CN101013795A - Analog external cavity laser - Google Patents

Abstract

The present invention relates to the analog external cavity lasers (ECLs) including designs, materials, methods of manufacturing and methods of use for such ECLs and packages for such ECLS. Numerous criteria are presented that lead to improved cost/performance for ECLs and for systems incorporating such ECLs.

Description

Analog external cavity laser

The related application cross reference

The application's case according among 35 U.S.C. § 119, § 120, the § 365 one or more advocate on April 2nd, 2004 file an application the 60/558th, No. 927 temporary patent application cases, and filed an application on April 16th, 2004 the 60/562nd, the priority of the 60/638th, No. 679 temporary patent application case that No. 762 temporary patent application cases and on December 23rd, 2004 file an application.For various purposes, the full content of all described temporary patent application cases all is incorporated herein with way of reference.

Technical field

The present invention relates to the LASER Light Source field by and large, and more specifically, relates to the external cavity laser light source.

Background technology

Directly modulation profile formula feedback (DFB) laser diode is widely used in many application, comprises digital synchronous broadcasting and Narrowcasting (QAM form) in the multichannel transmission, cable TV (CATV) of the modulated-analog signal that is generally used for analog broadcasting and is used for the communication network of the distribution of video, data and IP-based speech transmissions.The DFB laser diode (perhaps, for making language abbreviate " DFB " for simplicity as) other application comprise by Optical Fiber Transmission radio frequency (RF) signal, wherein adopt the standard single-mode fiber (SMF) of widespread deployment by single strand optical fiber transmission RF signal with the wavelength of about 1310nm (1310 nanometer) usually.These are used only as illustration but not as limiting, because also there are and continuing other application of exploitation DFB laser diode.

For transmission is used for CATV and based on the RF of optical fiber, especially partly, under 1310nm wavelength situation, obtained desired systematic function substantially because use can produce and keep laser and other assemblies of acceptable low degree analog distortion.This kind analog distortion represented by various numerical parameters usually, for example compound second-order distortion (CSO or second order intermodulation distortion-IMD2 or second intermodulation product-IP2) and CTB distortion (CTB or IMD3 or IP3).By the combination of extremely low (being actually zero) chromatic dispersion under the 1310nm situation among low distortion Distributed Feedback Laser and the used SMF, can obtain and keep the analog distortion of desired low degree usually.Yet, by with CATV system, video and data transmission system, and be built into the wavelength that uses about 1550nm based on the RF transmission system of optical fiber and bring operation, will realize big potential advantage.These potential advantages partly stem from optics and amplify member (erbium-doped fiber amplifier for example, availability EDFA) and can utilize Wave division multiplexing (WDM) technology.Yet existing several factors has hindered CATV and distribution of wireless widespread deployment 1550nm network, and these factors comprise warble (Chirp) that is produced by direct modulation D FB laser.Warble can be unfriendly with the 1550nm wavestrip about standard SMF in non-zero dispersion and the gain slope among the typical EDFA interact, thereby serious restriction system performance, for example, as by people such as E.Bergmann at " the compound second-order distortion that causes by chromatic dispersion under the 1.5 μ m situations (Dispersion-induced Composite Second-Order Distortion at 1.5 μ m) " (IEEE PhotonicsTech.Lett., the 3rd volume, No. 1,59-61 page or leaf (in January, 1991)) described in.

In addition, owing to satisfy the more requirement of high-performance, low-cost reflector so far as yet, the deployment of new more effective modulation scheme is delayed.For example, Quadrature Phase Shift Keying (QPSK) modulation technique can make the bit transfer rate of system double and the required bandwidth of electric assembly in can the increase system potentially.In addition, the QPSK modulation technique can provide under identical system bits rate behavior potentially than the more compact frequency spectrum of the available frequency spectrum of binary modulated.Yet, utilize the QPSK technology need use low-cost lasing light emitter that line width is narrower than current commercially available typical DFB (for example usually, referring to " the 8Gb/s QPSK optical homodyne test experience (An 8Gb/s QPSK optical Homodyne Detection Experiment Using External-Cavity LaserDiodes) of using external cavity laser diode to carry out " that the people showed such as S.Norimatsu, IEEE Photonics Tech.Lett., the 4th volume, No. 7, the 765-767 page or leaf, in July, 1992).

Hindering one of them major obstacle that is extensive use of direct modulation D FB about 1550nm is high the warbling and high relatively inherent distortion of independent Distributed Feedback Laser.These effects occurring mainly is because of three kinds of physical phenomenons (i) effects of spatial, (ii) leakage current, and (iii) inherent nonlinearity response.

Limiting near another limiting factor that direct modulation D FB moves 1550nm is the big relatively line width of the 1MHz order of magnitude.The relative intensity noise (RIN) of this line width meeting limit laser device, and relative intensity noise (RIN) can limit the transmission carrier-to-noise than (CNR).These effects can cause in the high channel load and more the transmission performance under the longer transmission distance situation is limited.

People have proposed several different methods and have solved these problems, but these methods possess skills usually and/or the cost defective.These solutions comprise that (a) uses dispersion compensator, and dispersion compensator is expensive usually, complicated and loaded down with trivial details, need customize each optical fiber span usually.(b) use external modulation continuous wave (CW) DFB that is coupled to the Mach-Zehnder modulator.It is zero warbling that this kind combination can show actual in some cases, but for except that the application of a few special common small size, high cost makes this kind solution surdimensionnement and too expensive.(c) use Electroabsorption Modulated Laser (EML), its have margin of operation narrow, need complicated predistortion circuit reduce big relatively intrinsic harmonic distortion, and carrier-to-noise than (CNR) on the low side (because of optical output power low relatively) shortcoming.

