CN103744249A - Device and method for generating broadband OFC (Optical Frequency Comb) - Google Patents

Abstract

The invention discloses a method for generating a broadband OFC (Optical Frequency Comb). A 50 line broadband optical frequency comb is generated by adopting a cascade structure of a DPMZM (Double-Parallel Mach-Zehnder Modulator) and two Mach-Zehnder IMs (Intensity Modulators) and adjusting a radio frequency amplitude and a direct current offset voltage of each modulator, the power is smooth, and the interval between spectral lines is adjustable. The optical comb performance generated in the scheme is relatively good, and great significance is achieved for the application and development of the broadband OFC in the optical communication field. The system structure of the device and method for generating the broadband OFC is relatively simple, easy to implement, and conductive to reducing the system cost.

Description

A kind of generation device of Reflection Optical Thin Film frequency comb and method thereof

Technical field

The present invention relates to optical communication technique field, be specifically related to a kind of external modulation technology of utilizing laser and produce frequency band broadness, variable spaced, power is smooth and rejection ratio is high optical frequency com generating apparatus and method thereof.

Background technology

Optical frequency com (Optical Frequency Comb, OFC) refers to the spectrum that frequency component even by a series of intervals and phase coherence forms on frequency spectrum, and main performance index has light comb line number, spectral line interval and flatness etc.Along with the continuous growth of communication requirement and the develop rapidly of the communication technology, optical wavelength-division multiplex (WDM) and light OFDM (OFDM) technology become study hotspot gradually, and limit the light carrier that one of bottleneck of these System Developments is a large amount of wavelength differences of needs, power is smooth.The use of optical frequency com can address this problem, and greatly reduces system cost, and the application and development of optical communication technique is had very important significance.

In addition, optical frequency com also has a wide range of applications at aspects such as the generation of optics random waveform and multi-wavelength ultrashort pulse generations.Wherein, aspect any waveform generation, spectral line number, spectral line interval, flatness and the rejection ratio of optical frequency com is crucial several parameters.For the application of these optical communication fields, we need to produce frequency band broadness, variable spaced, power is smooth and rejection ratio is high optical frequency com, and simultaneity factor structure should be tried one's best simply.

According to pertinent literature, the production method of Reflection Optical Thin Film frequency comb mainly contains: optical non-linear effect, light feedback loop, micro-resonant cavity and electrooptic modulator method etc.Wherein, nonlinear effect method mainly adopts optics four wave mixing technology, and the optical frequency com line number of generation is a lot of but power swing is larger, and its application has limitation; Utilize the system of light feedback loop spread-spectrum, generally comparatively complicated wayward; And the work period of design micro-resonant cavity is long and cost is higher.Based on electrooptic modulator, produce the method for Reflection Optical Thin Film frequency comb, system architecture is simple, spectral line variable spaced and flatness better, be the very promising optical frequency com generation of one technology.But the light comb line number that electrooptic modulator method produces is at present also relatively limited, needs to continue to be studied and propose to produce wide band method.

Summary of the invention

In view of the deficiencies in the prior art, simultaneously in order to meet the practical application of optical communication, need to produce a kind of Reflection Optical Thin Film frequency comb of better performances.The present invention adopts the scheme of two parallel MZ Mach-Zehnders (DPMZM) and mach zhender intensity modulator (IM) cascade, by regulating radio frequency amplitude and the DC offset voltage of cascaded modulator, produced 50 live width band optical frequency coms, and power is super smooth.Light comb line number that this scheme produces is more and spectral line interval is adjustable, and the application and development to it at optical communication field is significant.

Specifically, the present invention is by cascade DPMZM and two IM, by different radio frequency amplitude and DC offset voltage are set, realize DPMZM output power equate ± 2 rank optical sidebands, and two IM duties are identical, can produce respectively the smooth light comb of 5 line, 0 rank, ± 1 rank and ± 2 rank optical sideband power that IM produces equate.The optical sideband that after in this scheme, one-level modulator produces previous stage modulator is used as respectively light source and is modulated, thereby constantly increases light comb line number, finally produces 50 line flat optical frequency coms, has realized the expansion of frequency spectrum.

