CN103760732A - Cascade sum-frequency and difference-frequency all-optical wavelength converter and conversion method - Google Patents
Cascade sum-frequency and difference-frequency all-optical wavelength converter and conversion method Download PDFInfo
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Abstract
The invention discloses a cascade sum-frequency and difference-frequency all-optical wavelength converter and a conversion method. After second pump light of a second laser device of the converter is transmitted through a polarization controller, a linearly polarized light conversion device and a first optical coupler, the second pump light and signal light access a second optical coupler, an erbium-doped fiber amplifier and an optical circulator together and reach a PPLN (periodically poled lithium niobate) ridge waveguide, forward light beams are reflected by a Faraday 90-degree rotating reflector, backward light beams are transmitted into the ridge waveguide, and converted idler-frequency light is outputted from the optical circulator. The conversion method includes adjusting the pump light into a TM (transverse magnetic) mode by the polarization controller, and then converting the pump light into linearly polarized light by the online polarized light conversion device; decomposing the linearly polarized light into light in a TE (transverse electric) mode and light in a TM mode in the ridge waveguide; enabling the pump light in the TM mode and the signal light in a TM mode to perform cascade sum-frequency and difference-frequency reaction and generating the converted idler-frequency light in a TM mode; reflecting other forward light and converting a mode of the other forward light by the aid of the Faraday reflector; returning the other forward light to the ridge waveguide. The polarization direction of the linearly polarized light is parallel to the cross section of the PPLN ridge waveguide, and an angle theta is formed between the linearly polarized light and an X-axis. An amplitude ratio of the light in the TE mode to the light in the TM mode is tg theta. The cascade sum-frequency and difference-frequency all-optical wavelength converter and the conversion method have the advantage that wavelength conversion independent from a polarization state of the signal light can be implemented by the aid of the cascade sum-frequency and difference-frequency all-optical wavelength converter and the conversion method.
Description
Technical field
The invention belongs to optical communication technique field, a kind of cascade and frequency and difference frequency All Optical Wave Converter and conversion method have been specifically related to, be a kind of cascade based on PPLN optical waveguide and All Optical Wave Converter and the conversion method of frequency with difference frequency type, be mainly applicable to dense wave division multipurpose optical communication system.
Background technology
In optical communication technique field, need the data transmission of large capacity and two-forty.In optical fiber telecommunications system, dense wave division multipurpose (DWDM) can improve its transmission capacity especially significantly, and dense wave division multipurpose optical communication system is the technology that current development future is expected most.All Optical Wave Converter is one of critical nature device of dense wave division multipurpose optical communication network, All Optical Wave Converter realizes copying of the light carrier of information from the light carrier of a wavelength to another wavelength, contribute to wavelength recycling, effectively carry out dynamic routing selection, reduce network blocking probability, and then can improve dirigibility and the expandability of optical-fiber network, realize the forwarding of light signal in open dwdm system.
Conventional All-Optical Wavelength Conversion Techniques mainly comprises at present: XGM (XGM), Cross-phase Modulation (XPM), laser gain saturated absorption, electro-absorption modulation (EA), nonlinear optical loop mirror (NOLM), four-wave mixing (FWM), second order nonlinear effect etc.In existing scheme, based on periodically poled lithium niobate optical waveguide, All-Optical Wavelength Conversion Techniques referred to as PPLN optical waveguide, because the second order nonlinear effect of PPLN optical waveguide has unique superiority, as to strict transparent, multi-wavelength extremely low, the fast response time of transfer capability, mirror image wavelength conversion characteristic, noise figure simultaneously of signal bit rate and modulation format, and switching bandwith is very wide etc., thereby the All-Optical Wavelength Conversion Techniques based on PPLN optical waveguide is subject to various countries scientific worker's great attention in recent years.
At present aspect the wavelength conversion based on PPLN optical waveguide second order nonlinear effect, carrying out much significant work both at home and abroad, mainly comprise based on direct difference frequency (DFG), based on cascade frequency multiplication and difference frequency (SHG+DFG), based on cascade and frequently with the wavelength conversion technology of the second order such as difference frequency (SFG+DFG) and cascaded second-order nonlinear interaction.But these technology all exist defect.
Although DFG type All Optical Wave Converter conversion efficiency is higher, but because its pump light used (0.775 μ m) and flashlight (1.5 μ m) are in different-waveband, and differ greatly, DFG type All Optical Wave Converter is difficult to well pump light and flashlight are coupled into waveguide simultaneously, is difficult to realize pump light and the single mode transport of flashlight in optical waveguide simultaneously.
