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
  • H01S5/02—Structural details or components not essential to laser action
  • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
• • 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
  • H01S5/02—Structural details or components not essential to laser action
  • H01S5/026—Monolithically integrated components, e.g. waveguides, monitoring photo-detectors, drivers
  • H01S5/0265—Intensity modulators
• • 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
  • H01S5/1028—Coupling to elements in the cavity, e.g. coupling to waveguides adjacent the active region, e.g. forward coupled [DFC] structures
  • H01S5/1032—Coupling to elements comprising an optical axis that is not aligned with the optical axis of the active region
• • 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
  • H01S5/1053—Comprising an active region having a varying composition or cross-section in a specific direction
  • H01S5/1064—Comprising an active region having a varying composition or cross-section in a specific direction varying width along the optical axis
• • 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
  • H01S5/12—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 the resonator having a periodic structure, e.g. in distributed feedback [DFB] lasers
  • H01S5/125—Distributed Bragg reflector [DBR] lasers

Definitions

• the present invention relates generally to the field of optical communications devices, and more particularly to lasers.
• Photonic integrated circuits provide an integrated technology platform increasingly used to form complex optical circuits.
• PIC technology allows multiple optical devices, both active and passive, to be integrated on a single substrate.
• PICs may comprise integrated lasers, integrated receivers, waveguides, detectors, semiconductor optical amplifiers (SOA), gratings, and other active and passive semiconductor optical devices.
• SOA semiconductor optical amplifiers
• gratings and other active and passive semiconductor optical devices.
• Monolithic integration of active and passive devices in PICs provides an effective integrated technology platform for use in optical communications.
• a particularly versatile PIC platform technology is the integrated twin
• TG waveguide
• Twin waveguide combines active and passive waveguides in a
• TG provides a platform technology by which a variety of PICs, each with different layouts and components, can be fabricated
• Integrated components are defined by post-growth patterning
• components in a TG-based PIC can be separately optimized, with post-growth processing steps used to determine the location and type of devices on the PIC.
• optical modes For PIC devices such as lasers, the interaction between optical modes
• ATG asymmetric twin waveguide
• ATG structure significantly reduces modal interference by confining different modes of
• the asymmetric waveguides may be laterally tapered to reduce coupling losses by resonant or adiabatic coupling of the optical energy between the first and second
• the asymmetric waveguide design significantly reduces the interaction
• Applicants disclose a photo-detector device based on the asymmetric waveguide design.
• the asymmetric waveguide photodetectors are highly responsive and
• EMLs electroabsorption-modulated lasers
• the laser may be, for example, a distributed- feedback (DFB) or a distributed
• DBR Bragg-reflector
• EA electroabsorption
• the active regions of the laser and modulator typically include
• the present invention meets these and other needs in the art.
• the laser device waveguide based electroabsorption-modulated laser device.
• first waveguide having a gain region, such as a multi-quantum well region, for amplifying primarily a first mode of light
• second waveguide having a modulator
• the first waveguide is positioned vertically on top of the second waveguide and has a
• the first mode of light is
• the light encounters the modulator, which
• modulated laser device comprising more than two vertically integrated asymmetric
• the laser device comprises a first waveguide having a gain
• a region such as a multi-quantum well region, for amplifying primarily a first mode of light
• a second waveguide having a distributed Bragg reflector therein and for guiding primarily
• the first waveguide is positioned vertically on
• top of the second waveguide and the second waveguide is positioned vertically on top of
• the first waveguide has a lateral taper formed therein for transferring
• the first mode of light is amplified in the first waveguide and
• the light propagates in the second waveguide as the second mode of light and is transferred into the third waveguide
• an electroabsorption modulated laser device employing a distributed feedback (DFB) laser.
• the DFB modulated laser device comprises a first waveguide and a second waveguide.
• the first waveguide has a gain region and a grating therein to form a DFB laser.
• a signal out of the DFB laser is transferred via a lateral taper into the second waveguide wherein the signal is modulated.
• Light propagating in the first waveguide has a different effective index of refraction than the mode of light propagating in the second waveguide.