To achieve these goals, the technical solution used in the present invention is as follows:

A production method for Reflection Optical Thin Film frequency comb, said method comprising the steps of:

Step 1, it is λ that described laser instrument sends wavelength, angular frequency is ω _c, amplitude is E _inlight wave be input in two parallel MZ Mach-Zehnders; Wherein, inject the polarization direction of light wave through described Polarization Controller adjustment, make it consistent with the polarization direction of two parallel MZ Mach-Zehnders;

Step 2, take frequency as f ₁, angular frequency is ω ₁, amplitude is V _rF1the sub-modulator MZ-a of upper arm of the two parallel MZ Mach-Zehnders of radio frequency signals drive, the DC offset voltage of its work is V _dC1=0, be operated in maximum point, the carrier wave producing and ± 2 rank sidebands are respectively:

E ₀(t)=E _inexp(jω _ct)J ₀(m ₁)，

E _±2(t)=E _inexp[j(ω _ct±2ω ₁t)]J ₂(m ₁)；

Step 3, the not modulated radio signal of the sub-modulator MZ-b of underarm of two parallel MZ Mach-Zehnders, only arranges its DC voltage V _dC2; And MAIN MUX MZ-c DC voltage is set is V _dC3=V _π, go up the sub-modulator output signal of underarm and produce 180 ° of phase shifts; Wherein, the optical carrier of sub-modulator MZ-b output is:

$E_{\mathrm{MZ}-b}\left(t\right)=\frac{E_{\mathrm{in}}}{2}\mathrm{expj}\left({\mathrm{\ω}}_{c}t\right)[\exp \left(j{\mathrm{\φ}}_{\mathrm{DC}2}\right)+\exp (-j{\mathrm{\φ}}_{\mathrm{DC}2})];$

Step 4, regulates DC voltage V _dC2, make the light carrier constant amplitude of the sub-modulator output of underarm anti-phase, thereby cancel out each other, now cos φ _dC2=J ₀(m ₁), meet the parameter m of this expression formula ₁=π V _rF1/ V _πand φ _dC2=π V _dC2/ V _πhave or not array value, as m ₁=1.66, φ _dC2=1.14 or m ₁=1.44, φ _dC2=0.996 etc.; Ignore high-order term, final described two only export ± 2 rank optical sidebands of parallel MZ Mach-Zehnder, sideband is spaced apart 4f ₁;

Step 5, take frequency as f ₂=0.8f ₁, angular frequency is ω ₂=0.8 ω ₁, amplitude is V _rF2radio frequency signals drive the first light intensity modulator, the DC voltage of its work is V _dC4, and suppose that described two parallel MZ Mach-Zehnder output optical signal is E _dPMZ(t), the first light intensity modulator is output as:

$E_{\mathrm{IM}1}\left(t\right)=\frac{E_{\mathrm{DPMZ}}\left(t\right)}{2}\underset{n=-\&infin;}{\overset{+\&infin;}{\mathrm{\&Sigma;}}}[J_n\left(m_2\right)e^{\mathrm{jn}{w}_{2}t+j{\mathrm{\&phi;}}_{\mathrm{<figure-callout\; id="4"\; label="DC"\; filenames="HDA0000449448970000011.png"\; state="\{\{state\}\}">DC</figure-callout>}4}}+J_n(-m_2)e^{\mathrm{jn}{w}_{2}t-j{\mathrm{\&phi;}}_{\mathrm{DC}4}}],$

The carrier wave, ± 1 rank and ± 2 rank optical sidebands that now produce are respectively:

$E_0\left(t\right)=\frac{E_{\mathrm{DPMZ}}\left(t\right)}{2}{J}_0\left(m_2\right)[\exp \left({\mathrm{j\&phi;}}_{\mathrm{DC}4}\right)+\exp (-j{\mathrm{\&phi;}}_{\mathrm{DC}4})],$

$E_{\&PlusMinus;1}\left(t\right)=\&PlusMinus;\frac{E_{\mathrm{DPMZ}}\left(t\right)}{2}\exp (\&PlusMinus;{\mathrm{j\&omega;}}_{0}t)J_1\left(m_2\right)[\exp \left({\mathrm{j\&phi;}}_{\mathrm{DC}4}\right)-\exp (-j{\mathrm{\&phi;}}_{\mathrm{DC}4})],$