SHG+DFG type wavelength shifter based on cascade frequency multiplication and difference frequency has solved the difficulty that DFG type wavelength shifter runs into, and the pump light of injection and flashlight are in 1.5 mu m wavebands together, can realize the All Optical Wavelength Conversion of 1.5 mu m wavebands.But because pump light in cascade frequency multiplication and difference frequency process has occupied the wave band of flashlight, this is that a lot of dwdm systems institute is unallowed.And the pump light wavelength response bandwidth at the accurate phase matching of frequency multiplication (SHG) process (QPM) wavelength place is very narrow, flashlight for fixing input, traditional SHG+DFG type wavelength shifter is difficult to realize the tunable output of conversion ideler frequency light, and the conversion of tunable wavelength is very important for the dirigibility that strengthens network management.
Based on cascade with frequently can solve with the All Optical Wave Converter of difference frequency (SFG+DFG) problem that the SHG+DFG type wavelength shifter of DFG type and traditional cascade frequency multiplication and difference frequency runs into simultaneously.All incident lights are all in 1.5 mu m wavebands, even if also can realize easily tunable wavelength conversion for the flashlight of fixed wave length input on the other hand on the one hand.Based on cascade and frequency, there is Two-orders nonlinear effect with difference frequency (SFG+DFG), the first pump light and the second pumping light wavelength that are placed in the both sides of flashlight wave band window are similar to about the accurate phase matching wavelengths symmetry of frequency multiplication (SHG) process, and the first pumping light wavelength is λ
1, frequency is ω
1, the second pumping light wavelength is λ
2, frequency is ω
2.The close optimum coupling that easily realizes of pumping wavelength and signal wavelength again can Seize ACK message wave band.Regulate first, second pump light, the first pump light wavelength and the second pump light wavelength are met or be similar to accurate phase-matching condition satisfied and frequency (SFG) process, now first, second pump light occurs and (SFG) reaction frequently, generation and frequently light, and optical wavelength is λ frequently
sF, frequency is ω
sF, ω
sF=ω
p1+ ω
p2.Meanwhile, (wavelength is λ to flashlight
s, frequency is ω
s) (wavelength is λ with obtaining changing ideler frequency light with light generation difference frequency (DFG) interaction frequently
i, frequency is ω
i), ω
i=ω
sF-ω
s.According to conservation of energy principle, flashlight, the first pump light, the second pump light, and frequently light and conversion ideler frequency light wavelength meet following relational expression:
SFG:1/λ
SF=1/λ
p1+1/λ
p2
DFG:1/λ
i=1/λ
SF-1/λ
s
SFG+DFG：1/λ
i=1/λ
p1+1/λ
p2-1/λ
s
λ
p1---the first pumping light wavelength
λ
p2---the second pumping light wavelength
λ
s---signal light wavelength
λ
sF---and frequency light wavelength
λ
i---conversion ideler frequency light wavelength
But existing have polarization correlated based on cascade and frequency with the All Optical Wave Converter of difference frequency (SFG+DFG) type, when flashlight is inputted with polarization state, finally the conversion ideler frequency light intensity of output changes the variation with signal light polarization direction, thereby wavelength conversion efficiency is lower in the wavelength coverage of some.
Summary of the invention
The object of the present invention is to provide a kind of cascade and frequency and difference frequency All Optical Wave Converter, the PPLN optical waveguide of this All Optical Wave Converter is PPLN ridge waveguide, and be connected to linearly polarized light conversion equipment, simple in structure, conversion efficiency is higher, especially polarization independence performance is good, and can carry out fine tune.
Another object of the present invention is to provide a kind of cascade and the conversion method of frequency with difference frequency All Optical Wave Converter; inject PPLN ridge waveguide linear polarization pump light; in PPLN ridge waveguide, be decomposed into TM and TE mould; 90 ° of rotating mirrors of faraday make again the TE of flashlight and pump light and TM mould exchange and reflect; what make to participate in cascade and the pump light frequently react with difference frequency and flashlight can make up various losses in forward, backward transmission, and while making to export, the conversion efficiency of TE mould and TM mould is equal.
A kind of cascade of the present invention's design and frequency and difference frequency All Optical Wave Converter, comprise laser instrument, Polarization Controller, photo-coupler, Erbium-Doped Fiber Amplifier (EDFA), optoisolator, optical circulator, PPLN optical waveguide, 90 ° of rotating mirrors of faraday, the first laser instrument and second laser are tunable external cavity laser, the first pump light sending and the second pump light access respectively the first Polarization Controller and the second Polarization Controller, the output of the first Polarization Controller and the second Polarization Controller accesses after the first photo-coupler, access the second photo-coupler with together with flashlight through the random polarization state of Polarization Controller, the output access Erbium-Doped Fiber Amplifier (EDFA) of the second photo-coupler, the output of amplifier is through optoisolator access optical circulator the first port, the light beam of the fl transmission of optical circulator the second port output is after PPLN optical waveguide, light beam is reflected by 90 ° of rotating mirrors of faraday, the light beam of backward transmission enters again PPLN optical waveguide, the conversion ideler frequency light producing is output as the output of this wavelength shifter from the 3rd port of optical circulator.
