EP2297826A1 - Spectrally and spatially mismatched seeding of a multimode vcsel for modulation bandwidth enhancement - Google Patents

Spectrally and spatially mismatched seeding of a multimode vcsel for modulation bandwidth enhancement

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Publication number
EP2297826A1
EP2297826A1 EP09739259A EP09739259A EP2297826A1 EP 2297826 A1 EP2297826 A1 EP 2297826A1 EP 09739259 A EP09739259 A EP 09739259A EP 09739259 A EP09739259 A EP 09739259A EP 2297826 A1 EP2297826 A1 EP 2297826A1
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EP
European Patent Office
Prior art keywords
laser
mode
multimode
master
laser source
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP09739259A
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German (de)
French (fr)
Inventor
Connie Chang-Hasnain
Devang Parekh
Luis A Zenteno
Xiaoxue Zhao
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Corning Inc
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Corning Inc
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Publication date
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Publication of EP2297826A1 publication Critical patent/EP2297826A1/en
Withdrawn legal-status Critical Current

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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.

Abstract

A method of operating a laser source comprising a single mode master laser (10) and a multimode VCSEL slave laser (20) is provided. According to the method, the spatial and spectral coupling of the single mode optical output of the master laser and a targed 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. Further, a laser source is provided comprising a single mode master laser and a multimode VCSEL slave laser. The single mode master laser comprises a wavelength tuning element (60) and a spatial tuning element (15) that facilitate optically injected mode locking in the laser source spectrally mismatched optical seeding results in an enhanced modulation bandwidth of the VCSEL slave laser.