The expensive confirmation of optical launcher solution mentioned above is to cause developing the some kinds of key factors that strengthen the technology of direct modulation D FB performance.These methods generally include a kind of or combination in the following technology: (i) electronics pre-distortion technology, its be used to revise second-order distortion deterioration (for example, referring to the 5th, 436, No. 749; The 4th, 992, No. 754; The 5th, 227, No. 736 United States Patent (USP)s) and revise third order distortion (for example, referring to the 5th, 172, No. 068 United States Patent (USP)).The major defect of these technology comprises the expense increase and need customize the distortion correction that adapts in various degree in manufacture process.(ii) the optics injection locking technique wherein injects one from laser with light from a main laser, then described output from laser is locked to main laser.Yet, this method is very limited in commercial successful situation, because its cost height and complexity are (for example, referring to " the semiconductor laser intermodulation distortion are to the dependence of fiber lengths and by reduce (the Dependence of Semiconductor LaserIntermodulation Distortion on Fiber Length and its Reduction by Optical InjectionLocking) of optics injection locking to it " that the people showed such as H.Sung, Conference Proceedings, Paper WE2 10, the 186-200 pages or leaves).(iii) optics linearization technique wherein uses an external optical element that DFB is carried out optics and strengthens (for example, referring to the 6th, 538, No. 789 United States Patent (USP)s).

Therefore, in affiliated technical field, need a kind of distributed Bragg reflector laser diode with improvement that low analog distortion and/or available low relatively cost obtain.

Summary of the invention

The present invention relates to have design, encapsulation and the manufacturing of direct modulation system analog external cavity laser (ECL) of the cost-performance ratio of improvement, this direct modulation system analog external cavity laser (ECL) is used for transportation simulator and half module and intends (for example quadrature amplitude modulation (qam)) signal, uses in particular for broadcasting, digital synchronous broadcasting and Narrowcasting (QAM).

In addition, some embodiment of the present invention relates to the design of direct modulation system simulation ECL, and this direct modulation system simulation ECL side by side (i) controls warble (from the extremely low paramount value of value); (ii) has low intermodulation distortion (second order and three rank); And low relative intensity noise (RIN), this can be provided for the high-performance of transmission of analogue signal in 1550 wave-length coverages, low-cost device, method and/or system.

The invention further relates to and comprise package design and encapsulation standard (especially in the industry commonly used the encapsulation of 14 pin butterflies), and wherein use one to make up outer laser chamber with an integrated high coupled lens and the Fiber Bragg Grating FBG element of light source (Fabry-Perot (FP) chip) termination, all these devices all are installed on the same solid substrate.This kind method provides long-term packaged stability, and this is especially favourable in aaaanalog transmission system.

The invention further relates to and comprise and be used to improve the coupling efficiency in this chamber between FP chip and the optical grating element, reduce the design and the method for the unexpected reflectivity in the simulation ECL chamber simultaneously.

The invention further relates to and be used to reduce the method for reflection light quantity that is coupled back in the chamber of simulation ECL.The luminous energy that suppresses to be reflected be coupled back most important for the performance of simulating ECL in the transmission system in the chamber.Be used for realizing the method that catoptrical height suppresses is included in the pigtail of simulation ECL and/or the suitable design of cavity reflection face reflectivity outside and incorporate a coaxial optical isolator into.

The invention further relates to by correct design reflectivity external reflective element and by ECL being carried out proper temperature and control and strengthen and utilizes and simulate so-called distortion bust among the ECL.

The invention further relates to design and implement to be used to suppress stimulated Brillouin scattering (Stimulated BrillouinScattering, SBS) in the chamber and the chamber outside method the two, if stimulated Brillouin scattering is reduced inadequately, can seriously limit the amount that to inject the luminous power in the optical fiber.

The invention further relates to design and implement to be used for the tuning and stable industry standard to dense Wave division multiplexing (DWDM) system of the power output of simulation ECL with interior and can not sacrifice the desired distortion of simulation ECL, warble and the technology of RIN characteristic.

The invention further relates to the method that is used to reduce so-called frequency ramps, described frequency ramps shows as before the link of higher degree and distortion behind the link, and it can influence the higher frequency passage of injecting in the optical fiber.

The invention further relates to and be used for simulation ECL is designed to be able to the method that success comprises known predistortion and electronic dispersion compensation (EDC) technology, utilize the distortion and the range performance of reflector of these simulations ECL with further raising.

The invention further relates to the Bragg grating that is used to use in the fibre core that is formed at various optical fiber and make the method for simulation ECL, described various optical fiber comprise that the no chromatic dispersion of standard is offset monomode fiber (for example Corning SMF-28), dispersion-shifted monomode fiber, polarization-maintaining single-mode fiber, reaches graded-index and step index multimode fiber.

According to the of the present invention various embodiment that hereinafter described in detail, can obtain these and other for the conspicuous advantage of person of ordinary skill in the field.

Description of drawings

Graphic and not drawn on scale herein and each assembly that is illustrated one graphic in and each relative size between graphic and ratio just schematically but not draw in proportion.

For ease of understanding, use identical reference numerals to represent each graphic common similar elements in possible place.