• Modulated lasers in accordance with the invention provide efficient optical coupling between the laser and modulator as well as effective electrical isolation between the laser and modulator devices. Furthermore, modulated lasers in accordance with the invention can be manufactured through a process that requires only a single epitaxial growth step. Post-growth processing steps determine the location of the laser and modulator. This simplifies the manufacturing process and allows for a high yield, relatively low cost integration method. Additional aspects of the invention are described in detail below.
• Figure 1 is a perspective view of an asymmetric twin waveguide electroabsorption modulated laser in accordance with an aspect of the invention
• Figure 2 is a perspective view of a portion of an asymmetric twin waveguide electroabsorption modulated laser in accordance with an aspect of the invention
• Figure 3 is a sectional view of an asymmetric twin waveguide
• Figure 4 is a sectional view of an alternative embodiment of an asymmetric
• twin waveguide electroabso ⁇ tion modulated laser in accordance with an aspect of the
• Figure 5 A is a flowchart of a process for manufacturing an asymmetric twin
• Figure 5B is a flowchart of a process for manufacturing an alternative
• Figure 6 provides a graph of the intensity of photoluminscence spectra
• Figure 7 A provides a graph of the output power through a modulator versus current for an asymmetric twin waveguide electroabso ⁇ tion modulated laser device in
• Figure 7B is a graph of output power extinction ratio versus applied
• Figure 8 is a perspective view of a portion of an asymmetric waveguide
• Figure 9 is a sectional view of an asymmetric waveguide electroabso ⁇ tion modulated laser in accordance with the invention.
• Figure 10 is a flowchart of a process for manufacturing an asymmetric waveguide electroabso ⁇ tion modulated laser in accordance with an aspect of the
• Figure 11 is a perspective view of a portion of an asymmetric twin
• Figure 12A is a sectional view of an asymmetric twin waveguide
• Figure 12B is a sectional view of an alternative embodiment of an
• the present application is directed toward monolithically
• An asymmetric twin waveguide (ATG)
• the ATG design employs two waveguides wherein each waveguide is designed to guide primarily one mode of light with each mode having a different effective index of refraction.
• a lateral taper in one of the waveguides induces coupling of light between the waveguides.
• the lateral taper operates to change the effective refractive index of a mode of light traveling in the first waveguide to a second mode that propagates primarily in the second waveguide. This transition occurs over the length of the taper.
• a mode of light having a first index of refraction may begin to propagate in second waveguide at the beginning of a taper, and be transitioned to a second mode of light having a lower effective index of refraction by the end of the taper region which causes the mode to be essentially locked into propagating in the second waveguide.
• the present application is directed toward laser PIC devices having a plurality of vertically integrated asymmetric waveguides with lateral tapers formed therein.
• an electroabso ⁇ tion modulated laser device is provided having a twin asymmetric waveguide design. Light is amplified across the length of a first waveguide and coupled into a second waveguide via a lateral taper. A modulator operates to modulate the light propagating in the second waveguide.
• light that is generated and amplified in the first asymmetric waveguide is modulated by a modulator in the second asymmetric waveguide.
• FIG 1 provides a perspective view of an exemplary asymmetric twin waveguide electroabso ⁇ tion modulated laser in accordance with an aspect of the present invention.
• electroabso ⁇ tion modulated laser device 110 comprises a laser
• a signal generated by laser region 104 is
• modulated by modulator 106 is modulated by modulator 106.
• device 110 comprises first waveguide 114 and second
• waveguide 116 situated on substrate 112.
• waveguide 114 has a gain region formed therein for amplifying light propagating in the waveguide.
• the light propagating in waveguide 114 is transferred into waveguide 116 via lateral tapers 122 formed in waveguide 114.
• Waveguide 116 has grating sections 128 formed therein. Grating sections 128 operate with the gain section in waveguide 114 to form a distributed Bragg reflector (DBR) laser.
• DBR distributed Bragg reflector
• laser region 104 comprises waveguide 114 and the portion of waveguide 116 between gratings 128.
• the light emitted by the DBR laser region 104 enters modulator region 106 of waveguide 116.
• Modulator region 106 operates to modulate the signal out of the laser.
• Figure 2 provides a perspective view of a portion of an exemplary asymmetric twin waveguide electroabso ⁇ tion modulated laser in accordance with an aspect of the present invention.
