Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/065—Mode locking; Mode suppression; Mode selection ; Self pulsating
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/40—Arrangement of two or more semiconductor lasers, not provided for in groups H01S5/02 - H01S5/30
  • H01S5/4006—Injection locking
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/005—Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping
  • H01S5/0064—Anti-reflection components, e.g. optical isolators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
  • H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
  • H01S5/06226—Modulation at ultra-high frequencies
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
  • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
  • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
  • H01S5/18355—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL] having a defined polarisation

Definitions

• the present disclosure relates to the use of multimode vertical-cavity surface- emitting lasers (VCSELs) in optical systems and, more particularly to optical injection locking (OIL) techniques for improving the direct modulation performance of multimode VCSELs.
• VCSELs vertical-cavity surface- emitting lasers
• OIL optical injection locking
• Examples of specific applications for the aforementioned laser sources include, but are not limited to, high-speed short-reach fiber-optic networks and radio-over-fiber systems, among others.
• the present inventors have recognized that multimode VCSELs can be attractive components of a laser source because they can be manufactured cost-effectively with larger tolerance and yield than single mode VCSELs.
• the present inventors have also recognized, however, that the multimode nature of the VCSEL can introduce modal competition noise and modal dispersion in the laser source - factors that can prevent these devices from being used for applications that demand high modulation speeds and/or long transmission distance.
• optical injection locking As a technique to improve the direct modulation performance of multimode VCSELs.
• laser sources incorporating optically injection locked multimode VCSELs can be configured as high-speed, low-cost optical transmitters and can function as important components for next generation 100-Gb/s Ethernet and local area networks (LANs).
• LANs local area networks
• the present disclosure contemplates that optical injection locking can be used with a multimode VCSEL having a free-running 1550 nm multimode VCSEL having a 3dB- bandwidth of 3 GHz to yield a 54 GHz resonance frequency and 38 GHz 3-dB bandwidth.
• the techniques are readily applicable to other wavelengths such as 850 nm or 980 nm.
• the aforementioned performance is made possible by leveraging the unique properties of the multimode VCSEL, which typically has spatially and spectrally well- separated modes. As is described in further detail below, this separation facilitates efficient injection locking preferentially to, but not limited to, the fundamental transverse mode.
• the techniques described herein are suitable for a variety of different modulation formats, such as amplitude modulation, phase modulation, or frequency modulation, on either the slave laser or the master laser.
• a method of operating a laser source comprising a single mode master laser and a multimode VCSEL slave laser
• the spatial and spectral coupling of the single mode optical output of the master laser and a target mode of the multimode optical resonator of the VCSEL slave laser are controlled to progress from a relatively mode-matched spatial and spectral coupling to a relatively mismatched spatial and spectral coupling to facilitate optically injected mode locking in the laser source.
• multimode VCSELs typically emit multiple transverse modes, which are at different wavelengths and have different spatial power distributions.
• any of these modes can be selected by matching the optical intensity profile and spectra of the master laser to that given mode.
• the given mode is herein referred to as the target mode.
• a laser source comprising a single mode master laser and a multimode VCSEL slave laser.
• the single mode master laser comprises a wavelength tuning element and a spatial tuning element that facilitate optically injected mode locking in the laser source.
• the injection locking techniques described herein use the single mode master laser to optically lock the multimode VCSEL slave laser, which can be directly modulated.
• the resulting laser source exhibits increased laser resonance frequency and bandwidth, reduced non-linear distortions, and reduced frequency chirp.
• Fig. 1 is a schematic illustration of the spatial progression of the optical output of a single mode master laser relative to the fundamental and first order transverse modes of the multimode optical resonator of a VCSEL slave laser;
• Fig. 2 is a schematic illustration of a laser source comprising a single mode master laser and a multimode VCSEL slave laser
• laser sources 100 comprise a single mode master laser 10 and a multimode VCSEL slave laser 20.
• the single mode optical output 12 of the master laser 10 is spatially and spectrally coupled to the optical resonator 22 of the multimode VCSEL slave laser 20 at an injection ratio P M A STER /P SLA V E that is sufficient to stably injection lock the optical resonator 22 and generate a secondary output beam 25.
• the spatial and spectral coupling of the single mode optical output 12 of the master laser 10 and a target mode of the multimode optical resonator 22 are controlled to progress from a relatively mode-matched spatial and spectral coupling to a relatively mismatched spatial and spectral coupling. This progression facilitates optically injection locking in the laser source 100 and is described in further detail below.
• Fig. 1 illustrates one example of the manner in which the laser source 100 can be operated to progress from a relatively mode-matched spatial coupling, where the single mode optical output 12 of the master laser 10 is spatially aligned with the target mode of the multimode optical resonator 22, to a relatively mismatched spatial coupling, where the single mode optical output 12 of the master laser 10 is primarily coupled to a peripheral spatial portion of the target mode of the multimode optical resonator 22.
• the spatial coupling can be controlled by adjusting the beam spot position of the single mode optical output 12 relative to the input aperture of the multimode optical resonator 22.
• the beam spot position can be adjusted by translating the optical output 12 of the master laser 10 along a dimension that is approximately parallel to the input aperture of the multimode optical resonator 22.
• the beam spot position can be adjusted by steering the output beam, i.e., by altering the angle of incidence of the optical output 12 of the master laser 10 relative to the input aperture of the multimode optical resonator 22.