By graphicly considering hereinafter to describe in detail in conjunction with following, can more easily understand technology of the present invention, graphic in:

Fig. 1 illustrates a typical ECL structure with block diagram form;

Fig. 2 is the schematic diagram of an ECL, and this ECL is configured with: (a) Fiber Bragg Grating FBG, and the Bragg grating that (b) writes in the waveguide on PLC;

Fig. 3 is the schematic diagram of an outside cavity gas laser;

Fig. 4 is the curve chart that illustrates ECL emission wavelength one TEC temperature relation, its expression moding zone;

Fig. 5 is the curve chart that illustrates near the spectral response of an ECL moding zone, and it also illustrates in the peak value transition of temperature when fading to 19.8 ℃ for 20.2 ℃;

Fig. 6 is for illustrating the curve chart of slope efficiency-bias current relation (it is the first derivative of the L-I curve of ECL);

Fig. 7 one is assembled on the same substrate chip and grating to guarantee to make the schematic diagram of the ECL that stability is improved.Two attachment points can make the FBG section keep bearing a controlled stress (compression stress or tension stress), to obtain improved performance under the direct modeling modulation case;

Fig. 8 is the distortion curve figure of an ECL embodiment, and it comprises a distortion bust;

Fig. 9 is the second-order distortion (for example IMD2) and the curve chart of warbling and changing with temperature range between each moding in the FBG design implementation example of a simulation ECL.This figure illustrates and can select the required level of warbling by suitably selecting working temperature (being the TEC temperature).Illustrate experimental result among the figure.

Figure 10 is in one-sided butterfly curve (distortion bust) therein and the maximum example that aligns of warbling, second-order distortion (for example IMD2) (lefthand vertical axis) and warbling with the curve chart of temperature range variation between each moding in the FBG design implementation example of a simulation ECL.This figure illustrates numerical simulation results.

Figure 11 is the curve chart that the FBG reflectance curve changes with the wavelength span." knee " shape spectrum curve helps making as shown in figure 10 OSBDP (distortion bust) and the high region alignment of warbling.

Figure 12 is the schematic diagram of ECL multi-wavelength array, and this multi-wavelength array comprises: (a) a plurality of different optics output beams; And (b) a plurality ofly be multiplexed in the single strand optical fiber or be multiplexed to output beam in the last waveguide of PLC;

Figure 13 is by using an external phase modulator to come simulation ECL is used the schematic diagram that SBS suppresses as a Bragg grating that is written in the polarization maintaining optical fibre (PMF) in this figure illustrated embodiment;

Figure 14 one has the schematic diagram of the simulation ECL of a coaxial optical isolator in pigtail;

The CSO that Figure 15 illustrates simulation ECL tilts and uses more wide bandwidth FBG to its improvement of carrying out.CSO is tilted in and is defined as the poor of under the intermediate frequency of 314.5MHz and the high frequency situations at 547.5MHz CSO herein;

Figure 16 illustrates CSO inclination and the use of ECL under high frequency (547.5MHz) situation and warbles FBG to its improvement of carrying out;

Figure 17 is the schematic diagram of a simulation ECL, and this simulation ECL has the optical isolator of integration mutually and the filter of the pigtail of twisting with the fingers into described simulation ECL.This filter can reduce spontaneous emission;

Figure 18 is the decay and the chromatic dispersion-wavelength relationship curve chart of standard single-mode fiber and dispersion-shifted fiber.

Embodiment

After considering hereinafter explanation, the person of ordinary skill in the field will clearly realize that teaching content of the present invention can be used for design at an easy rate, makes, encapsulates and/or use outside cavity gas laser (ECL), especially simulates ECL.

Technology described herein relates to analog external cavity laser, comprises being used for designing, encapsulate and improve for being used to simulate and the technology of the performance of the ECL of CATV optical fiber telecommunications system.This application only is an example but not as limiting, because system as herein described, technology, process, device and material also can be applicable in the other field.Simulation ECL as herein described is direct modulation system lasing light emitter, and it is used for the device of simulated optical transmission and system with other and compares and have tangible advantage.These advantages are included in distortion and (for example) aspect of warbling has higher performance, cost step-down and has the design margin of improvement.

One typical ECL comprises a laser diode chip 200, and laser diode chip 200 has a high reflection surface that is coated with high reflectance (HR) film 202 usually, and is transmittance to the light that described laser diode produced but is coated with the apparent surface of an antireflective (AR) coating 201 usually.As shown in Figure 1, combined with a bulk of optical feedback element 103, form an optical delivery function F (λ).Optical delivery function F (λ) is generally a grating-be called sometimes Bragg grating, and in fact be also used as a speculum and a filter, form the output of laser with the light that some is incident thereon 104 reflected back laser diode chips 200, the another part of transmission simultaneously light 105.The laser that is produced by ECL rebounds between high reflection (HR) side (promptly relative with AR coating side) of laser diode 202 and grating 103 back and forth, forms laser cavity thus.

According to some embodiment, the present invention includes an outside cavity gas laser (ECL), wherein said grating is formed in the optical fiber (and thereby be often referred to as Fiber Bragg Grating FBG (FBG)), is expressed as 203 shown in Fig. 2 (a).In other embodiments, described grating can be formed in the slab guide on the planar lightwave circuit (PLC), shown in 203 among Fig. 2 (b).In other ECL embodiment, the optical delivery function can comprise body grating, acousto-optic filter, an etalon type thick film or a Thin Film Filter that is built in glass, semiconductor or the other materials.In other embodiments, described grating can be formed at semi-conducting material (indium phosphide for example, InP) in.Other ECL embodiment comprise use one tunable formula grating, for example wherein can use and come tuning optics propagation function: make grating carry out spatial movement (for example using MEMS (micro electro mechanical system) (MEMS)) with inferior technology, or use a RF signal and come tuning one optical delivery function based on acousto-optic, perhaps use the tunable formula filter of tuning based thin film of stress or thick film, perhaps use one be written in the semiconductor chip or on tunable formula grating, and other technologies.These embodiment can comprise but needn't comprise a beam-shaping element between luminescence chip and external reflection surface.

Simulation ECL as herein described normally uses Fiber Bragg Grating FBG (FBG) to be illustrated as the exocoel of reflecting element in conjunction with one.Yet this is a way of example but not as limiting, because technology described herein can be easily in conjunction with utilizing the exocoel of other reflecting elements to use, this easily knows for the those of ordinary skill in the affiliated technical field.