• the monolithically integrated twin waveguide modulated laser device 110 is situated on substrate 112 and comprises a first waveguide 114 and a second waveguide 116.
• Waveguide 114 has multi-quantum well area 118 formed therein for amplifying light propagating in waveguide 114.
• quantum well area 118 comprises five quantum wells.
• Laser electrical contact area 120 is used to apply a voltage across multi-quantum well area 118 and thereby generate a lasing signal.
• the materials and relative thickness of those materials comprising waveguide 114 have been selected such that a single mode of light propagates primarily in waveguide 114.
• the single mode of light has an effective index of refraction of about 3.24.
• Waveguide 114 has lateral tapers 122 formed therein for transferring light into waveguide 116.
• the width of the tapered end of waveguide 116 referred to herein as W TAPEND , is 1 ⁇ m.
• the width of the taper at one point, which in the exemplary embodiment is the taper's widest point, refe ⁇ ed to herein as W TAP is between about 1.8 and 2.2 ⁇ m.
• the length of the taper from its end to the point corresponding to W TAP which is referred to herein as L TAP , is between about 100 and 1250 ⁇ m.
• the above described values for WTA P END, W T AP, and L T AP result in a lateral taper angle, ⁇ , of between about 0.09 and 0.23 degrees.
• Waveguide 116 is located below waveguide 114 and is integrally formed
• Waveguide 116 has been designed to guide primarily one mode of light
• the mode of light has a lower effective index of refraction than the mode of light propagating in waveguide 114.
• refraction of the mode of light propagating in waveguide 116 is between about 3.2 and
• Waveguide 116 comprises multi-quantum well region 124, which, in one
• embodiment comprises ten quantum wells. Electrical contact 126 is used to induce a
• the reverse bias results in the modulation of the signal being output from waveguide 126.
• multi-quantum well region 124 is transparent to the laser
• DBR Bragg reflector
• electroabso ⁇ tion modulated lasers is having effective electrical isolation between the laser
• Figure 3 provides a sectional view of the asymmetric twin waveguide laser shown in
• waveguide 114 comprises a p doped area 210, multi-quantum well
• Waveguide 116 is situated on top of n+ doped substrate 112 and comprises quantum well region 124, and n+ doped region 214.
• N doped region 214 is situated adjacent to n doped region 212 of waveguide 114.
• a portion of top cladding layer 214 of waveguide 116 located under contact 126 is converted locally to a p type region 220 using acceptor diffusion. The diffusion
• quantum well region 124 At the junction of region 220 and cladding 214 a reverse biased
• p-n junction is formed that provides electric isolation between the modulator and the laser.
• composition of the waveguides operates to provide electrical isolation between
• the laser and modulator are the laser and modulator.
• asymmetric twin waveguide laser is depicted in Figure 4. As shown, waveguide 114
• Waveguide 116 is situated on top of substrate 112 and below waveguide 114.
• Waveguide 116 comprises n doped cladding layer 314, quantum well region 124, and highly n+ doped
• Reverse bias for the modulator is applied between n+ contact layer 316 and substrate
• ion implantation region 320 is formed in n+ layer 312, contact layer 316, and
• the ion implantation region creates a resistance of several hundred kilo-
• a great advantage of asymmetric waveguide technology is that it lends itself to the creation of devices using a single growth step.
• the MQW region 124 is grown.
• the MQW region 124 comprises ten InGaAsP quantum wells
• (SCH) layers which are each about 0.05 ⁇ m thick.
• the modulator is followed by a 0.35
• the laser MQW region 118 is grown on top of this.
• MQW region 118 comprises five InGaAsP quantum wells with an emission wavelength of
• a 0.1 ⁇ m InP layer is grown, followed by a 0.02 ⁇ m InGaAsP etch stop, and a 1
• bandgap wavelength ⁇ g 1.2 ⁇ m
• Figure 5 A is a flowchart of a process for manufacturing an asymmetric twin
• step 410 a first step of masking and etching steps. As shown, at step 410, a first step of masking and etching steps.
• MBE molecular beam epitaxy
• MOCVD metal-organic chemical vapor deposition
• the outline of waveguide 114 which has lateral taper 122 formed therein, is defined via masking, and the surrounding layers etched away to the top of waveguide 116.