Description

SPECTRALLY AND SPATIALLY MISMATCHED SEEDING OF A MULTIMODE VCSEL FOR
MODULATION BANDWIDTH ENHANCEMENT
This applications claims the benefit of and priority to United States Patent application number 61/049,868, filed May 2, 2008.
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. 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.
According to the present disclosure, significantly enhanced bandwidth and transmission distance can be achieved using optical injection locking (OIL) as a technique to improve the direct modulation performance of multimode VCSELs. As a result, 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). For example, 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. Moreover, 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. It is contemplated that 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.
According to one embodiment of the present disclosure, a method of operating a laser source comprising a single mode master laser and a multimode VCSEL slave laser is provided. According to the method, 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. For the purposes of describing and defining the present invention, it is also noted that the present inventors have recognized that multimode VCSELs typically emit multiple transverse modes, which are at different wavelengths and have different spatial power distributions. At any given bias current or modulation conditions, these modes can exist simultaneously. Using the injection locking techniques described herein, 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.
According to another embodiment of the present disclosure, a laser source is provided 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. The following detailed description of specific embodiments of the present disclosure can be best understood when read in conjunction with the following drawings, where like structure is indicated with like reference numerals and in which:
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; and
Fig. 2 is a schematic illustration of a laser source comprising a single mode master laser and a multimode VCSEL slave laser
As is illustrated in Figs. 1 and 2, laser sources 100 according to the present disclosure comprise a single mode master laser 10 and a multimode VCSEL slave laser 20. In operation, 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 PMASTER/PSLAVE that is sufficient to stably injection lock the optical resonator 22 and generate a secondary output beam 25. According to the optical injection locking (OIL) techniques described herein, 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. For example, and not by way of limitation, 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. Alternatively, 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. For example, and not by way of limitation, a lensed or cleaved optical fiber can be utilized to restrict the cross section of the optical output 12 to less than about 'Λ of the cross section of the input aperture of the multimode optical resonator 22. In many embodiments, the cross section of the optical output of the master laser will be between approximately 2 μm and approximately 10 μm and the cross section of the input aperture of the multimode optical resonator will be between approximately 7 μm and approximately 50 μm.
The aforementioned progression in spectral coupling can be illustrated with reference to Table 1. Table 1 presents data that illustrates progression from a relatively mode-matched spectral coupling to a relatively mismatched spectral coupling. Specifically, under mode-matched spatial coupling the single mode optical output 12 of the master laser 10 starts with a center wavelength λMASTER that is greater than or relatively close to the fundamental transverse mode center wavelength λsuwε of the multimode VCSEL slave laser, e.g., λMASTER-λsLAvε = 0.48 nm. The single mode optical output 12 subsequently progresses to a relatively mismatched spectral coupling, where the single mode optical output 12 of the master laser 10 comprises a center wavelength λMASTER that is significantly less than the fundamental transverse mode center wavelength λsLAVE of the multimode VCSEL slave laser, e.g., λMASTER-λsLAvε = -0.366 nm. 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:
For the purposes of describing and defining the present invention, it is noted that the injection ratio PMASTER/PSLAVE is measured as a ratio of optical power estimated to be incident on the VCSEL versus the output power of the free running VCSEL. Also, it is noted that the value λMASTER-λsLAVE is measured as the wavelength difference of the master laser and the free running VCSEL.
It is noted that the spectral progression illustrated in Table 1 can be characterized as a progression from a relatively mode-matched state to a relatively mismatched state because, in progressing from λMASTER-λsLAVE = 0.48 nm to λMASTER-λSLAVE = -0.366 nm, the wavelength of the master laser will necessarily pass through λMASTER-λsLAVE = 0 nm, the ideal mode-matched spectral state, to λMASTER-λsuwε = -0.366 nm, a relatively mismatched spectral state. In executing the spectral progression of the present disclosure, it is noted that relatively mode-matched spectral states need not include the ideal mode- matched spectral state. Rather, 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.
The aforementioned spatial and spectral progressions for the case where the first order transverse modes illustrated in Fig. 1 is the target mode, would be analogous to those described above with respect to the fundamental transverse mode, with the exception that the mode-matched spectral and spatial states would be shifted to match the first order transverse mode, as is illustrated in the Table 2:
The data in 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.
By utilizing a power controller 50, a wavelength-tunable laser controller 60, and an output beam positioner 70 to optimize the injection power ratio and the progression of the spatial and spectral states towards a mismatched 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. For example, the injection ratio PMASTER/PSLAVE 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 PMASTER/PSLAVE 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.
The significant improvements in resonance frequency over a range of spectral coupling conditions show that a variety of spectral coupling conditions could be viewed as a suitable condition for the aforementioned relatively mismatched spatial coupling. To avoid performance degradation, it is desirable to have the laser resonance frequency greatly exceed the highest RF frequency of use. Spectral coupling can be controlled by providing a master laser that is a wavelength tunable laser and by tuning the center wavelength λMASTER 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. As is evident from the data presented in Tables 1 and 2, the center wavelength λMASTER can initially be greater than or less than the target mode center wavelength λsLAvε of the multimode VCSEL slave laser as it progresses towards the aforementioned mismatched spectral coupling. In many cases, it is contemplated that 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. For example, it is contemplated that 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. In some cases, it may merely be sufficient to ensure that the spectral coupling of the single mode optical output 12 is controlled such that the center wavelength XMASTER falls between the fundamental mode and a first order transverse mode of the slave resonator 22.
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.
Although not required, 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. Further, 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. It is also contemplated that 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. Finally, it is contemplated that 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.
It is noted that recitations herein of a component of the present disclosure being "configured" in a particular way, to embody a particular property, or to function in a particular manner, are structural recitations, as opposed to recitations of intended use. More specifically, the references herein to the manner in which a component is "configured" denotes an existing physical condition of the component and, as such, is to be taken as a definite recitation of the structural characteristics of the component. For the purposes of describing and defining the present invention it is noted that the term "substantially" is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term "substantially" is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.
It is noted that terms like "preferably," "commonly," and "typically," when utilized herein, are not utilized to limit the scope of the claimed invention or to imply that certain features are critical, essential, or even important to the structure or function of the claimed invention. Rather, these terms are merely intended to identify particular aspects of an embodiment of the present disclosure or to emphasize alternative or additional features that may or may not be utilized in a particular embodiment of the present disclosure.
For the purposes of describing and defining the present invention it is noted that the term "approximately" is utilized herein to represent the inherent degree of uncertainty that may be attributed to any quantitative comparison, value, measurement, or other representation. The term "approximately" is also utilized herein to represent the degree by which a quantitative representation may vary from a stated reference without resulting in a change in the basic function of the subject matter at issue.
Having described the subject matter of the present disclosure in detail and by reference to specific embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects. It is noted that one or more of the following claims utilize the term "wherein" as a transitional phrase. For the purposes of defining the present invention, it is noted that this term is introduced in the claims as an open-ended transitional phrase.