The lasing light emitter module is given in the practical communication system (or other application) usually, and wherein laser module can stand broad temperature range (for example-20 ℃ to+75 ℃).Because operation wavelength can vary with temperature usually sensitively, thereby the known practice is to provide temperature sensing and temperature control device to keep a narrower operating temperature range (such as about 15-35 ℃) in the module package environment in module package.A kind of widely used cooling device is thermoelectric (al) cooler (TEC).

Embodiments of the invention comprise the analog external cavity laser that advantageously designs and form according to several standards.Dispose and use this kind standard to comprise some aspects of the present invention.Compare with common prior art device, formed simulation ECL can realize several advantages.

The encapsulation of ECL is a pith of whole ECL system.Some embodiment of the present invention comprises the design standard that is used for the ECL encapsulation.By illustration but not limiting mode, embodiment described herein relates to a kind of simulation ECL based on FBG, and it comprises that one is integrated in the lens at the place, tip of the optical fiber that contains FBG.

Simulation ECL according to certain embodiments of the invention comprises a combination of carrying out preferable selection to following: Fabry-Perot (FP) booster element (or laser diode chip, 200), the exocoel design reaches the correct adjusting to gap between optical module that contains grating and the laser diode chip, and wherein said gap adjustment can influence optical coupled.According to some embodiment of the present invention, in the ECL design, also considered the loading condition of diffraction loss and favourable imbalance.Generally speaking, favourable CSO level of distortion can be depending on the FP chip performance or has amplitude and specific and the design of the exocoel of phase curve.Therefore, comprise some constraint usually according to certain embodiments of the invention exploitations and the design standard used to the FP chip.

In 300, design and encapsulation standard have been developed, to solve encapsulation sensitiveness and FP chip and the coupling that comprises the assembly of grating 301 according to experiment and the two some embodiment according to the present invention of computer model (Fig. 3).Typical standard comprises following standard:

The Fabry-Perot booster element advantageously provides the constraint of effective length (La among Fig. 3)-(μ m=micron=10 between about 300 μ m and about 600 μ m ^-6Rice).

The lower limit of the length L a of FP chip depends primarily on the linearity of the optical output power of ECL and the relation curve of laser injection current (so-called L-I curve) and Fabry-Perot chip and responds in the adiabatic chirp of related frequency range (for example for CATV and use speech based on the Optical Fiber Transmission of RF and be in and be up to about 10-3, the 000MHz scope is interior).Because the adiabatic chirp response is generally the function of 1/La, thereby tends to follow this kind relation.The upper limit of La depends primarily on the temperature span between each moding, and described temperature span is directly related with the FP chip length.

Temperature span between each moding depends upon many factors, comprises the length and the of such little moment ground of FP chip, and optical grating element is with respect to the relative position of chip gain.When ECL TEC variations in temperature, the moding meeting shows as the increase that increases the emergent ECL emission wavelength of mode with an approximate step after a range of linearity, as shown in FIG. 4.The moding zone presents a hysteresis effect, obtains different wavelength-TEC thermal tracking thus, and this depends on that temperature is upwards or to lower swing.For example, one is built-in with the ECL based on FBG that an effective length is about the InGaAsP/InPFP chip of 500 μ m shows about 8 a ℃ temperature interval between each moding, as shown in FIG. 4.Make ECL in moding location or not good usually near the moding regional work, this is because the output of simulation ECL has potential unsteadiness.Can comprise one modestly away from moding position about 1 ℃ or bigger temperature working point " margin of safety ".Thereby the free space/nargin with ECL simulation encapsulation of 500 μ m chip length is reduced to 5-6 ℃ thus, and for a longer chip, is reduced to one even littler nargin.Therefore, an aspect of certain embodiments of the invention is to select length described booster element chip and whole cavity, so that can reach a working temperature window of several ℃ at least between each moding.

High reflectance on the Fabry-Perot booster element chip (back facet) coating has a reflectivity that is higher than about 75-95% usually, and AR coating (front facet) has the reflectivity less than about 0.05%.Some embodiment of the present invention has the have angle waveguide of (being about the 6-10 degree usually) location of front facet with respect to described booster element chip, has loosened thus front faceted AR coating technology requirement.

Required level of distortion and usable temp nargin are depended in the constraint of AR coating usually, and this depends upon the value of AR coating.The temperature width that temperature interval between each moding of 500 μ m chips only is about 8 ℃ and moding zone is very little-for being lower than about 0.05% AR, be about 0.15-0.2 ℃.If the AR coating does not have sufficiently high quality (for example＞0.07%), then the temperature width in moding zone increases to about 0.5-0.7 ℃, and this mainly is to cause because of the competition between each mode of laser in the hysteresis region strengthens.When passing a moding zone from stability region scanning ECL temperature, the line of ECL fades to multiple spectrum mode for the single mode that can have unacceptable low side mode suppression ratio (SMSR) usually certainly, as shown in FIG. 5.When the AR coating is lower than about 0.05% reflectivity, can be on distance moding border ± 0.2 degree is with the single mode operation of interior realization SMSR greater than about 35dB.

Exocoel design requires FP to have high-performance usually, particularly low current leakage, high slope efficiency, little α factor (less than about 4) and adiabatic chirp value.One one of them phenomenon with high efficiency FP chip of low current leakage is that the variable quantity compared with its threshold value of differential resistance measured under the high bias currents situation is very little.Other requirements to the FP chip stem from the following fact: simulation ECL requires to have high optical coupling efficiency usually between described chip and exocoel reflecting element.Therefore, be preferably and use a kind of buried type heterojunction (BH) type with symmetrical far field beam profile (for example, have less than about 1.2 light beam ovality).This kind far field beam profile allow one have high coupling efficiency (about for example about 56-70%) based on the simulation ECL of FBG in use optical fiber integration lens.

