CN101150369A - An optical transmitter circuit for restraining excited Brillouin scattering effect - Google Patents

Abstract

This invention relates to a light transmitter circuit for suppressing excited Brillouin dispersion effect including a drive circuit of a laser used in providing drive circuit to the laser, in which, optical signals generated by the laser is modulated by the modulator and transmitted, and the character of the transmitter circuit is that it includes a laser power output monitor module, a low frequency disturbing signal generating and amplitude modulating module and a coupling capacitor C, in which, the low frequency disturbing signal generating and amplitude regulating module includes a microprocessor, a D/A converting circuit, a square wave generating circuit and a low-pass filter circuit.

Description

A kind of optical transmitter circuit that suppresses the stimulated Brillouin scattering effect

Technical field

The present invention relates to optical sender, relate in particular to the optical transmitter circuit of a kind of inhibition stimulated Brillouin scattering (Stimulated Brillouin Scattering is hereinafter to be referred as SBS) effect.

Background technology

In the non-relay optical transmission system of long distance, need improve launched power as much as possible and come the compensated fiber loss, thus the Optical Signal To Noise Ratio of assurance receiving terminal.But, under higher launched power, the stimulated Brillouin scattering effect in the optical fiber can be transferred to the luminous power of fl transmission light signal rear orientation light and phonon fields, thereby causes a kind of loss mechanism of flashlight, cause the reducing of Optical Signal To Noise Ratio of receiving terminal, influence the performance of optical transmission system.The SBS effect is compared with the nonlinear effect (as from phase modulated, cross-phase modulation) in other several optical fiber, has minimum threshold power, generally only several milliwatts.Produce for fear of the SBS effect, system's launched power can only be limited in below the SBS threshold value, has so just limited the raising of signal launched power greatly.

In the prior art, can adopt the self phase modulation (Self-PhaseModulation of self channel, abbreviate SPM as), the cross-phase modulation effect (Cross-PhaseModulation abbreviates XPM as) of monitoring and controlling channels widens methods such as spectrum width and suppresses the SBS effect.But the inhibition of these methods is limited in one's ability, and might cause the wave distortion of signal.Also having a kind of method is to reduce the SBS effect by the additive phase modulator, and effect is pretty good, but cost is very high.Widen spectrum width by the modulation format of carrier suppressed in addition, but need change original transmitter module configuration to a great extent, realize complicated difficulty, cost is also very high.

Summary of the invention

The purpose of this invention is to provide a kind of optical transmitter circuit that suppresses the stimulated Brillouin scattering effect, be used at the non-relay optical transmission system of long distance, to reduce the influence of optical transmission system SBS effect.

In order to realize goal of the invention, technical scheme of the present invention is:

A kind of optical transmitter circuit that suppresses the stimulated Brillouin scattering effect, comprise drive circuit for laser, in order to provide drive current to laser, the light signal that this laser produces is through the laggard light inlet emission of modulators modulate, and the characteristics of this optical transmitter circuit are also to comprise laser power output monitoring modular, the generation of low-frequency excitation signal and amplitude adjusting module and coupling capacitance C.

Described laser power output monitoring modular is in order to the drive current of monitoring laser, its input links to each other with the output of described drive circuit for laser, in order to receive described drive current, the output of described laser power output monitoring modular produces with described low-frequency excitation signal and links to each other with the input of amplitude adjusting module, is used to provide monitor signal LsBIASMON;

Described low-frequency excitation signal produces with amplitude adjusting module and is used to produce the low-frequency excitation signal and adjusts its amplitude, its output links to each other with the input of described drive circuit for laser by described coupling capacitance C, be used to load this low-frequency excitation signal, thereby make the output spectra line broadening of described laser.

Described low-frequency excitation signal produces with amplitude adjusting module and comprises microprocessor, D/A converting circuit, square wave generation circuit and low-pass filter circuit.

Described microprocessor is used to determine the amplitude of low-frequency excitation signal and produces pulsewidth adjust signal, the input of this microprocessor is used to receive the monitor signal LsBIASMON of described laser power output monitoring modular output, through the amplitude of the described D/A converting circuit output low frequency disturbing signal input to described square wave generation circuit, the pulse width regulating circuit output pulse width of another output of this microprocessor through carrying adjusted signal another input to described square wave generation circuit to one output of this microprocessor by the synchronous parallel interface that carries.