Described the first pump light, the second pump light and flashlight are C-band.
Described the first pumping light wavelength is λ
p1, the second pumping light wavelength is λ
p2, this device produce with frequency optical wavelength be λ
sF, each wavelength meets: 1/ λ
sF=1/ λ
p1+ 1/ λ
p2.
The present invention's PPLN optical waveguide used is PPLN ridge waveguide, the substrate of this ridge waveguide is lithium niobate crystal chip, and ducting layer is that Z cuts period polarized zinc niobate lithium wafer, substrate and the ducting layer Direct Bonding of mixing, the square section of ridge waveguide is the XOY plane perpendicular to Z axis, is called Z tangent plane.PPLN ridge waveguide both can transmit TM mould, can transmit TE mould again, without with polarization beam apparatus, flashlight being divided into mutually orthogonal TE mould and TM mould, at output terminal, also without using polarization beam combiner that TE mould and the TM mould of conversion ideler frequency light is synthetic, reduce the complicacy of wavelength shifter.And PPLN ridge waveguide restricting signal light and pump light concentrate on transmission in waveguide, be conducive to improve conversion efficiency.
Respectively through first, second pump light tie-in line polarized light conversion device of the first Polarization Controller and the second Polarization Controller, then access the first photo-coupler.Linearly polarized light conversion equipment is converted to another kind of linearly polarized light the pump light of the TM pattern of directions X polarization, and the polarization direction of the linearly polarized light after conversion is parallel with the xsect (being Z tangent plane) of PPLN ridge waveguide, and with the vertical angled θ of X-axis.
Described linearly polarized light conversion equipment comprises the first faraday cell and the second faraday cell, principle based on faraday's magnetic rotation effect, magnetic opticity material in faraday cell makes the vibration plane of the linearly polarized light that passes through turn over certain angle under its magnetic fields, and the relational expression in the angle θ that the linearly polarized light vibration plane by faraday cell turns over and the magnetic field of faraday cell is:
θ=VBL
In formula, B is the magnetic induction density in faraday cell, and L is the length of magnetic opticity material, and V is scale-up factor Wei Erde constant, the temperature of V and magnetic opticity material, and character and lambda1-wavelength are relevant.
The first pump light of the present invention and the second pump light, enter respectively the first faraday cell and second faraday cell of linearly polarized light conversion equipment, respectively two pump lights carried out to the conversion of linearly polarized light, to improve the accuracy of linear polarization pump light conversion.
The polarization direction of the linear polarization pump light after described linearly polarized light conversion equipment conversion and vertical X-axis angulation θ, making TM mould and TE mode amplitude ratio that linear polarization pump light decomposes in PPLN ridge waveguide is 1 to 1.
Each accesses the first photo-coupler through polarization maintaining optical fibre the output of the first Polarization Controller and the second Polarization Controller, and Polarization Controller is combined to produce good pump light TM mould with polarization maintaining optical fibre.
On the optical fiber connecing at optical circulator the 3rd port, be connected to the first fiber grating and the second fiber grating, the reflectance spectrum centre wavelength of the first fiber grating and the second fiber grating is respectively the first pump light and the second pumping light wavelength.Non-switched pump light will be by the first fiber grating and the second fiber grating reflected light circulator, enter PPLN ridge waveguide again recycles, and improves the utilization factor of pump light, improves conversion efficiency.