The ECL that parameter for example cited herein usually can actual package has preferable amount of available power.

Relating on the other hand by a kind of chamber design of certain embodiments of the invention obtains low distortion simulation ECL, and this chamber design has one and strengthens factor (α factor) less than about 4 line width at the wavelength place corresponding to FP chip gain peak.

Except the limited value that the FP with the gain peak place warbles the α factor relevant, also benefit from so-called blue imbalance according to the distortion performance of the simulation ECL of certain embodiments of the invention.Blue imbalance is the side-play amount between the ECL of low wavelength side (blue side) the emission optical maser wavelength of FP chip gain peak.Blue imbalance can make the α factor reduce with wavelength, and this helps obtaining lower distortion in simulation ECL.Typical blue misalignment rate is in the scope of the about 20-50nm of distance gain peak.For being suppressed at FP gain peak place competition emission laser, need to use a high-performance AR coating usually, the AR coating is less than about 0.05% usually.

For reducing level of distortion, the exocoel design should be avoided optical signalling coating (HR/AR) the FP chip of hanging oneself is coupled to high Q resonant cavity.In other words, make grating reflection rate (R) keep below about 25% and can obtain favourable chamber design usually.

Simultaneously, if the optical grating reflection rate becomes very little, R～5% for example, then described chamber can and become unstable along with the mode competition aggravation usually, and can become extremely difficult to the encapsulation in this kind chamber.Therefore, favourable R scope is approximately 5%＜R＜25%.

Favourable situation be increase and make great efforts to make light to hang oneself to be coupled into optical grating element (for example be monomode fiber in based on the ECL situation of FBG to coatings (HR/AR) FP chip, perhaps in based on the ECL situation of PLC for slab guide, perhaps can constitute the combination in any of FP chip, coupling optical device and the external resonant cavity of an exocoel) coupling efficiency (C) maximization.Can penetrate the beam quality of FP chip and realize the maximization of coupling efficiency by design coupling optical device as shown in Figure 1 correctly by improvement.

The approximate lower limit of minimum coupled power depends on two factors usually: to the constraint of simulated laser device available horsepower (usually＞7dBm) and the standard of coupling efficiency C as herein described-this can obtain effective ECL " front facet " reflectivity R _Eff=C ²* R _MaxIf C～0.7 (for common actual embodiment), and R=15%, then R _Eff=7.4%, this shows that the chamber is more weak and has high FP mode competition.These Considerations make us draw minimized some condition of AR coating reflectivity that makes once more.The last binding occurrence (Cmax) of coupling efficiency then depends on the practicality and the sensitivity to calibrating of coupling optical device.

The integral lens design is an important embodiment, and it can provide machinery and regulation pull-out stability in the ECL encapsulation.

According to some embodiment of the present invention, some standard is also advantageously followed in the design of described exocoel (outside FBG or be positioned at grating on the PLC substrate).It is at single mode SMSR＞35dB in service that one standard is arranged in these standards.

Other standards comprise: mould separation delta λ sp (as ECL bias current=Ibias～Ith, being cold chamber during near the Laser emission threshold value) is to preferable being in 0.5＜Δ λ sp/BW＜1.3 scopes of ratio of the bandwidth (BW) of Bragg grating.

This kind standard as herein described trends towards forming a high degree of discrimination and avoids mode competition between a main mould and each secondary mould (promptly producing the single mode operation of SMSR＞35dB).Simultaneously, this kind standard can be used as the optimization parameter of a reality in the process of assembling simulation ECL chamber.

Relation between the so-called effective length Leff of passive length in ECL chamber (Lp among Fig. 3) and ECL grating makes it possible to according to being used for designing effectively warbling of exocoel.The Leff of one so-called low light level grid (R is less than about 15%) is the function of grating bandwidth and reflectance curve.

For outside FBG or be positioned at Bragg grating on the PLC platform for the two, the Sidelobe Suppression (SLC) of grating is advantageously surpassed about 15dB, so that in the temperature interval of 1 ℃ of distance moding temperature T h, provide＞SMSR of 35dB.

An example according to the FBG of certain embodiments of the invention design is an apodization grating as an actual embodiment.Still make the designer of simulation ECL make a selection with the relevant standard of requirement of warbling to some relation between passive length and the ECL effective length.

Another aspect of the present invention relates in ECL and to utilize and adjust regulation drop-out, so that reduce second order under the direct modeling modulation case and/or third order distortion, obtain a required level of warbling simultaneously.In ECL design according to certain embodiments of the invention, the regulation drop-out parameter X _DL=(λ-λ p)/BW (wherein λ p is that the peak wavelength and the λ of grating curve are the laser emission wavelength of ECL) plays an important role in ECL distortion mechanism (second order CSO and 3 rank CTB the two).When the exocoel of assembling ECL, these parameters are generally the sensitivity function in gap between the effective reflectivity plane of the facet that is coated with AR of FP chip and grating.

The modeling of distortion mechanism and the experiment of analysis and reality are shown, reflectance curve for arbitrary in fact type of optical element F (λ), all can obtain to depend upon about slope efficiency (it is the first derivative of L-I curve shown in Fig. 6) unique feature of bias current, this can provide minimum distortion in the temperature range between each moding position.This feature depends upon a regulation pull-out effect that changes with bias current and temperature owing to the effective reflectivity of the threshold current of the following fact: ECL and grating.Be the distortion that obtains to reduce, certain regulation pull-out state of preferable use, and this kind regulation pull-out state can make the slope efficiency curve have a certain character shape.When the gradient of efficiency curve is reaching peak value, increasing with bias current then and reach minimum substantially at target light power output place, and when raising once more subsequently, can obtain usually to reduce and basic minimum distortion around the threshold current.An aspect of certain embodiments of the invention relates to and use this kind feature when design, structure and assembling simulation ECL.