• waveguide 116 is defined via masking and the su ⁇ ounding areas etched away to the top of substrate 112.
• the grating 128 is formed in waveguide 116 via an interferometric method or e-beam lithography.
• p+ region 220 is formed in waveguide 116 using acceptor impurity diffusion techniques.
• contacts 120 and 126 are formed on waveguide 114 and waveguide 116 respectively.
• FIG. 5B is a flowchart of a process for manufacturing an asymmetric twin waveguide electroabso ⁇ tion modulated laser as depicted in Figure 4.
• a monolithic structure comprising layers as described above is grown by MBE or
• the outline of waveguide 114 which has lateral taper 122 formed therein, is defined via masking, and the surrounding layers etched away to the top of waveguide 116.
• waveguide 116 is defined via masking and the surrounding areas etched away to the top of substrate 112.
• the grating 128 is formed in waveguide 116 via an inteferometric method or e-beam lithography.
• electrical isolation region 320 is formed in waveguide 116 using standard ion implantation techniques.
• contacts 120 and 126 are formed on waveguide 114 and waveguide 116 respectively.
• Figure 6 provides a graph of the intensity of photoluminscence spectra versus photoluminescence wavelength for each of the laser, represented by line 512, and the modulator, which is represented by line 510, of the device depicted in Figure 4. As shown, there is a shift of 33nm in the photoluminescence wavelength between the laser and modulator. The actual lasing wavelength is 1540 nm which is detuned by 52 nm from the modulator photoluminescence peak.
• Figures 7 A and 7B are graphs of the output from an asymmetric twin waveguide electroabso ⁇ tion modulated laser device such as shown in Figure 4.
• 7A provides a graph of the output power through the modulator versus laser drive current.
• Figure 7B is a graph of output power extinction ratio versus applied modulator voltage.
• the thickness of the cladding layer should be relatively large
• micrometer leads to a rapid increase in the waveguide loss in the modulator section.
• region 104 present conflicting design considerations - the modulator operates best when
• an electroabso ⁇ tion modulated laser device having more than two asymmetric waveguides. Light is amplified across the length of a
• first waveguide and coupled into a second waveguide via a lateral taper.
• second waveguide The second
• waveguide comprises a distributed Bragg reflector to ensure stability of power
• a modulator in the third waveguide operates to
• Figure 8 provides a perspective view of an exemplary electroabso ⁇ tion
• modulated laser device 710 comprising more than two asymmetric waveguides.
• device 710 comprises laser waveguide 712, passive waveguide 714, and
• modulator waveguide 716 all of which are situated on substrate 718.
• Waveguide 712 has lateral
• tapers 722 formed therein for moving light between waveguide 712 and waveguide 714.
• waveguide 714 has lateral tapers 724 formed therein for moving light between
• waveguide 714 and waveguide 716 are waveguide 714 and waveguide 716.
• Waveguide 712 comprises multi-quantum well area 730 for amplifying
• Laser electrical contact area 732 is used to apply a voltage across multi-quantum well area 730 for pu ⁇ oses of amplifying the signal in the waveguide.
• the materials comprising waveguide 712 have been selected such that a single mode of light propagates primarily in waveguide 712.
• the single mode of light has an effective index of refraction of about 3.26.
• Lateral taper 722 operates to guide
• taper 722 is
• Waveguide 714 is located below waveguide 712 and is integrally formed
• Waveguide 714 comprises passive propagating area 733 for moving light
• Grating sections 714 forms a
• Lateral taper 724 operates to transfer the light propagating in waveguide
• Waveguide 714 is made from a high optical quality material with
• taper 724 is relatively long, for example, in the range between about
• the high quality, low optical loss material and long taper 250 and 600 micrometers.
• Waveguide 714 is
• waveguide 714 is between about 3.23 and 3.24.
• Waveguide 716 is located vertically below waveguide 714 and is integrally
• Waveguide 716 comprises multi-quantum well region 736 and has
• Contact 740 is used to induce a reverse bias across
• quantum well region 736 so as to induce bandgap shift and abso ⁇ tion of the signal propagating in the waveguide.
• the reverse bias provides the capability to modulate the
• Waveguide 716 is designed to guide primarily
• the mode of light has a lower effective index of refraction than the mode of light propagating in waveguide 714.