$E_{\&PlusMinus;2}\left(t\right)=\frac{E_{\mathrm{DPMZ}}\left(t\right)}{2}\exp (\&PlusMinus;\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA0000449448970000011.png"\; state="\{\{state\}\}">j</figure-callout>}2{\mathrm{\&omega;}}_{0}t)J_2\left(m_1\right)[\exp \left(j{\mathrm{\&phi;}}_{\mathrm{DC}4}\right)+\exp (-j{\mathrm{\&phi;}}_{\mathrm{DC}4})];$

By radiofrequency signal amplitude V is set _rF2with DC voltage V _dC4, make:

|E ₀(t)|=|E _±1(t)|=|E _±2(t)|，

Now modulation index is m ₂=π V _rF2/ V _π=1.84, the phase that direct current causes _dC4=π V _dC4/ V _π≈ 0.5, has produced the smooth light comb of 5 line, and has been 2 lines of described two parallel MZ Mach-Zehnder outputs to be used as respectively to light source modulate, thereby has produced the smooth light comb of 10 line;

Step 6, driving the radio frequency signal frequency of the second light intensity modulator is f ₃=0.16f ₁, according to step 5 to radio frequency amplitude V _rF3with DC voltage V _dC5carry out identical setting, also can produce the smooth light comb of 5 line, and be 10 lines of the first light intensity modulator output to be used as respectively to light source modulate, thereby produced the smooth light comb of 50 line;

Further, the device of realizing Reflection Optical Thin Film frequency comb production method of the present invention comprises by two parallel MZ Mach-Zehnders and two cascade structures that mach zhender intensity modulator forms.

It should be noted that, described two parallel MZ Mach-Zehnders are Dual Drive port.

It should be noted that, described cascade structure can produce 50 live width band flat optical frequency coms, and spectral line interval is adjustable.

As application, Reflection Optical Thin Film frequency comb generation device of the present invention, is applicable in WDM and ofdm system as multi wave length illuminating source, or is used for producing random waveform and ultrashort light pulse.

What need to further illustrate is, the present invention is the structure based on three Mach-Zehnder modulators cascades, by setting the amplitude of each modulator radio-frequency signal source and the size of direct voltage source, obtain needed optical frequency com, there is broad spectral bandwidth and smooth spectral line power.In addition, this scheme is simple in structure, is conducive to reduce system cost.

Beneficial effect of the present invention is, by radio frequency amplitude and the DC voltage of cascading Mach-Zehnder modulators are set, has produced Reflection Optical Thin Film frequency comb, spectral line there is super smooth luminous power and interval adjustable.Present device is simple, can greatly reduce the quantity of light source in wdm system and ofdm system, thereby reduces system cost, and is applicable to very much for producing random waveform and ultrashort light pulse, and contrast prior art has larger advantage.

Accompanying drawing explanation

Fig. 1 is structural representation of the present invention;

Fig. 2 is respectively DPMZM in the present invention and produces 2 lines, and an IM produces 10 lines, finally produces the output spectrum figure of 50 lines.

Embodiment

Below in conjunction with accompanying drawing, embodiments of the invention are elaborated.It should be noted that, the present embodiment is implemented under take technical solution of the present invention as prerequisite, provided detailed embodiment and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

As shown in Figure 1, the present invention is a kind of generation device of Reflection Optical Thin Film frequency comb, and described device comprises laser instrument 1, Polarization Controller 2, Polarization Controller 8, Polarization Controller 12, radio-frequency signal source 4, radio-frequency signal source 10, radio-frequency signal source 14, direct voltage source 5, direct voltage source 6, direct voltage source 7, direct voltage source 11, direct voltage source 15, two parallel Mach-increasing Dare modulator 3, Mach-increasing Dare intensity modulator 9, Mach-increasing Dare intensity modulator 13 and spectroanalysis instrument (OSA) 16.The light source output port of described laser instrument 1 joins with the input port of two parallel Mach-increasing Dare modulators 3, the rf inputs mouth of the output port of first radio-frequency signal source 4 and DPMZM modulation MZ-a joins, and direct voltage source 5, direct voltage source 6, direct voltage source 7 output ports are connected with three direct current mouth a, b, the c of two parallel Mach-increasing Dare modulators 3 respectively; The output port of two parallel Mach-increasing Dare modulators 3 joins with the input port of Mach-increasing Dare intensity modulator 9, the rf inputs mouth of the output port of radio-frequency signal source 10 and Mach-increase Dare intensity modulator 9 joins, and the output terminal of direct voltage source 11 joins with the DC port of the Mach-increasing Dare intensity modulator 9; The input port of Mach-increasing Dare intensity modulator 13 joins with the output port of Mach-increasing Dare intensity modulator 9, and radio-frequency signal source 14 and direct voltage source 15 join with rf inputs mouth and the DC port of Mach-increasing Dare intensity modulator 13 respectively; Output port and the spectroanalysis instrument (OSA) 16 of Mach-increasing Dare intensity modulator 13 join, and measure the spectrogram of this device generation Reflection Optical Thin Film frequency comb.