This kind feature of slope efficiency curve is responsive to regulation pull-out usually.Therefore, for guaranteeing the mechanical stability of ECL in environmental change, a chip and a grating based on the ECL of FBG advantageously is assembled on the same substrate, as shown in FIG. 7.

An aspect of certain embodiments of the invention relates in the part as the assembling process of simulation ECL when described exocoel is calibrated and measures and monitor second-order distortion (CSO or IMD2 or IP2) on one's own initiative.When obtaining required level of distortion, with bulk of optical feedback element (F (λ)) fix in position.For example, under ECL situation, also use fixing point as shown in Figure 7 to be fixed in place subsequently the FBG calibration based on FBG.This kind technology can make fine ratio of product be improved usually and the consistency between each ECL device is improved.In addition, the monitoring distortion and/or the low cost that can realize device of warbling customize (if needs) in assembling process.

With regard to second-order distortion, simulation ECL has one by the regional unique pattern formed of an ECL operating temperature, and in this ECL operating temperature zone, under all carrier frequencies, second order and third order distortion are all less.This specific character is called " one-sided butterfly distortion curve " (OSBDP) or " distortion bust ".This kind distortion bust come across usually one be about in 1-2 ℃ the narrow temperature range of operation Δ T-this temperature range of operation occurs near the moding position usually, as shown in FIG. 8.According to the simulation ECL of certain embodiments of the invention usually under arbitrary operating temperature but have under the situation that is starkly lower than DFB of warbling with DFB CSO performance quite or better CSO.This makes simulation ECL laser very attractive for broadband and arrowband simulation application (CATV, QAM based on the optical fiber of RF, reach other application), and transmission range is obviously increased and expanded application, and for example optical fiber is registered one's residence/residence (FTFH/P).

Relating on the other hand with a kind of meeting of certain embodiments of the invention provides the mode of the level of warbling improvement, basic best to design and adjust and warble under required distortion performance situation, and it is high to being enough to suppress SBS but not excessive so that the maximum magnitude of restriction institute transmission of analogue signal wherein to warble.Possess an ECL with low distortion level and can't guarantee on the analog optical fiber link, to obtain enough signal performances automatically, because low warbling can interact with the nonlinear effect in the typical optical fiber, thereby makes SBS and so-called dual Raleigh scattering (interaction noise) become the limiting factor of link performance.In addition, the use RF dither of having developed at DFB and the external modulation source existing method that suppresses SBS may be not enough to suppress the SBS based in the ECL reflector.A kind of method that solves based on the SBS problem of the reflector of ECL is to increase the level of warbling, keep low distortion simultaneously.One is suitable for obtaining the high relatively simulation ECL that warbles, keeps the embodiment of low distortion and low RIN to shorten cavity length by the post-boost phase Lp that reduces among Fig. 3 simultaneously.

Fig. 9 (experimental result) and Figure 10 (simulation computer model result) show two kinds of different designs of a simulation ECL, wherein can be by ECL being moved select a certain level of warbling under the temperature of correctly choosing, keeping low distortion (second order and three rank the two) simultaneously.The invention still further relates to utilize and design and have the simulation ECL that (i) can adjust the level of warbling of warbling and (ii) increasing.Adjustable warbling makes the user can " dial in " level of warbling that is more suitable in its application.For in simulation ECL, obtain high relatively warbling (＞keep low distortion 35MHz/mA), simultaneously, the optical grating element that designs ECL according to one of following guide rule (includes but not limited to FBG, based on the waveguide optical grating among the ECL of PLC, body grating is based on sound-optical grating): (i) be designed to a chirp grating; (ii) one has the spectrum curve shown in Figure 11 grating of (being called " knee " spectrum curve); (iii) one has the grating of wherein introducing the spectrum curve of warbling by outside approach (for example gradient that is formed by stress).

Also can use the electronics dithering to replace or conduct adding to ECL to the high relatively level of warbling.A kind of technology is that simulation ECL input is used triangular pulse or the high relatively tone of a class frequency, and wherein total warbling depends primarily on transient state component.

Certain embodiments of the invention relate to simulation ECL on the other hand based on FBG, wherein be to improve ECL to be positioned on the grid that standardization is Wave division multiplexing (WDM) system regulation, under mechanical stress (tension stress or compression), FBG assembled and fix in position for the performance of direct modeling modulation and/or for emission wavelength is tuned to.The mechanical stress that is applied to FBG be used to adjust simulation ECL distortion, warble and/or emission wavelength.As an example, in Fig. 7, make the FBG section keep bearing controlled stress by using two permanent joints (for example permanent joint that forms by soldering, laser welding or epoxy).

Relating to simulation ECL design on the other hand and being built into of certain embodiments of the invention makes its emission wavelength be centered at or be locked to or is adjacent to industry standardization ITU wavelength grid, so that described ECL can be used in Wave division multiplexing (WDM) system, a plurality of independent light beams of carrying different information respectively that are in different wave length are injected in one optical fiber.The optical grating element of typical simulation ECL described herein can be designed to have a following peak wavelength: correct regulate that ECL TEC temperature is warbled with improvement and distortion after, the emission wavelength of ECL remains in the ITU wavelength grid tolerance.

Another aspect of the present invention relates to using monolithic and/or mixed product to assign to design and making up one simulates the ECL array.But each the ECL element in this array is all launched a predetermined wavelength and separate modulation.Element in this array can but needn't share same temperature controller.One exemplary embodiments of this simulation ECL array is shown among Figure 12.The example that makes up this ECL array is included in the waveguide array on the PLC and uses a FBG array or a grating.Multi-wavelength from this array is exported an optically multiplexed device that passes among Fig. 2 (b).