Described square wave generation circuit comprises operational amplifier, analog switch, resistance R ₁, resistance R ₂And resistance R ₃, described resistance R ₁Cross-over connection between the output of the inverting input of described operational amplifier and described D/A converting circuit, described resistance R ₂Cross-over connection between the output of the in-phase input end of described operational amplifier and described D/A converting circuit, described R ₃Cross-over connection is between the inverting input and output of described operational amplifier, the output of the pulse width regulating circuit of the described microprocessor of input termination of described analog switch, controlled the switch of described analog switch selects by this pulse width regulating circuit, when this pulse width regulating circuit output high level, described operational amplifier in-phase input end and R ₂Ground connection, when this pulse width regulating circuit output low level, described operational amplifier in-phase input end and R ₂Directly be connected, the output of described operational amplifier links to each other with the input of described low-pass filter circuit, is used to export square wave.

Described low-pass filter circuit comprises resistance R ₄, resistance R ₅And capacitor C ₁, be used to filter the square wave that the input of this low-pass filter circuit receives, described resistance R ₄Cross-over connection between the output node of the output of described operational amplifier and described low-pass filter circuit, described resistance R ₅And capacitor C ₁Parallel connection, the output node of the described low-pass filter circuit of a termination, other end ground connection.

Laser power output monitoring modular is monitored the drive current of laser in real time, and monitoring result LsBIASMON is offered generation of low-frequency excitation signal and amplitude adjusting module.The low-frequency excitation signal produces with amplitude adjusting module and produces the low-frequency excitation signal, and the corresponding amplitude of adjusting disturbing signal of size of the laser drive current that arrives according to laser power output monitoring module monitors makes both ratios keep constant simultaneously.Disturbing signal is loaded on drive circuit for laser by coupling capacitance C, thereby makes the output spectra line broadening of laser.

According to the theory analysis of stimulated Brillouin scattering effect in the fiber optic transmission system, if light carrier cloth line broadening, under the situation of high bit rate, then the SBS threshold value will improve nearly one times.Therefore we can be applied to the low-frequency excitation signal on the direct current biasing point of light carrier laser, cause that light carrier laser linewidth widens, and then carry out data-modulated.This low-frequency excitation signal is a small-signal, and while in its cycle, its upper frequency limit satisfied the low-frequency cut-off frequency less than amplifier less than the transmission time of light signal in optical fiber.Under the small-signal modulation case, the live width final decision of laser optical spectrum peak place (is equivalent to modulation depth M in the peak value of the low-frequency excitation signal that applies _d).In optical transmission system, the Output optical power of laser need be regulated according to different demands, just its drive current is not a constant numerical value, therefore in order to guarantee that obtaining better SBS threshold value improves, the amplitude that needs to guarantee the low-frequency excitation signal changes with laser drive current.

Compared with prior art, beneficial effect of the present invention is as follows:

By the present invention, make the output spectra line broadening of laser, thereby reduced the influence of stimulated Brillouin scattering effect in the optical transmission system, particularly in the non-relay optical transmission system of long distance, reduced the influence of optical transmission system SBS effect.

Description of drawings

Fig. 1 is the block diagram that the present invention suppresses the optical transmitter circuit of SBS effect

Fig. 2 is the schematic diagram that the present invention suppresses the optical transmitter circuit of SBS effect

Embodiment

The present invention will be further described below in conjunction with drawings and Examples, but should not limit protection scope of the present invention with this.

See also Fig. 1, Fig. 1 is the block diagram that the present invention suppresses the optical transmitter circuit of SBS effect.This optical sender comprises laser 4, drive circuit for laser 1, laser power output monitoring modular 2, the low-frequency excitation signal produces and amplitude adjusting module 3, coupling capacitance C and modulator 5.Drive circuit for laser 1 provides dc bias current for laser 4, i.e. drive current, thus make laser produce light signal.This light signal is through the laggard light inlet emission of the modulation loading data of modulator 5 transmission.