A kind of cascade of the present invention and frequently as follows with the conversion method of difference frequency All Optical Wave Converter:
The first pump light that the first tunable laser and the second tunable laser are sent and the second pump light access respectively the first Polarization Controller and the second Polarization Controller, adjusting its polarization direction, making first, second pump light is TM mould, the output of the first Polarization Controller and the second Polarization Controller each through polarization maintaining optical fibre tie-in line polarized light conversion device, linearly polarized light conversion equipment the TM mould pump light of directions X polarization change into polarization direction and PPLN ridge waveguide transverse cross-section parallel and with the linearly polarized light of the angled θ of vertical direction X-axis.The linear polarization pump light of 2 kinds of wavelength after conversion is coupled by the second photo-coupler with together with flashlight through the random polarization state of Polarization Controller after the first photo-coupler, after amplifying through Erbium-Doped Fiber Amplifier (EDFA) again, the first port by optical circulator enters, from the second port of optical circulator, export, be coupled into for the first time simultaneously PPLN ridge waveguide, linear polarization pump light in PPLN ridge waveguide after conversion is decomposed into TE mould and TM mould, and the amplitude ratio of TE mould and TM mould equals tg θ.PPLN ridge waveguide transmits TM mould and TE mould simultaneously, and the now TM mould generation cascade of the TM mould of flashlight and pump light and frequency react, produce conversion ideler frequency light TM mould with difference frequency, and the TE mould of flashlight does not participate in cascade and frequently reacts with difference frequency in fl transmission process.The ideler frequency light TM mould that PPLN ridge waveguide produces, flashlight TE mould and pump light TE mould continue transmission forward, arrive 90 ° of rotating mirrors of faraday.90 ° of rotating mirrors of described faraday, make flashlight, and 90 ° of rotations occur for pump light and conversion ideler frequency polarisation of light state, complete the mutual conversion between two kinds of patterns of TE and TM and make it and reflect, return and carry out backward transmission.The ideler frequency light TM mould producing when the rotary reflection of 90 ° of rotating mirrors of faraday makes fl transmission changes the TE mould that TE mould, flashlight TE mould change TM mould, linear polarization pump light into into and changes TM mould into, and transfer backward transmission to and enter PPLN ridge waveguide, the TM mould of flashlight new transition reacts with difference frequency with TM mould generation cascade and the frequency of pump light new transition, produce new conversion ideler frequency light TM mould, the TE mould of the new conversion of ideler frequency light does not participate in cascade and frequently reacts, passes through PPLN ridge waveguide with difference frequency.Pump light remaining after conversion ideler frequency light TM and TE mould, reaction continues the second port that reverse transfer enters optical circulator, and conversion ideler frequency light TM and TE mould are exported by optical circulator the 3rd port.Pump light remaining after reaction is stopped, reflects by optoisolator when optical circulator the first port continues reverse transfer, can not return to the input end of pump light and flashlight, but by optical circulator the second port, again return to PPLN ridge waveguide again.
When with frequently react with difference frequency after remaining pump light with conversion ideler frequency light, from the 3rd port of optical circulator, export, by the first fiber grating and the second fiber grating, reflected, return to PPLN ridge waveguide and recycle.The magneto-optic memory technique of 90 ℃ of rotating mirrors of faraday can absorb approximate frequency doubled light with frequency light, play and the effect of lightwave filter frequently.If what produce in PPLN ridge waveguide during fl transmission has residue with frequency light, unfavorable to the cascade reaction of reverse transfer.
In transmission and course of reaction, be perfect condition, be in complete loss-free situation, the polarization direction of the linearly polarized light after conversion and vertical X-axis angulation θ=45 °, the pump light that is to say linear polarization in PPLN ridge waveguide, resolve into amplitude scale be 1 to 1 TM mould and TE mould.But due to the loss of PPLN ridge waveguide, the existence of the various losses such as coupling loss, θ will depart from 45 ° minutely.On the other hand, TM mould participates in reaction when fl transmission; And do not participate in reaction during TE mould fl transmission, but there is certain loss, to TE mould be reduced in the rear conversion efficiency that participates in reaction to when transmission, cause the conversion efficiency of final TE mould to be less than the conversion efficiency of TM mould, therefore while requiring to inject PPLN optical waveguide, the TE mould power of pump light is slightly larger, to make up the loss of TE mould.Therefore the value of θ should be greater than 45 °, the method for determining is as follows:.
According to pump light TE mould and TM mode amplitude than the graph of relation with the ideler frequency polarization degree ratio of total light intensity (polarized light intensity with).
TE mould and the TM mode amplitude of the first pump light are respectively A
p1and A (TE)
p1(TM),
TE mould and the TM mode amplitude of the second pump light are respectively A
p2and A (TE)
p2(TM),
After conversion, TE mould and the TM mode amplitude of unused light are respectively A
iand A (TE)
i(TM),
Require the TE mould of every bundle pump light to equate with the ratio of TM mode amplitude,
That is: tg θ=Ap1 (TE)/Ap1 (TM)=Ap2 (TE)/Ap2 (TM),
Meanwhile, the TE mould of ideler frequency light equates with TM mode amplitude,
That is: Ai (TE)=Ai (TM),
The analytic solution formula of ideler frequency light is:
By the analytic solution formula of above-mentioned condition substitution ideler frequency light, draw pump light TE mould and TM mode amplitude than the graph of relation with ideler frequency polarization degree (ratio of polarized light intensity and total light intensity).The ratio of corresponding TE and TM amplitude when obtaining ideler frequency polarization degree on this curve and be zero, the value of tg θ, tries to achieve angle θ.
The magnetic induction density B of faraday cell in this method fine adjustments linearly polarized light conversion equipment, be the polarization direction of the linear polarization pump light after the conversion of fine tune linearly polarized light conversion equipment and vertical X-axis angulation θ, making TM mould and TE mode amplitude ratio that linear polarization pump light decomposes in PPLN ridge waveguide is 1 to 1.