In this example, use the method for described device generation Reflection Optical Thin Film frequency comb as follows:

Step 1, light source produces the continuous light wave that operation wavelength is 1550nm, it is two parallel Mach-increasing Dare modulator that 5V, extinction ratio are 30dB that continuous light wave is input to half-wave voltage, the suitable signal of first radio-frequency signal source output 25GHz amplitude, arranges respectively first and the voltage of the 3rd direct voltage source output 0V and 5V.Regulate the size of second direct voltage source, thereby offset 0 rank light carrier, finally two parallel Mach-increase Dare modulator output ± 2 rank optical sidebands, the smooth light of 2 line is combed.

Step 2, half-wave voltage is first Mach-Zehnder intensity modulator that 5V, extinction ratio are 30dB, the frequency of its radio-frequency (RF) driving signal is that 20GHz, amplitude are 2.93V, and its direct voltage output 0.80V is set, thereby produced the smooth light comb of 5 line, and be that 2 lines of two parallel Mach-increasing Dare modulator output are used as respectively to modulation of source, final first Mach-Zehnder intensity modulator is exported the smooth light comb of 10 line.

Step 3, second Mach-Zehnder intensity modulator of same model, the frequency that its radio-frequency (RF) driving signal is set is that 4GHz, amplitude are 2.93V, DC voltage is 0.80V, thereby also produce the smooth light comb of 5 line, and be first Mach-Zehnder intensity modulator to be exported to the smooth light comb of 10 line be used as respectively modulation of source, final second Mach-Zehnder intensity modulator exported the smooth light comb of 50 line, power flatness is in 1dB, and optical sideband rejection ratio is 13dB.

As shown in Figure 2, Fig. 2 a arranges two parallel Mach-increasing Dare modulator output ± 2 rank optical sidebands, i.e. the smooth light comb of 2 line, and Fig. 2 b is that the first Mach-Zehnder intensity modulator is exported the smooth light comb of 10 line; Fig. 2 c arranges the second Mach-Zehnder intensity modulator to export the smooth light comb of 50 line.

Further, analyze the performance of the Reflection Optical Thin Film frequency comb producing in the present invention, mainly comprise spectral bandwidth, spectral line number, power flatness and rejection ratio etc.Also have now radio frequency amplitude and the DC offset voltage value of each modulator.Specifically, the radiofrequency signal RF1 frequency that the sub-modulator MZ-a of two parallel Mach-increasing Dare modulator is set is 25GHz, amplitude is 2.3V, DC offset voltage DC1 is 0V, not modulated radio signal of sub-modulator MZ-b, DC offset voltage DC2 is 1.586V, the DC offset voltage of MAIN MUX is 5V, thereby produce 180 ° of phase shifts, the 2 linear lights combs that generation flatness is 0.01dB, rejection ratio is 18dB, because the extinction ratio of two parallel Mach-Zehnder modulators is set to current device actual value 30dB, so odd rank optical sideband does not disappear completely, along with the further raising of device level, 2 more pure linear light combs will be produced, the people such as Tetsuya Kawanishi in 2006 have proposed the two parallel Mach-Zehnder modulators of 70dB extinction ratio in U.S.'s optical-fibre communications symposial (OFC), the radiofrequency signal RF2 frequency of the first light intensity modulator is that 20GHz, amplitude are 2.93V, and DC offset voltage DC4 is 0.80V, the 10 linear lights combs that generation flatness is 0.2dB, and rejection ratio is 15dB, the radiofrequency signal RF3 frequency that the second light intensity modulator is set is that 4GHz, amplitude are 2.93V, and DC offset voltage DC5 is 0.80V, the 50 linear lights combs that generation flatness is 1dB, and spectral bandwidth is 196GHz, rejection ratio is 13dB.