The low-frequency excitation signal produces the generation circuit that comprises a low-frequency excitation signal with amplitude adjusting module 3.By the Output optical power of monitoring laser, the amplitude of this low-frequency excitation signal can change with laser drive current, is loaded on the drive circuit 1 of laser by coupling capacitance C then, light carrier is modulated, thereby caused the broadening of spectral line.

See also Fig. 2, Fig. 2 is the schematic diagram that the present invention suppresses the optical transmitter circuit of SBS effect.Laser output power monitoring modular 2 among Fig. 2 in the LsBIASMON corresponding diagram 1, remainder produces and amplitude adjusting module 3 corresponding to the low-frequency excitation signal.

The inner member of the low-frequency excitation signal generating circuit in generation of low-frequency excitation signal and the amplitude adjusting module 3 comprises:

I. microprocessor D1,4 power output monitor signal LsBIASMON adopt to laser, the amplitude of decision disturbing signal, and produce amplitude adjusted signal DitherTone.

Ii. by operational amplifier D3, resistance R ₁, resistance R ₂, resistance R ₃With the square wave generation circuit that analog switch SW1 forms, the amplitude Dither level that produces amplitude adjusted signal Dither Tone and the disturbing signal that is determined according to microprocessor D1 produces square wave.

Iii. by resistance R ₄, resistance R ₅And capacitor C ₁The low-pass filter circuit of forming filters out the HFS of square wave, exports adjusted low-frequency excitation signal V _Dither

Model crucial among Fig. 2 is as shown in table 1.

The tabulation of table 1 Primary Component

Item	The device model	Function
			D1	LPC2138	Microprocessor
D2	AD5328	D/A converting circuit
			D3	AD8605	Operational amplifier
SW1	MAX4624	Analog switch

LsBIASMON is laser 4 Output optical power monitor signals, is a voltage signal that is directly proportional with laser drive current.Microprocessor D1 monitors this signal by the analog to digital conversion circuit that carries, and determines the amplitude of low-frequency excitation signal thus.Because microprocessor output is digital signal, therefore carries out the amplitude Dither Level signal that digital-to-analogue conversion forms the low-frequency excitation signal by D/A converting circuit D2, this signal is finally controlled the amplitude of output disturbance signal.Carry out communication by SPI (synchronous parallel interface Synchronizationparallel interface) interface between microprocessor D1 and the D/A converting circuit D2.Operational amplifier D3 and gain of analog switch SW1 composition are+1 amplifier, and microprocessor D1 controls opening with closed of analog switch SW1 by the pulse width regulating circuit (PWM) that carries, thereby make square wave of operational amplifier D3 output.The amplitude of this square wave is by the amplitude Dither Level signal deciding of low-frequency excitation signal.

Being calculated as follows of low-frequency excitation signal amplitude:

V _level＝K _D(V _in-V _off)

In the formula, V _LevelExpression low-frequency excitation signal amplitude, V _InExpression laser power output monitoring modular 2 outputs to the monitor signal LsBIASMON of generation of low-frequency excitation signal and amplitude adjusting module 3, V _OffBe equivalent to by the caused laser Output optical power of laser threshold current monitor signal (being the amount that from LsBIASMON, to deduct according to the different manufacturers laser characteristic), V _Level, V _In, V _OffAll are magnitudes of voltage.K _DBe the coefficient of ratio that can be provided with according to actual different application systems, this coefficient need decide according to concrete drive circuit for laser.

According to communication protocol MSA 300Pin, the relation between laser Output optical power monitor signal LsBIASMON and the laser Output optical power monitor signal drive current is as follows:

$V_{\mathrm{in}}=20\frac{\mathrm{mV}}{\mathrm{mA}}{I}_{\mathrm{laser}}$

In the formula, I _LaserBe laser drive current, be threshold current I _ThresWith bias current I _BiasSum:

I _laser＝I _Bias+I _Thres

Therefore

$V_{\mathrm{in}}=20\frac{\mathrm{mV}}{\mathrm{mA}}(I_{\mathrm{Bias}}+I_{\mathrm{Thres}})$

If

$V_{\mathrm{off}}=20\frac{\mathrm{mV}}{\mathrm{mA}}{I}_{\mathrm{thres}}$

Then

$V_{\mathrm{level}}=20K_D\frac{\mathrm{mV}}{\mathrm{mA}}{I}_{\mathrm{Bias}}.$

The computational process of above-mentioned low-frequency excitation signal amplitude realizes by software coding, the burned microprocessor D1 of this program.