Compared with prior art, a kind of cascade of the present invention and frequency are with the advantage of difference frequency All Optical Wave Converter and conversion method: 1, the combination of PPLN ridge waveguide and faraday rotator mirror, solved well conversion ideler frequency light and signal polarisation of light relevant issues, flashlight polarization direction does not affect conversion ideler frequency light intensity; 2, by the magnetic induction density B of faraday cell in fine adjustments linearly polarized light conversion equipment, just can change the polarization direction of pump light, when using different PPLN ridge waveguides, having different various loss factors, as long as regulate the pump light output wavelength of two tunable external cavity lasers, regulate the magnetic induction density B of faraday cell, fine tune θ, can realize the wavelength conversion irrelevant with flashlight polarization state again, in wider wavelength coverage, improve wavelength conversion efficiency, favorable expandability; 3, the introducing of PPLN ridge waveguide, has improved the conversion efficiency of changing ideler frequency light; Reflectance spectrum centre wavelength is two fiber gratings of two pump light wavelength, can reflect the pump light that has neither part nor lot in and frequently react with difference frequency, makes it to return PPLN ridge waveguide recycling, has improved the utilization factor of pump light, has improved conversion efficiency; 4, the group delay that between flashlight and conversion ideler frequency light, polarization brings, in transmitting procedure by rotational automatic compensation of polarization of 90 ° of rotating mirrors of faraday, so there is not polarization dependent loss between the two.
Accompanying drawing explanation
Fig. 1 is this cascade and frequency and difference frequency All Optical Wave Converter example structure schematic diagram;
Fig. 2 is the structural representation of the PPLN ridge waveguide in Fig. 1;
Fig. 3 is the linearly polarized light conversion device structure schematic diagram in Fig. 1;
Fig. 4 be this cascade and frequently with the conversion method embodiment of difference frequency All Optical Wave Converter in the graph of relation of the TE mould that decomposes in waveguide of degree of polarization and linear polarization pump light and the ratio of TM amplitude;
Fig. 5 is this cascade and the conversion efficiency of conversion method embodiment and the graph of relation of signal light wavelength of frequency with difference frequency All Optical Wave Converter;
Fig. 6 is this cascade and the conversion efficiency of conversion method embodiment and the graph of relation of flashlight polarization angle of frequency with difference frequency All Optical Wave Converter;
Number in the figure is:
1, the first laser instrument, 2, second laser, the 3, first Polarization Controller, 4, the second Polarization Controller, 5, Polarization Controller, 6, linearly polarized light conversion equipment, 61, the first faraday cell, the 62, second faraday cell, the 7, first photo-coupler, 8, the second photo-coupler, 9, Erbium-Doped Fiber Amplifier (EDFA), 10, optoisolator, 11, optical circulator, 12, PPLN ridge waveguide, 13,90 ° of rotating mirrors of faraday, 14, the first fiber grating, the 15, second fiber grating.
Embodiment
Below in conjunction with embodiment and accompanying drawing, the present invention is further detailed explanation.
A kind of cascade and frequency and difference frequency All Optical Wave Converter embodiment
A kind of cascade and frequently with difference frequency All Optical Wave Converter embodiment as shown in Figure 1, comprise the first laser instrument 1, second laser 2, the first Polarization Controller 3, the second Polarization Controller 4, Polarization Controller 5, linearly polarized light conversion equipment 6, the first photo-coupler 7, the second photo-coupler 8, Erbium-Doped Fiber Amplifier (EDFA) 9, optoisolator 10, optical circulator 11, PPLN ridge waveguide 12,90 ° of rotating mirrors of faraday, 13, the first fiber gratings 14 and the second fiber grating 15.
The first laser instrument 1 and second laser 2 are tunable external cavity laser, the the first pump light wavelength sending is that 1530nm, the second pump light wavelength are 1570nm, access respectively the first Polarization Controller 3 and the second Polarization Controller 4, the output of the first Polarization Controller 3 and the second Polarization Controller 4 is respectively through polarization maintaining optical fibre tie-in line polarized light conversion device 6, linearly polarized light conversion equipment 6 changes the polarization direction of the pump light TM mould of directions X polarization, the polarization direction of the linear polarization pump light after conversion and the transverse cross-section parallel of PPLN ridge waveguide, and with the vertical angled θ of X-axis.Two bunch polarized pump light after conversion access the first photo-coupler 7 couplings, access the second photo-coupler 8 with together with flashlight through the random polarization state of Polarization Controller 5 again, the output access Erbium-Doped Fiber Amplifier (EDFA) 9 of the second photo-coupler 8, the output of Erbium-Doped Fiber Amplifier (EDFA) 9 is through the first port of optoisolator 10 access optical circulators 11, the light beam of the fl transmission of optical circulator 11 second port outputs is after PPLN ridge waveguide 12, light beam is by 13 reflections of 90 ° of rotating mirrors of faraday, the light beam of backward transmission enters again PPLN optical waveguide 12, the conversion ideler frequency light producing is output as the output of this wavelength shifter through the 3rd port of optical circulator 11.