• the aforementioned translation and beam steering are illustrated schematically in Fig. 1 by directional arrows 15.
• Spatial coupling can be further facilitated by providing the single mode optical output 12 of the master laser 10 with an optical element that is configured to restrict the cross section of the optical output 12 at the input aperture of the multimode optical resonator 22 to a fraction of the cross section of the input aperture.
• an optical element that is configured to restrict the cross section of the optical output 12 at the input aperture of the multimode optical resonator 22 to a fraction of the cross section of the input aperture.
• a lensed or cleaved optical fiber can be utilized to restrict the cross section of the optical output 12 to less than about ' ⁇ of the cross section of the input aperture of the multimode optical resonator 22.
• the cross section of the optical output of the master laser will be between approximately 2 ⁇ m and approximately 10 ⁇ m and the cross section of the input aperture of the multimode optical resonator will be between approximately 7 ⁇ m and approximately 50 ⁇ m.
• Table 1 presents data that illustrates progression from a relatively mode-matched spectral coupling to a relatively mismatched spectral coupling.
• Intermediate spectral coupling values are also illustrated in the table, any one of which could be viewed as a suitable condition for relatively mismatched spatial coupling:
• the injection ratio P MASTER /P SLAVE is measured as a ratio of optical power estimated to be incident on the VCSEL versus the output power of the free running VCSEL.
• the value ⁇ MA S TER- ⁇ sLAVE is measured as the wavelength difference of the master laser and the free running VCSEL.
• relatively mode-matched spectral states need not include the ideal mode- matched spectral state.
• the master laser must merely progress from a spectral state that is mode-matched enough to facilitate mode locking upon progression to the relatively mismatched spectral state.
• Specific wavelength values or relationships for these two types of states will vary depending upon the respective configurations of the master and slave lasers.
• Tables 1 and 2 represent the progression of a master/slave configuration from a mode-matched spatial state to a mismatched spatial state, as is illustrated in Fig. 1.
• Tables 1 and 2 also illustrate injection power ratios and resonance frequencies of the injection locked laser sources as the master laser progresses towards the relatively mismatched spectral state.
• a regime with efficient and stable locking can be found.
• Injection power ratios between approximately -5 dB and approximately 30 dB are likely to be suitable but a variety of injection power ratios are contemplated.
• the injection ratio PMA STER /P SLAVE and the spatial and spectral coupling can be controlled to achieve a resonance frequency exceeding approximately 50 GHz and a 3 dB bandwidth exceeding approximately 30 GHz.
• a single mode to multimode transformer can be used to increase the injection ratio P MAS TE R /P SLA V E and may, for example, comprise a 3-port fused fiber coupler comprising a single-mode fiber port as a master laser input port, a hybrid multimode/single-mode fiber port for in and out coupling the multimode VCSEL slave laser, and a multimode or single mode fiber output port.
• Spectral coupling can be controlled by providing a master laser that is a wavelength tunable laser and by tuning the center wavelength ⁇ MASTER of the single mode optical output 12 of the master laser 10 to a suitable value, typically by a fraction of a nanometer.
• the single mode master laser 10 may, for example, comprise a DBR laser, a DFB laser, a Fabry Perot laser, a VCSEL, or a fiber laser that is either structurally independent of or structurally integrated with the slave laser 20 and can be configured to stably injection lock the multimode VCSEL slave laser 20 via top face, bottom face, or external cavity injection locking.
• the center wavelength ⁇ MASTER can initially be greater than or less than the target mode center wavelength ⁇ s LA v ⁇ of the multimode VCSEL slave laser as it progresses towards the aforementioned mismatched spectral coupling.
• the spectral coupling of the single mode optical output 12 of the master laser 10 should be controlled such that the relatively mode-matched spectral coupling and the relatively mismatched spectral coupling are separated by a wavelength spacing that is merely a fraction of the mode spacing between the fundamental mode and the first order transverse mode of the multimode optical resonator.
• the spectral coupling of the single mode optical output 12 of the master laser 10 can be controlled such that the relatively mode-matched spectral coupling and the relatively mismatched spectral coupling are separated by a wavelength spacing of between approximately 0.1 nm and approximately 1.5 nm.
• the multimode VCSEL slave laser 20 can be biased to force multimode operation and to enhance modulation bandwidth. For example, it would not be unusual for the first order transverse modes to fall at a wavelength that is approximately 1 nm to approximately 2 nm shorter than the fundamental mode. In which case, the fundamental mode locking range could range from about 1.5 nm shorter to about 3 nm longer than the center wavelength of the fundamental mode.
• the laser source 100 should further comprise a polarization controller 30 because a biased multimode VCSEL slave laser will often emit fundamental and first-order transverse modes that comprise at least two different polarization modes.
• the polarization controller 30 can be used to match the respective polarizations of the single mode optical output 12 and the target mode of the multimode VCSEL slave laser 20.
• the single mode optical output 12 of the master laser 10 can be optically coupled to the optical resonator 22 of the multimode VCSEL slave laser 20 through an optical circulator 40 to prevent optical feedback to the master laser 10.
• the single mode optical output 12 of the master laser 10 can be optically coupled to optical resonators of an array of multimode VCSEL slave lasers via, for example, a 3 dB optical splitter, a beam splitter, or a polarizing beam displacer.
• the single mode optical output 12 of the master laser 10 can be optically coupled to the optical resonator of the multimode VCSEL slave laser through a coupling fiber that is mode matched with a fundamental or higher order transverse optical mode of the multimode VCSEL slave laser.

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• 2009
  • 2009-05-04 EP EP09739259A patent/EP2297826A1/de not_active Withdrawn
  • 2009-05-04 WO PCT/US2009/002742 patent/WO2009134456A1/en active Application Filing
  • 2009-05-04 KR KR1020107027040A patent/KR20110014171A/ko not_active Application Discontinuation
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