The above is preferred embodiment of the present invention only, is not to be used for limiting practical range of the present invention.Be that all equivalences of doing according to the content of the present patent application claim change and modification, all should be technology category of the present invention.

Claims (4)

1. optical transmitter circuit that suppresses the stimulated Brillouin scattering effect, comprise drive circuit for laser (1), in order to provide drive current to laser (4), the light signal that this laser (4) produces is characterized in that through the laggard light inlet emission of modulator (5) modulation this optical transmitter circuit comprises that also laser power output monitoring modular (2), low-frequency excitation signal produce and amplitude adjusting module (3) and coupling capacitance C;

Described laser power output monitoring modular (2) is in order to monitor the drive current of described laser (4), its input links to each other with the output of described drive circuit for laser (1), in order to receive the drive current of described laser (4), the output of described laser power output monitoring modular (2) produces with described low-frequency excitation signal and links to each other with the input of amplitude adjusting module (3), is used to provide monitor signal;

Described low-frequency excitation signal produces with amplitude adjusting module (3) and is used to produce the low-frequency excitation signal and adjusts its amplitude, its output links to each other with the input of described drive circuit for laser (1) by described coupling capacitance C, is used to load this low-frequency excitation signal.

2. the optical transmitter circuit of inhibition stimulated Brillouin scattering effect according to claim 1 is characterized in that described low-frequency excitation signal produces and amplitude adjusting module (3) comprises microprocessor (D1), D/A converting circuit (D2), square wave generation circuit and low-pass filter circuit;

Described microprocessor (D1) is used to determine the amplitude of low-frequency excitation signal and produces pulsewidth adjust signal, the input of this microprocessor (D1) is used to receive the monitor signal of described laser power output monitoring modular (2) output, through the amplitude of described D/A converting circuit (D2) the output low frequency disturbing signal input to described square wave generation circuit, the pulse width regulating circuit output pulse width of another output of this microprocessor (D1) through carrying adjusted signal another input to described square wave generation circuit to one output of this microprocessor (D1) by the synchronous parallel interface that carries;

The output of described square wave generation circuit links to each other with the input of described low-pass filter circuit, and the output of described low-pass filter circuit is used to export described low-frequency excitation signal.

3. the optical transmitter circuit of inhibition stimulated Brillouin scattering effect according to claim 2 is characterized in that described square wave generation circuit comprises operational amplifier (D3), analog switch (SW1), resistance R ₃And resistance R ₃, described resistance R ₁Cross-over connection between the output of the inverting input of described operational amplifier (D3) and described D/A converting circuit (D2), described resistance R ₂Cross-over connection between the output of the in-phase input end of described operational amplifier (D3) and described D/A converting circuit (D2), described R ₃Cross-over connection is between the inverting input and output of described operational amplifier (D3), the output of the pulse width regulating circuit of the described microprocessor of input termination (D1) of described analog switch (SW1), controlled the switch of described analog switch (SW1) selects by this pulse width regulating circuit, when this pulse width regulating circuit output high level, described operational amplifier (D3) in-phase input end and R ₂Ground connection, when this pulse width regulating circuit output low level, described operational amplifier (D3) in-phase input end and R ₂Directly be connected, the output of described operational amplifier (D3) links to each other with the input of described low-pass filter circuit, is used to export square wave.

4. the optical transmitter circuit of inhibition stimulated Brillouin scattering effect according to claim 2 is characterized in that described low-pass filter circuit comprises resistance R ₄, resistance R ₅And capacitor C ₁, be used to filter the square wave that the input of this low-pass filter circuit receives, described resistance R ₄Cross-over connection between the output node of the output of described operational amplifier (D3) and described low-pass filter circuit, described resistance R ₅And capacitor C ₁Parallel connection, the output node of the described low-pass filter circuit of a termination, other end ground connection.

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