This routine PPLN ridge waveguide 12 as shown in Figure 2, the substrate of this ridge waveguide is lithium niobate crystal chip, and ducting layer is that Z cuts the period polarized zinc niobate lithium wafer of mixing, and substrate and ducting layer pass through Direct Bonding, the square section of ridge waveguide is the XOY plane perpendicular to Z axis, is called Z tangent plane.PPLN ridge waveguide both can transmit TM mould, can transmit TE mould again.The waveguide length of this routine PPLN ridge waveguide 12 is 5cm.The polarization direction of the linear polarization pump light after these routine linearly polarized light conversion equipment 6 conversions as shown in Fig. 2 double-head arrow line segment, parallel with XOY plane and with the angled θ of vertical direction X-axis.
This routine linearly polarized light conversion equipment 6 as shown in Figure 3, comprises the first faraday cell 61 and the second faraday cell 62, and the relational expression in the angle θ that the linearly polarized light vibration plane by faraday cell turns over and the magnetic field of faraday cell is:
θ=VBL
In formula, B is the magnetic induction density in faraday cell, and L is the length of magnetic opticity material, and V is scale-up factor, Wei Erde constant.
First, second linear polarization pump light after conversion accesses respectively the first faraday cell 61 and the second faraday cell 62.
A kind of cascade and the conversion method embodiment of frequency with difference frequency All Optical Wave Converter
This example is used above-mentioned cascade and frequency and difference frequency All Optical Wave Converter embodiment, and conversion method is as follows:
First, second pump light that the first laser instrument 1 and second laser 2 send accesses respectively the first Polarization Controller 3 and the second Polarization Controller 4, adjusting first, second pump light polarization direction is TM mould, through polarization maintaining optical fibre tie-in line polarized light conversion device 6, linearly polarized light conversion equipment 6 the TM mould pump light of directions X polarization change into polarization direction and PPLN ridge waveguide transverse cross-section parallel and with the linearly polarized light of the angled θ of vertical direction X-axis.The linear polarization pump light of 2 kinds of wavelength after conversion after the first photo-coupler 7 with together with flashlight through the random polarization state of Polarization Controller 5 by the second photo-coupler 8 couplings, after amplifying through Erbium-Doped Fiber Amplifier (EDFA) 9 again, the first port by optical circulator 11 enters, and by the second port of optical circulator 11, exports, is coupled into for the first time simultaneously PPLN ridge waveguide 12.Linear polarization pump light in PPLN ridge waveguide 12 after conversion is decomposed into TE mould and TM mould, and the amplitude ratio of TE mould and TM mould equals tg θ.PPLN ridge waveguide 12 transmits TM mould and TE mould simultaneously, and the now TM mould generation cascade of the TM mould of flashlight and pump light and frequency react, produce conversion ideler frequency light TM mould with difference frequency, and the TE mould of flashlight does not participate in cascade and frequently reacts with difference frequency in fl transmission process.The ideler frequency light TM mould that PPLN ridge waveguide 12 produces, flashlight TE mould and pump light TE mould continue transmission forward, arriving 90 ° of rotating mirrors 13 of faraday is reflected, return and carry out backward transmission, now, the ideler frequency light TM mould that the reflection of 90 ° of rotating mirrors 13 of faraday produces while making fl transmission changes TE mould into, flashlight TE mould changes TM mould into, the TE mould of linear polarization pump light changes TM mould into, backward transmission enters PPLN ridge waveguide 12, the TM mould of flashlight new transition reacts with difference frequency with TM mould generation cascade and the frequency of pump light new transition, produce new conversion ideler frequency light TM mould, the TE mould of the new conversion of ideler frequency light does not participate in cascade and frequently reacts with difference frequency, by PPLN ridge waveguide 12.Pump light remaining after conversion ideler frequency light TM and TE mould, reaction continues the second port that reverse transfer enters optical circulator 11, and conversion ideler frequency light TM and TE mould are exported by optical circulator 11 the 3rd port.Pump light remaining after reaction is stopped, reflects by optoisolator 10 when optical circulator 11 first ports continue reverse transfer, can not return to the input end of pump light and flashlight, but by optical circulator 11 second ports, again return to PPLN ridge waveguide 12 again.When with frequently react with difference frequency after remaining pump light with conversion ideler frequency light, from the 3rd port of optical circulator 11, export, by the first fiber grating 14 and the second fiber grating 15 reflections, back light circulator 11, enter PPLN ridge waveguide 12 again and recycle.
The magnetic induction density B of first, second faraday cell 61,62 in fine adjustments linearly polarized light conversion equipment 6, get final product the polarization direction of the linear polarization pump light after 6 conversions of fine tune linearly polarized light conversion equipment and vertical X-axis angulation θ, making TM mould and TE mode amplitude ratio that linear polarization pump light decomposes in PPLN ridge waveguide 12 is 1 to 1.