Claims

1. A method of operating a laser source comprising a single mode master laser and a multimode VCSEL slave laser, wherein: a single mode optical output of the master laser is spatially and spectrally coupled to an optical resonator of the multimode VCSEL slave laser at an injection ratio PMASTER/PSLAVE sufficient to optically injection lock the optical resonator of the multi- mode VCSEL slave laser; the method comprises controlling 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 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; the single mode optical output of the master laser, under the relatively mismatched spatial coupling, is primarily coupled to a peripheral spatial portion of the target mode of the multimode optical resonator; and the single mode optical output of the master laser, under the relatively mismatched spectral coupling, comprises a center wavelength that is less than the target mode center wavelength XSLAVE of the multimode VCSEL slave laser.
2. A method of operating a laser source as claimed in claim 1 wherein the spatial coupling is controlled by adjusting a beam spot position of the single mode optical output relative to an input aperture of the multimode optical resonator.
3. A method of operating a laser source as claimed in claim 2 wherein the beam spot position is adjusted by translating the optical output of the master laser along a dimension approximately parallel to the input aperture of the multimode optical resonator or by altering an angle of incidence of the optical output of the master laser relative to the input aperture of the multimode optical resonator.
4. A method of operating a laser source as claimed in claim 1 wherein the spatial coupling is facilitated by providing the single mode optical output of the master laser with an optical element that is configured to restrict a cross section of the optical output of the master laser at an input aperture of the multimode optical resonator to a fraction of the cross section of the input aperture.
5. A method of operating a laser source as claimed in claim 4 wherein the optical element comprises a lensed or cleaved optical fiber.
6. A method of operating a laser source as claimed in claim 4 wherein the cross section of the optical output of the master laser is less than about 1A of the cross section of the input aperture of the multimode optical resonator.
7. A method of operating a laser source as claimed in claim 4 wherein the cross section of the optical output of the master laser is between approximately 2 μm and approximately 10 μm and the cross section of the input aperture of the multimode optical resonator is between approximately 7 μm and approximately 50 μm.
8. A method of operating a laser source as claimed in claim 1 wherein: the multimode optical resonator defines a fundamental mode and a first order transverse mode; and the spectral coupling of the single mode optical output of the master laser is controlled such that the relatively mode-matched spectral coupling and the relatively mismatched spectral coupling are separated by a wavelength spacing that is a fraction of a mode spacing between the fundamental mode and the first order transverse mode of the multimode optical resonator.
9. A method of operating a laser source as claimed in claim 1 wherein: the multimode optical resonator defines a fundamental mode and a first order transverse mode; and the spectral coupling of the single mode optical output of the master laser is controlled such that the center wavelength λMASTER falls between the fundamental mode and a first order transverse mode.
10. A method of operating a laser source as claimed in claim 1 wherein: the multimode VCSEL slave laser is biased to force multimode operation and enhance modulation bandwidth; and the biased multimode VCSEL slave laser emits a fundamental mode and first-order transverse modes comprising at least two different polarization modes.
11. A method of operating a laser source as claimed in claim 10 wherein: the first order transverse modes are at a wavelength that is approximately 1 nm to approximately 2 nm shorter than the fundamental mode.
12. A method of operating a laser source as claimed in claim 1 wherein the spectral coupling of the single mode optical output of the master laser is 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.