Certain embodiments of the invention relate to a kind of ECL on the other hand based on FBG, wherein FBG is formed in the polarization maintaining optical fibre (PMF).This embodiment makes the noise of direct modeling modulation system ECL be lower than the ECL that is built-in with standard single-mode fiber.In addition, the ECL that is built-in with PMF can be used as high-quality low noise CW lasing light emitter in an external modulation formula simulating emitter.Except that controlled polarization, the ECL that is built-in with PMF also provides narrow live width, low relative intensity noise (RIN) simultaneously, and high optical output power-this can be coupled in the external modulation member subsequently.

Certain embodiments of the invention relate to the analog-modulated formula ECL that uses a Bragg grating that is positioned at a PMF optical fiber pigtail to make on the other hand, described Bragg grating and is widely used in phase-modulator (for example lithium niobate modulator) interaction of the SBS in the inhibition analogue system in the prior art.This is shown among Figure 13.

The invention further relates to and comprise package design and encapsulation standard (especially in the industry commonly used the encapsulation of 14 pin butterflies), and wherein use one to make up outer laser chamber with an integrated high coupled lens and the Fiber Bragg Grating FBG element of light source (Fabry-Perot (FP) chip) termination, all these devices all are installed on the same solid substrate.This kind method provides long-term packaged stability, and this is especially favourable in aaaanalog transmission system.

The invention further relates to and comprise and be used to improve the coupling efficiency in this chamber between FP chip and the optical grating element, reduce the design and the method for the unexpected reflectivity in the simulation ECL chamber simultaneously.Be to use a lenticule that is made in the place, tip of the optical fiber that contains described grating based on the embodiment of the simulation ECL of FBG.The embodiment of this kind optical fiber lens comprises the hemispherical lens and the double curve shape lens of a convergent.

The invention further relates to and be used to reduce the method for reflection light quantity that is coupled back in the chamber of simulation ECL.The luminous energy that suppresses to be reflected be coupled back most important for the performance of simulating ECL in the transmission system in the chamber.Be used for realizing the method that catoptrical height suppresses comprised as shown in figure 14 and incorporate a coaxial optical isolator at pigtail.

The invention further relates to by correct design reflectivity external reflective element and by ECL being carried out temperature and control and strengthen and utilizes the distortion bust of simulating among the ECL.

The invention further relates to design and implement to be used to suppress stimulated Brillouin scattering (Stimulated BrillouinScatiering, SBS) method in the chamber, if stimulated Brillouin scattering is reduced deficiently, can seriously limit the amount that to inject the luminous power in the optical fiber.SBS suppresses to be based on the modulation to the effective path length of light in the chamber in the chamber among the simulation ECL.Some embodiment that SBS suppresses in the simulation ECL lumen comprise (i) be arranged near the reflecting element (for example FBG) one or on piezo-electric pick-up or electrostatic element apply the signal of telecommunication once modulation; (ii) modulate the position of the reflecting element of exocoel; A dither signal of telecommunication (iii) superposes on the booster element chip of simulation ECL.

This simulation ECL further relates to the method that is used to reduce so-called frequency ramps, and frequency ramps shows as before the link of higher degree and distortion behind the link, and it can influence the higher frequency passage of injecting in the optical fiber.The two method of a kind of overall distortion that is used for improveing simultaneously simulation ECL and frequency ramps is the chromatic dispersion character that reduces to be used as at exocoel the optical grating element of reflecting element.The embodiment of the invention based on the ECL of grating comprises a combination of using a kind of following technology or one or more following technology: (i) design under full width at half maximum (FWHM) (FWHM) situation, have a big relatively bandwidth grating (for example, the FBG of optical curve bandwidth in about 220-450pm scope, wherein pm=micromicron=10 ^-12Rice), as seen from experimental data shown in Figure 15; (ii) use the reflecting element of non-apodization grating as exocoel; (iii) use the FBG that warbles with suitable gradient direction, so that the chromatic dispersion in the cancellation grating, experimental data is shown as shown in Figure 16.

The invention further relates to and be used to improve simulation ECL design, utilize the distortion and the range performance of the reflector of these simulations ECL with further raising so that can successfully comprise the predistortion extensively addressed in the prior art and the method for electronic dispersion compensation (EDC) technology.

The invention further relates to the Bragg grating that is used to use in the fibre core that is formed at various optical fiber and make the method for simulation ECL, described various optical fiber comprise that the no chromatic dispersion of standard is offset monomode fiber (for example Corning SMF-28), dispersion-shifted monomode fiber, polarization-maintaining single-mode fiber, reaches graded-index and step index multimode fiber.

The invention further relates to the spontaneous emission noise that reduces to come self simulation ECL institute emitting output light bundle.Suppress spontaneous emission meeting improvement transmission performance, especially when in link, having the optical amplifier of cascade.An embodiment relates to a coaxial filter (for example Thin Film Filter) is twisted with the fingers into simulation ECL pigtail.Another embodiment is as shown in figure 17 with in the filter sheet integrated isolator used in the pigtail of simulating ECL.

Another aspect of certain embodiments of the invention relate to direct modeling modulation system ECL in the 1310nm wave-length coverage of emission wavelength wherein (include but not limited to based on FBG ECL, the grating in the PLC waveguide, body grating, and sound-optical grating).Direct modeling modulation system 1310nm ECL all possesses advantage in following two kinds of transmission medium situations: the on-dispersive deflection optical fiber of dispersion-shifted fiber and standard.Under the dispersion-shifted fiber situation, the low chirping characteristics of ECL can improve range capability by the interaction that alleviates non-zero dispersion in laser chirp and the optical fiber and reduce the link distortion.This is similar to the advantage that is obtained when using 1550nm ECL in standard SMF.