Figure 4 shows that the relation curve of TE mode amplitude Ap (TE) that in the present embodiment, degree of polarization and linear polarization pump light decompose in waveguide and the ratio of TM mode amplitude Ap (TM), in figure, curve is known, when degree of polarization is 0dB, the amplitude ratio Ap of TE mould and TM (TE)/Ap (TM) is 1.096, be tg θ=1.096, by trigonometric function, obtain this routine θ value.
Each analog parameter of the present embodiment is: first, second pump light wavelength is respectively 1530nm and 1570nm, and optical wavelength is 774.871nm frequently, flashlight centre wavelength 1545nm, conversion ideler frequency optical wavelength 1554.5nm.Polarization cycle is 16.754um, and the waveguide loss of 1550nm wavelength is 0.2dB/cm, and the waveguide loss of 775nm is 0.4dB/cm, and the waveguide length of PPLN ridge waveguide is 5cm.
Shown in Fig. 5, be the conversion efficiency of this conversion method embodiment and the graph of relation of signal light wavelength; In figure, block curve is the conversion efficiency of TE mould flashlight, and dashed curve is the conversion efficiency of TM mould flashlight.When the polarization direction of first, second pump light and the transverse cross-section parallel of PPLN ridge waveguide 12 and while becoming above-mentioned angle θ (tg θ=1.096) with vertical direction X-axis, signal light wavelength is in 1520nm to 1580nm scope, the flashlight tuning curve of this routine TE mould and TM mould almost overlaps, polarization correlated very little.
Shown in Fig. 6, be the conversion efficiency of this conversion method embodiment and the graph of relation of flashlight polarization angle, in figure, block curve is the conversion efficiency of TE mould flashlight, dashed curve is the conversion efficiency of TM mould flashlight, article two, curve is all horizontal line substantially, and the polarization angle of the flashlight of this routine TE mould and TM mould and conversion efficiency are irrelevant as seen.
Above-described embodiment, is only the specific case that object of the present invention, technical scheme and beneficial effect are further described, and the present invention is not defined in this.All any modifications of making, be equal to replacement, improvement etc., within being all included in protection scope of the present invention within scope of disclosure of the present invention.
Claims (7)
1. cascade and frequency and a difference frequency All Optical Wave Converter, comprise laser instrument, Polarization Controller, photo-coupler, Erbium-Doped Fiber Amplifier (EDFA), optoisolator, optical circulator, PPLN optical waveguide, 90 ° of rotating mirrors of faraday, it is characterized in that:
The first laser instrument (1) and second laser (2) are tunable external cavity laser, the first pump light sending and the second pump light access respectively the first Polarization Controller (3) and the second Polarization Controller (4), the output of the first Polarization Controller (3) and the second Polarization Controller (4) accesses after the first photo-coupler (7) coupling, access the second photo-coupler (8) with together with the flashlight of random polarization state through Polarization Controller (5), the output access Erbium-Doped Fiber Amplifier (EDFA) (9) of the second photo-coupler (8), the output of Erbium-Doped Fiber Amplifier (EDFA) (9) is through optoisolator (10) access optical circulator (11) first ports, the light beam of the fl transmission of optical circulator (11) second port outputs is after PPLN optical waveguide (12), light beam is reflected by 90 ° of rotating mirrors of faraday (13), the light beam of backward transmission enters again PPLN optical waveguide (12), the conversion ideler frequency light producing is output as the output of this wavelength shifter from the 3rd port of optical circulator (11),
Described the first pump light, the second pump light and flashlight are C-band.
2. cascade according to claim 1 and frequency and difference frequency All Optical Wave Converter, is characterized in that:
Described PPLN optical waveguide (12) is PPLN ridge waveguide, and the substrate of this PPLN ridge waveguide is lithium niobate crystal chip, and ducting layer is that Z cuts the period polarized zinc niobate lithium wafer of mixing, substrate and ducting layer Direct Bonding, and the square section of ridge waveguide is the XOY plane perpendicular to Z axis;
Respectively through first, second pump light tie-in line polarized light conversion device (6) of the first Polarization Controller (3) and the second Polarization Controller (4), then access the first photo-coupler (7); Linearly polarized light conversion equipment (8) is converted to the pump light of the TM pattern of directions X polarization the transverse cross-section parallel of polarization direction and PPLN ridge waveguide, and with the linearly polarized light of the vertical angled θ of X-axis.
3. cascade according to claim 2 and frequency and difference frequency All Optical Wave Converter, is characterized in that:
Described linearly polarized light conversion equipment (6) comprises the first faraday cell (61) and the second faraday cell (62), and the relational expression in the angle θ that the linearly polarized light vibration plane by faraday cell turns over and the magnetic field of faraday cell is:
θ=VBL
In formula, B is the magnetic induction density in faraday cell, and L is the length of magnetic opticity material, and V is scale-up factor Wei Erde constant,
Described first, second pump light enters respectively the first faraday cell (61) and second faraday cell (62) of linearly polarized light conversion equipment.