• the mode of light has a lower effective index of refraction than the mode of light propagating in waveguide 714.
• effective index of refraction of the mode of light propagating in waveguide 716 is between about 3.2 and 3.21.
• Figure 9 provides a sectional view of the modulated laser device 710.
• waveguide 712 comprises p doped cladding layer
• Waveguide 714 comprises
• n doped region 746 passive waveguide region 733, and n doped region 748.
• n doped region 750 and multi-quantum well region 736.
• n cladding layer 750 is created in n cladding layer 750 and operates similarly to that described above with
• the cladding thickness is about 0.5 micrometers, which allows for the use of
• a taper 722 of between about 100 and 120 micrometers.
• waveguide 714 is made from a high optical quality material with no
• the relative thinness of the cladding layers provides for a relatively shallow grating in order to form Bragg grating 734.
• the thickness of the modulator portion of the device With respect to the modulator portion of the device, the thickness of the modulator portion of the device, the thickness of
• cladding layers 748 and 750 at the junction of waveguides 714 and 716 can be maximized
• the increased thickness of the cladding minimizes the interference by contact 740 with signals propagating in waveguide 716.
• a 0.5 ⁇ m thick InP buffer layer is grown on a (100) p-doped InP substrate 718.
• the modulator MQW region 736 is grown.
• the modulator MQW region 736 comprises ten
• InGaAsP quantum wells with an emission wavelength of about ⁇ 1.50 ⁇ m, separated by
• SCH confinement heterostructure
• modulator waveguide 716 is followed by a 1 ⁇ m thick InP layer that separates it from
• Passive waveguide 714 is grown next, and comprises a 0.5 ⁇ m
• InP layer a 0.05 ⁇ m thick, n+ doped InGaAsP layer, and another 0.22 ⁇ m thick InP
• Laser MQW waveguide 712 is grown on top of this. Laser waveguide 712
• FIG 10 is a flowchart of a process for manufacturing an asymmetric twin waveguide electroabso ⁇ tion modulated laser as depicted in Figures 8 and 9.
• the modulated laser is manufactured through a series of masking and etching steps. As shown,
• a monolithic structure comprising layers as described above is grown by MBE
• waveguide 714 which has lateral taper 724 formed therein, is defined via masking
• outline of waveguide 716 is defined via masking, and the surrounding layers etched away
• grating reflector 734 is formed in waveguide 714
• p+ region 752 is
• contacts 120 and 126 are formed on waveguide 712 and waveguide 714 respectively.
• FIG. 11 provides a perspective view of an electroabso ⁇ tion modulated laser device in accordance with the
• the device of Figure 11 comprises a first
• Waveguide 1110 and a second waveguide 1112.
• Waveguide 1110 comprises a gain region
• Waveguide 1112 comprises a gain region
• a signal out of the DFB laser is transfe ⁇ ed via lateral taper 1124 into waveguide 1114 where the signal is modulated.
• the DFB laser is transfe ⁇ ed via lateral taper 1124 into waveguide 1114 where the signal is modulated.
• the laser portion of the device of Figure 11 is comprised
• top waveguide 1110 entirely in top waveguide 1110. Accordingly, there are no grating sections in second waveguide 1112.
• the device depicted in Figure 11 is consistent with the asymmetric designs designed above. Accordingly, the light propagating in waveguide 1110 has a different
• Figures 12A and 12B provide sectional views of two alternative
• isolation is provided between the laser region of the device and the modulator region of the device
• ion implant region 1210 which operates similarly to the embodiments described
• grating region 1118 is formed in the top waveguide.
• an asymmetric twin waveguide based electroabso ⁇ tion modulated laser PIC is
• the devices are
• the devices are relatively
• an asymmetric waveguide electroabso ⁇ tion modulate laser in accordance with the invention may comprise doping
• an asymmetric waveguide electroabso ⁇ tion modulated laser in accordance with the invention may be employed to make high sensitivity 40GHz transmitters for optical communication links. Accordingly, reference should be made to the appended claims as indicating the scope of the invention.

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• Physics & Mathematics (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Optics & Photonics (AREA)
• Semiconductor Lasers (AREA)
• Optical Integrated Circuits (AREA)
• Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)
• Lasers (AREA)

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