For a person skilled in the art, can be according to technical scheme described above and design, make other various corresponding changes and distortion, and these all changes and distortion all should belong to the protection domain of the claims in the present invention within.

Claims (5)

1. a production method for Reflection Optical Thin Film frequency comb, is characterized in that, said method comprising the steps of:

Step 1, it is λ that described laser instrument sends wavelength, angular frequency is ω _c, amplitude is E _inlight wave be input in two parallel MZ Mach-Zehnders; Wherein, inject the polarization direction of light wave through described Polarization Controller adjustment, make it consistent with the polarization direction of two parallel MZ Mach-Zehnders;

Step 2, take frequency as f ₁, angular frequency is ω ₁, amplitude is V _rF1the sub-modulator MZ-a of upper arm of the two parallel MZ Mach-Zehnders of radio frequency signals drive, the DC offset voltage of its work is V _dC1=0, be operated in maximum point, the carrier wave producing and ± 2 rank sidebands are respectively:

E ₀(t)=E _inexp(jω _ct)J ₀(m ₁)，

E _±2(t)=E _inexp[j(ω _ct±2ω ₁t)]J ₂(m ₁)；

Step 3, the not modulated radio signal of the sub-modulator MZ-b of underarm of two parallel MZ Mach-Zehnders, only arranges its DC voltage V _dC2; And MAIN MUX MZ-c DC voltage is set is V _dC3=V _π, go up the sub-modulator output signal of underarm and produce 180 ° of phase shifts; Wherein, the optical carrier of sub-modulator MZ-b output is:

Step 4, regulates DC voltage V _dC2, make the light carrier constant amplitude of the sub-modulator output of underarm anti-phase, thereby cancel out each other, now cos φ _dC2=J ₀(m ₁), meet the parameter m of this expression formula ₁=π V _rF1/ V _πand φ _dC2=π V _dC2/ V _πhave or not array value, as m ₁=1.66, φ _dC2=1.14 or m ₁=1.44, φ _dC2=0.996 etc.; Ignore high-order term, final described two only export ± 2 rank optical sidebands of parallel MZ Mach-Zehnder, sideband is spaced apart 4f ₁;

Step 5, take frequency as f ₂=0.8f ₁, angular frequency is ω ₂=0.8 ω ₁, amplitude is V _rF2radio frequency signals drive the first light intensity modulator, the DC voltage of its work is V _dC4, and suppose that described two parallel MZ Mach-Zehnder output optical signal is E _dPMZ(t), the first light intensity modulator is output as:

The carrier wave, ± 1 rank and ± 2 rank optical sidebands that now produce are respectively:

By radiofrequency signal amplitude V is set _rF2with DC voltage V _dC4, make:

|E ₀(t)|=|E _±1(t)|=|E _±2(t)|，

Now modulation index is m ₂=π V _rF2/ V _π=1.84, the phase that direct current causes _dC4=π V _dC4/ V _π≈ 0.5, has produced the smooth light comb of 5 line, and has been 2 lines of described two parallel MZ Mach-Zehnder outputs to be used as respectively to light source modulate, thereby has produced the smooth light comb of 10 line;

Step 6, driving the radio frequency signal frequency of the second light intensity modulator is f ₃=0.16f ₁, according to step 5 to radio frequency amplitude V _rF3with DC voltage V _dC5carry out identical setting, also can produce the smooth light comb of 5 line, and be 10 lines of the first light intensity modulator output to be used as respectively to light source modulate, thereby produced the smooth light comb of 50 line.

2. a device that produces Reflection Optical Thin Film frequency comb claimed in claim 1, is characterized in that, described device comprises by two parallel MZ Mach-Zehnders and two cascade structures that mach zhender intensity modulator forms.

3. device according to claim 2, is characterized in that, described two parallel MZ Mach-Zehnders are Dual Drive port.

4. device according to claim 2, is characterized in that, described cascade structure can produce 50 live width band flat optical frequency coms, and spectral line interval is adjustable.

5. utilize the Reflection Optical Thin Film frequency comb generation device described in claim 2, can be used in WDM and ofdm system as multi wave length illuminating source, or be used for producing random waveform and ultrashort light pulse.

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