4. cascade according to claim 3 and frequency and difference frequency All Optical Wave Converter, is characterized in that:
Each accesses the first photo-coupler (7) through polarization maintaining optical fibre the output of described the first Polarization Controller (3) and the second Polarization Controller (4).
5. cascade according to claim 4 and frequency and difference frequency All Optical Wave Converter, is characterized in that:
On the optical fiber that described optical circulator (11) the 3rd port connects, be connected to the first fiber grating (14) and the second fiber grating (15), the reflectance spectrum centre wavelength of the first fiber grating (14) and the second fiber grating (15) is respectively the first pump light and the second pumping light wavelength.
6. cascade according to claim 5 and the conversion method of frequency with difference frequency All Optical Wave Converter, is characterized in that:
The first pump light that the first tunable laser (1) and the second tunable laser (2) are sent and the second pump light access respectively the first Polarization Controller (3) and the second Polarization Controller (4), adjust its polarization direction, making the first pump light and the second pump light is TM mould, the output of the first Polarization Controller (3) and the second Polarization Controller (4) is respectively through polarization maintaining optical fibre tie-in line polarized light conversion device (6), linearly polarized light conversion equipment (6) changes the TM mould pump light of directions X polarization into the transverse cross-section parallel of polarization direction and PPLN ridge waveguide (12), and with the linearly polarized light of the angled θ of vertical direction X-axis, the linear polarization pump light of 2 kinds of wavelength after conversion after the first photo-coupler (7) with together with the flashlight of random polarization state through Polarization Controller (5) by the second photo-coupler (8) coupling, after passing through again Erbium-Doped Fiber Amplifier (EDFA) (9) amplification, the first port by optical circulator (11) enters, from the second port of optical circulator (11), export, be coupled into for the first time simultaneously PPLN ridge waveguide (12), linear polarization pump light in PPLN ridge waveguide (12) after conversion is decomposed into TE mould and TM mould, and the amplitude ratio of TE mould and TM mould equals tg θ, PPLN ridge waveguide (12) transmits TM mould and TE mould simultaneously, the now TM mould generation cascade of the TM mould of flashlight and pump light and frequency react, produce conversion ideler frequency light TM mould with difference frequency, the TE mould of flashlight does not participate in cascade and frequently reacts with difference frequency in fl transmission process, the ideler frequency light TM mould that PPLN ridge waveguide (12) produces, flashlight TE mould and pump light TE mould continue transmission forward, arrive 90 ° of rotating mirrors of faraday (13), the ideler frequency light TM mould producing when the rotary reflection of 90 ° of rotating mirrors of faraday (13) makes fl transmission changes the TE mould that TE mould, flashlight TE mould change TM mould, linear polarization pump light into into and changes TM mould into, and transfer backward transmission to and enter PPLN ridge waveguide (12), the TM mould of flashlight new transition reacts with difference frequency with TM mould generation cascade and the frequency of pump light new transition, produce new conversion ideler frequency light TM mould, the TE mould of the new conversion of ideler frequency light does not participate in cascade and frequently reacts, passes through PPLN ridge waveguide (12) with difference frequency, pump light continuation reverse transfer remaining after conversion ideler frequency light TM and TE mould, reaction enters optical circulator (11) second ports, conversion ideler frequency light TM and TE mould are by optical circulator (11) the 3rd port output, pump light remaining after reaction is stopped, reflects by optoisolator (10) when optical circulator (11) first ports continue reverse transfer, again returns to PPLN ridge waveguide (12) again by optical circulator (11) second ports, pump light remaining after reacting with difference frequency with frequency is exported from the 3rd port of optical circulator (11) with conversion ideler frequency light, by the first fiber grating (14) and the second fiber grating (15), is reflected, returns PPLN ridge waveguide (12) recycling.
7. cascade according to claim 6 and the conversion method of frequency with difference frequency All Optical Wave Converter, is characterized in that:
The magnetic induction density B of 2 faraday cells in fine adjustments linearly polarized light conversion equipment (6), be the polarization direction of the linear polarization pump light after fine tune linearly polarized light conversion equipment (6) conversion and vertical X-axis angulation θ, making TM mould and TE mode amplitude ratio that linear polarization pump light decomposes in PPLN ridge waveguide (12) is 1 to 1.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114362829B (en) * | 2021-12-21 | 2024-05-03 | 济南量子技术研究院 | PPLN-based polarization independent frequency conversion method, device and single photon detector |
| CN116184567A (en) * | 2023-03-09 | 2023-05-30 | 武汉安湃光电有限公司 | Broadband optical frequency doubling waveguide chip with high temperature tuning efficiency |
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