For the 1310nm wave-length coverage in standard (on-dispersive skew) monomode fiber, optical fiber dispersion is actual to be zero, as shown in figure 18.Thereby warbling in the laser be not only acceptable, and be needed for reducing the nonlinear effect of introducing because of the optical fiber of high transmit power level.Direct modeling modulation system ECL can provide the inherent distortion performance of enhancing, but for offsetting low (stimulated Brillouin scattering (the StimulatedBrillouin Scattering that warbles when in SMF, launching high luminous power, SBS) and the Raileigh backscattering) to the influence of analogue transmission, need dither method (including but not limited to electric and mechanical technique) usually.

The method that another kind is used to reduce the nonlinear effect of 1310nm optical fiber is direct modeling modulation system ECL to be designed to launch one depart from the zero dispersion point of SMF or approach the wavelength (referring to Figure 18) of zero dispersion point.In other words, the emission wavelength of ECL is designed wittingly and is built into be in the 1320-1350nm scope or be in after the water peak value (promptly＞1390nm).

Another aspect of certain embodiments of the invention relates to the optical launcher that comprises direct modeling modulation system ECL, wherein these reflectors can at the distortion in the field and/or warble tuning in addition, and described tuning can enforcement by the network management software away from a central office (CO) or network operation center (NOC).In other words, can system equipment install or network is prepared or maintenance process in to the distortion of simulating emitter and/or warble level and/or optical output power carry out tuning or adjust with obtain an improvement of being adjusted at concrete system link or basic best carrier-to-noise than (CNR) (and other system parameterss).Promptly do not need to purchase new reflector group thus basically and eliminated relevant delay and cost.An embodiment of tunable formula simulating emitter is included in the manufacture process of reflector to look into table one and is programmed in the transmitter memory.This looks into " contour map " that comprises desired properties parameter (for example distortion, warble, wavelength shift, power output-TEC temperature) with table.Then, the user can use software command to programme to look into showing by visit and from institute and select to optimize link performance.

Another aspect of certain embodiments of the invention relates to the direct modeling modulation system ECL of tunable wave length.The embodiment of the simulation ECL of tunable wave length includes but not limited to that (i) for for the ECL of FBG, carries out tuning (for example using a piezo-activator) to FBG; (ii) form and tuning grating, wherein come tuning and the selection emission wavelength by optionally control the RF signal combinedly with a removable speculum by a RF signal that is applied to sound-optical material; (iii) use a tunable formula filter based on etalon.

Although show in detail in this article and each embodiment that comprises teaching content of the present invention has been described,, the person of ordinary skill in the field still comprises the different embodiment of these disclosure yet can easily dreaming up many other.

Claims (18)

1, a kind of analog external cavity laser, it comprises:

A) light source, it has a reflectivity back facet, a transmittance front facet; And,

B) a local reflex feedback element, it matches with described reflectivity back facet and forms a laser cavity; And,

C) one or more temperature controllers, it makes the operating temperature of described laser keep departing from least some degrees centigrade of modings.

2, analog external cavity laser as claimed in claim 1, wherein said reflectivity back facet have one and surpass about 75% reflectivity.

3, analog external cavity laser as claimed in claim 1, it comprises that further one is positioned at the antireflecting coating on the facet of described front, wherein said antireflection coatings has one less than about 0.05% reflectivity.

4, analog external cavity laser as claimed in claim 1, wherein said light source are a Fabry-Perot booster element, its have one from about 300 microns to about 500 microns effective length.

5, analog external cavity laser as claimed in claim 1, wherein said feedback element are an optical fiber Bragg (Bragg) grating.

6, analog external cavity laser as claimed in claim 1, wherein said feedback element have one from roughly 5% to 25% reflectivity roughly.

7, analog external cavity laser as claimed in claim 1, wherein said light source have the far field flux curve of a symmetry.

8, analog external cavity laser as claimed in claim 1, wherein said laser cavity have one and strengthen factor less than about 4 line width at the wavelength place of the gain peak of described light source.

9, analog external cavity laser as claimed in claim 1, wherein intermode apart to the ratio of the bandwidth of described feedback element from roughly 0.5 to roughly 1.3.

10, analog external cavity laser as claimed in claim 1, the Sidelobe Suppression of wherein said feedback element surpasses about 15dB.

11, analog external cavity laser as claimed in claim 5, wherein said Fiber Bragg Grating FBG are all toe gratings.

12, analog external cavity laser as claimed in claim 5, it further comprises a lenticule on the tip of the optical fiber that comprises described Fiber Bragg Grating FBG.

13, analog external cavity laser as claimed in claim 1, it further comprises one coaxial (in-line) optical isolator.

14, the method for excited Brillouin (Brillouin) scattering in a kind of inhibition one analog external cavity laser, it comprises the effective light path in the described laser cavity of modulation.

15, a kind of method that reduces analog external cavity laser medium frequency inclination, it comprises the chromatic dispersion character of the feedback element that alleviates described analog external cavity laser.

16, method as claimed in claim 15, wherein said method comprise following one of at least:

A) using a big bandwidth Fiber Bragg Grating FBG as described feedback element from 220 micromicrons roughly in the full width at half maximum (FWHM) scope to 450 micromicrons roughly; And,

B) use a non-toe Fiber Bragg Grating FBG of cutting as described feedback element; And,

C) use a chirped fiber Bragg grating as described feedback element with suitable direction, to eliminate the effect of dispersion in the described grating basically.

17, analog external cavity laser as claimed in claim 1, wherein said analog external cavity laser have the imbalance of the blueness to about 50 nanometers from about 20 nanometers.

18, a kind of method of operation one analog external cavity laser, it comprises moves described analog external cavity laser under a regulation pull-out state, so that the gradient of efficiency curve reaches peak value around threshold current, be reduced to roughly with the increase of bias current then and reach a minimum value substantially at required optical output power place, the further increase with described bias current increases then.

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