 104 initialized by the mode selection switch 200; A current converter 106 for converting a voltage signal into a current; A laser diode 109 for outputting a sine wave having one of a specified frequencies from 1 to N, A mixer 110 for modulating a bias current (LD bias) in the laser diode 109 by using a sine wave from the low filter 103 and an output from the current converter 113, A differential amplifier 112 for amplifying a difference value between the S5 and S6 signals respectively input as the current initial value 111 initialized by the mode selection switch 200; A current converter 113 for converting a voltage signal into a current signal; Connected to the differential amplifiers 105 and 112 to input the temperature initial value 104 and the current initial value 111 in the system initialization state, and to the level converters R1: 108 and R2: 115 in the system normal state, respectively. With switches 107 and 114, An output signal of the amplifier 800, the level detector 119 for detecting its sinusoidal signal, A differential amplifier 117 for generating an error signal that is a difference between the sinusoidal signal and the reference value 118 by inputting the sinusoidal signal detected from the level detector 119 and the reference value 118; An error controller 116 for converting the error signal into a control signal; The mode selection switch 200 for determining an initial state and a normal state of the system; To the retarder 201 which does or does not give a time difference between the temperature adjustment signal S3 generated by the first feedback loop and the current adjustment signal S7 generated by the second feedback loop. Made up of, Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 1, wherein the mode selection switch 200 driven by the user is characterized in that the operation is divided into two modes, the system initialization state and the system normal state, Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 2, wherein in the system initialization state, only the N light source stabilizers 100 operate, In the normal state of the system, the N light source stabilizers 100, the Nx1 mux 400, the 1x2 coupler 500, the optical etalon filter 600, and the detector (PD: 700) And, characterized in that the amplifier 800 is operated, Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 1, wherein the first feedback loop includes the switch 107, the temperature initial value 104, the differential amplifier 105 and the current converter 106, The second feedback loop is characterized in that it comprises the switch 114, the current initial value 111, the differential amplifier 112 and the current converter 113, Light source stabilization system for wavelength division multiplex optical transmission system. The method according to claim 1, wherein if the retarder 201 gives a time difference between the temperature adjustment signal S3 and the current adjustment signal S7, The thermoelectric cooler TEC in the laser diode 109 is adjusted before the bias current LD bias in the laser diode 109 when the system initialization state is changed to a normal state. If the retarder 201 does not give a time difference between the temperature adjustment signal S3 and the current adjustment signal S7, Characterized in that the thermoelectric cooler (TEC) in the laser diode 109 and the bias current (LD bias) in the laser diode 109 are simultaneously adjusted when the system initialization state is changed to the normal state. Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 5, wherein the thermoelectric cooler (TEC) In the system initialization state, the fixed reference value and the thermistor (THM) value in the laser diode 109 are fed back and adjusted. In the normal state of the system, the feedback value generated through the first feedback loop and the thermistor (THM) value is characterized in that the feedback is adjusted, Light source stabilization system for wavelength division multiplex optical transmission system. The method according to claim 6, characterized in that the feedback value generated through the first feedback loop becomes an output value of the level converter R: 108 as the temperature adjustment signal S3. Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 5, wherein the bias current is, In the system initialization state, it is adjusted using a fixed reference value and the photodetector (PD) value in the laser diode 109, In the system steady state, it is adjusted using the feedback value generated through the second feedback loop and the photodetector (PD) value in the laser diode 109, Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 8, wherein the feedback value generated through the second feedback loop is an output value of the level converter R2: 115 as the current adjustment signal S7. Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 1, wherein the error controller 116, An integrator 130, a differentiator 131 and a level comparator 132 to which the error signal, which is an output signal of the differential amplifier 117, is input, and a switch 133 adjusted by the level comparator 132, Its input signal is determined by the switch 133, characterized in that it comprises an adder 134 for outputting a control signal, Light source stabilization system for wavelength division multiplex optical transmission system. The method according to claim 10, wherein the control signal output from the adder 134, When the switch 133 is shorted by the level comparator 132, the output value of the integrator 130 and the output value of the differentiator 131 are reflected to the input signal of the adder 134 and output. When the switch 133 is opened by the level comparator 132, only the output value of the integrator 130 is reflected to the input signal of the adder 134 and is output. Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 1, wherein the error controller 116, An integrator 135 and a differentiator 136 to which the error signal as an output signal of the differential amplifier 117 is input, and a level converter R3 to which an output signal of the integrator 135 and differentiator 136 is input, respectively; 137, R4: 138, and its input signal is determined by the level converters R3: 137, R4: 138, and includes an adder 139 for outputting a control signal. Light source stabilization system for wavelength division multiplex optical transmission system. The method according to claim 12, wherein the control signal output from the adder 139, The output value of the integrator 135 and the output value of the differentiator 136 are reflected to the input signal of the adder 139 at the conversion ratio of the level converter R3: 137 and the level converter R4: 138, respectively, and are outputted. Characterized by Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 1, wherein the error controller 116, The integrator 140, the differentiator 141, and the level comparator 142 to which the error signal, which is the output signal of the differential amplifier 117, is input, and the output signals of the integrator 140 and the differentiator 142, respectively, are input. The level converters R5: 143 and R6: 145 and their input signals are determined by the switch 146 which is controlled by the level converters R5: 143 and R6: 145 and the level comparator 142. Characterized in that it comprises an adder 144 for outputting a signal, Light source stabilization system for wavelength division multiplex optical transmission system. The method of claim 14, wherein the control signal output from the adder 144, When the switch 146 is shorted by the level comparator 142, the output value of the integrator 140 and the output value of the differentiator 141 convert the level converters R6: 145 and the level converters R5: 143, respectively. Is reflected to the input signal of the adder 144 at a ratio and outputted; When the switch 146 is opened by the level comparator 142, only the output value of the integrator 140 is reflected to the input signal of the adder 134 at the conversion ratio of the level converter R5: 143 and output. Characteristic, Light source stabilization system for wavelength division multiplex optical transmission system. The method according to any one of claims 10, 12 or 14, wherein the error signal Characterized in that the difference between the output value of the level detector 119 having a current sinusoidal signal size, and the reference value 118, respectively input to the differential amplifier 117, Light source stabilization system for wavelength division multiplex optical transmission system. The method according to claim 16, wherein the reference value 118 is characterized in that the laser diode 109 is the maximum sine wave size at a specified frequency and power situation, Light source stabilization system for wavelength division multiplex optical transmission system. The method according to claim 1, wherein the level detector 119, An amplifier 120 to which an output signal of the amplifier 800 is input; Buffer amplifiers 121 and 125 to which the output signal of the amplifier 120 is separated and input, respectively; The output signal of the buffer amplifier 125 passes to distinguish its own signal, and is a phase locked loop composed of a multiplier 126, a loop filter 127, a voltage regulator generator 128, a divider 129, A multiplier 122 in which the output signal of the buffer amplifier 121 and the signal passing through the phase-locked loop are input so that only its current signal size is detected and output; Characterized in that it comprises a low pass filter 123, Light source stabilization system for wavelength division multiplex optical transmission system. The signal output from the low-pass filter 123 is characterized in that, among the frequencies of the sine wave signal applied to the laser diode 109, when the lowest frequency is K, the highest frequency is 2K. Light source stabilization system for wavelength division multiplex optical transmission system.

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