13. A method of operating a laser source as claimed in claim 1 wherein the master laser comprises a wavelength tunable laser and the spectral coupling is controlled by tuning the center wavelength XMASTER of the single mode optical output of the master laser.
14. A method of operating a laser source as claimed in claim 1 wherein the spectral coupling is facilitated by tuning the center wavelength λMASTER by a fraction of a nanometer.
15. A method of operating a laser source as claimed in claim 1 wherein the single mode optical output of the master laser, under the relatively mode-matched spectral coupling, comprises a center wavelength λMASTER that is greater than or less than the target mode center wavelength λsLAVE of the multimode VCSEL slave laser.
16. A method of operating a laser source as claimed in claim 1 wherein the injection ratio PMASTER/PSLAVE is between approximately -5 dB and approximately 30 dB.
17. A method of operating a laser source as claimed in claim 1 wherein the single mode optical output of the master laser is coupled to the multimode VCSEL slave laser by utilizing a polarization controller to match the respective polarizations of the single mode optical output and the target mode of the multimode VCSEL slave laser.
18. A method of operating a laser source as claimed in claim 1 wherein the injection ratio PMASTER/PSLAVE and the spatial and spectral coupling are controlled to achieve a resonance frequency exceeding approximately 30 GHz.
19. A method of operating a laser source as claimed in claim 1 wherein the injection ratio PMASTER/PSLAVE and the spatial and spectral coupling are controlled to achieve a resonance frequency exceeding approximately 50 GHz and a 3 dB bandwidth exceeding approximately 30 GHz.
20. A laser source comprising a single mode master laser and a multimode VCSEL slave laser, wherein: the single mode optical output of the master laser is spatially and spectrally coupled to an optical resonator of the multimode VCSEL slave laser at an injection ratio PMASTER/PSLAVE sufficient to stably injection lock the optical resonator of the multi-mode VCSEL slave laser; the single mode master laser comprises a wavelength tuning element that is configured to control the 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 in response to a wavelength tuning signal such that the laser source can progress between a relatively mode-matched spectral coupling to a relatively mismatched spectral coupling to facilitate optically injected mode locking in the laser source; and the single mode master laser comprises a spatial tuning element that is configured to control the spatial coupling of the single mode optical output of the master laser and the target mode of the multimode optical resonator of the VCSEL slave laser in response to a spatial tuning signal such that the laser source can progress between a relatively mode- matched spatial coupling to a relatively mismatched spatial coupling to further facilitate optically injected mode locking in the laser source.
21. A laser source as claimed in claim 20 wherein the laser source further comprises a polarization controller that is configured to match the respective polarizations of the single mode optical output of the maser laser and a target mode of the multimode VCSEL slave laser.
22. A laser source as claimed in claim 20 wherein the laser source further comprises a power controller configured to adjust the injection ratio PMASTER/PSLAVE to achieve a laser source resonance frequency exceeding approximately 30 GHz.
EP09739259A 2008-05-02 2009-05-04 Spectrally and spatially mismatched seeding of a multimode vcsel for modulation bandwidth enhancement Withdrawn EP2297826A1 (en)

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US10707650B2 (en) 2016-03-04 2020-07-07 Princeton Optronics, Inc. High-speed VCSEL device

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ES2430488B2 (en) * 2012-04-18 2014-04-24 Universidad De Cantabria Optical signal generation system
WO2014065332A1 (en) * 2012-10-26 2014-05-01 大学共同利用機関法人情報・システム研究機構 Light-emitting device and light emission method
US11588298B2 (en) 2020-06-23 2023-02-21 Hewlett Packard Enterprise Development Lp Coupled-cavity VCSELs for enhanced modulation bandwidth

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US10707650B2 (en) 2016-03-04 2020-07-07 Princeton Optronics, Inc. High-speed VCSEL device

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