WO2021148121A1 - Laser dfb à section de guide d'onde centrale inclinée - Google Patents

Laser dfb à section de guide d'onde centrale inclinée Download PDF

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Publication number
WO2021148121A1
WO2021148121A1 PCT/EP2020/051579 EP2020051579W WO2021148121A1 WO 2021148121 A1 WO2021148121 A1 WO 2021148121A1 EP 2020051579 W EP2020051579 W EP 2020051579W WO 2021148121 A1 WO2021148121 A1 WO 2021148121A1
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WO
WIPO (PCT)
Prior art keywords
laser
waveguide
region
grating
central region
Prior art date
Application number
PCT/EP2020/051579
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English (en)
Inventor
Xin Chen
Original Assignee
Huawei Technologies Co., Ltd.
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Huawei Technologies Co., Ltd. filed Critical Huawei Technologies Co., Ltd.
Priority to CN202080091699.0A priority Critical patent/CN114902507A/zh
Priority to PCT/EP2020/051579 priority patent/WO2021148121A1/fr
Publication of WO2021148121A1 publication Critical patent/WO2021148121A1/fr

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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
    • H01S5/10—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
    • H01S5/124—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 incorporating phase shifts
    • H01S5/1243—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 incorporating phase shifts by other means than a jump in the grating period, e.g. bent waveguides
    • 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
    • H01S5/20—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers
    • H01S5/22—Structure or shape of the semiconductor body to guide the optical wave ; Confining structures perpendicular to the optical axis, e.g. index or gain guiding, stripe geometry, broad area lasers, gain tailoring, transverse or lateral reflectors, special cladding structures, MQW barrier reflection layers having a ridge or stripe structure

Definitions

  • This invention relates to lasers, for example to promoting single-mode lasing.
  • High-performance and low-cost laser modules are used in applications such as large-capacity and high-speed optical access networks.
  • a conventional laser diode generally comprises a semiconductor block which has a front face or facet, a rear face or facet opposite to the front facet and a laser cavity formed therebetween.
  • the cavity traditionally comprises an active layer interposed between layers of p- or n-type semiconductor material.
  • One or more coating layers such as anti-reflection (AR) or high- reflection (HR) coatings, may be applied to the front and the rear facets to provide a predetermined reflectivity.
  • a Bragg grating acts as the wavelength selective element for at least one of the faces and provides feedback, reflecting light back into the cavity to form the resonator.
  • a waveguide restricts the region in which light can propagate and comprises a region of increased refractive index relative to the surrounding material, such that total internal refection of light occurs within the waveguide. This makes it possible to direct the emitted light into a collimated beam, and allows a laser resonator to be built such that light can be coupled back into the gain medium.
  • InP single-mode DFB lasers are widely used in telecommunication systems. Due to symmetry, a conventional DFB with a full grating, as illustrated in the plan view of Figure 1, has two competing lasing modes.
  • the Bragg grating comprises a series of parallel elements, shown at 101.
  • a tapered waveguide can also be used to break the DFB structure symmetry.
  • tapering the waveguide affects the refractive index of the waveguide, such that the grating must be chirped to result in a single wavelength output.
  • a curved waveguide may be used to break the DFB structure symmetry.
  • Kappa*L > 2.0 has been frequently used (where Kappa is the grating strength and L is the length of the grating). Consequently, due to the longitudinal spatial-hole burning effect, mode-hop can occur, with bandwidth roll-off at low frequency.
  • an asymmetric corrugation-pitch-modulated (CPM) grating has been applied in a laser structure, as illustrated in Figure 2.
  • the period of the APCM grating section 201 is about 0.4 nm different to the standard pitch of the grating 202, which is around 200 nm. It has been demonstrated that asymmetric corrugation-pitch-modulated ACPM lasers have higher frequency response and enable direct modulation at 28 Gb/s with a high mask margin of 22% over 1000 waveforms at 55°C (OFC2013, Oth4H.3, 2013).
  • an e-beam is required to write the APCM grating along with the standard grating, which is difficult to control, and yield can be low.
  • a laser having a rear reflector, a front reflector and a laser cavity defined between the rear reflector and the front reflector, the cavity having a waveguide comprising a Bragg grating, the waveguide comprising a first outer region adjacent the rear reflector and a second outer region adjacent the front reflector and a central region between the first and second outer regions, the central region of the waveguide being axially offset relative to the first and second outer regions and the grating in the central region having a greater effective grating pitch than in the first and second outer regions.
  • Using a waveguide with an angled central section may improve yield, selectively promote a preferred lasing wavelength and reduce mode-hop.
  • the Bragg grating may extend across the first outer region, the central region and the second outer region of the waveguide.
  • the Bragg grating may comprise a series of elements that are parallel to each other in the first outer region, the central region and the second outer region of the waveguide.
  • the elements of the Bragg grating may have the same pitch perpendicular to themselves in the first outer region, the central region and the second outer region of the waveguide.
  • a constant physical grating pitch can therefore be applied along the waveguide structure. It is also easy to control the length of the grating in the central section. As a result, the DML yield may be very high and using this configuration may avoid the need for an expensive and complicated chirped grating.
  • a low-cost holographic grating process can be used to fabricate the uniformly pitched grating.
  • the elements of the Bragg grating in the first outer region and the second outer region may have same effective pitch as each other. This may simplify the manufacture of the laser.
  • the central region of the waveguide may act as an asymmetric corrugation pitch modulated grating.
  • a three-section waveguide DFB laser can therefore be used to realize a laser having similar properties to a single-mode ACPM DFB laser, but that is easier to fabricate.
  • Each region of the waveguide may promote light propagation along a respective axis and the axis of the central region may be angularly offset with respect to the axes of the first and second outer regions.
  • the axis of the central region may be angularly offset with respect to the axes of the first and second regions by between 1 to 10 degrees. This may allow the effective pitch of the waveguide regions to be selected accordingly and controlled depending on the application of the laser.
  • the axes of the first and second outer regions may be parallel. This may simplify the manufacture of the laser.
  • the effective pitch of the Bragg grating in the central region may be between 0.01 and 1 nm longer than that of the first and second outer regions.
  • the difference in the effective pitch may be chosen accordingly and may result in improved yield of the laser.
  • the waveguide may extend between the front and rear reflectors. This may allow the light to be reflected within the cavity, which may improve the yield of the laser.
  • the front reflector may be coated with an anti-reflection coating.
  • the rear reflector may be coated with an anti-reflection coating or a high-reflection coating. This may improve the performance of the laser.
  • the waveguide may be a ridge waveguide or a buried heterostructure waveguide. This may allow flexibility in manufacturing the laser.
  • the laser may be a distributed feedback laser. This may allow the laser to be used in applications such as telecommunications.
  • the waveguide may have a width between 0.5 pm to 3.0 pm. This may allow the effective refractive index of the waveguide to be selected accordingly.
  • the strength of the Bragg grating Kappa*L may be in the range from 0.7 to 3.0. This may allow the optical properties of the laser to be selected accordingly.
  • Figure 1 schematically illustrates a plan view of a conventional DFB laser
  • Figure 2 illustrates an example of a DFB laser with an ACPM grating
  • Figure 3 schematically illustrates a side view of an example of the DFB laser described herein;
  • Figure 4 schematically illustrates a cross-section through an example of the DFB laser described herein;
  • Figure 5 schematically illustrates a plan view of an example of the DFB laser described herein.
  • one form of DFB laser comprises a semiconductor block which has a front face 301 , a rear face 302 opposite to the front face and a laser cavity formed therebetween.
  • the one or both of the front and rear faces may be cleaved facets. It is preferable that the front and rear facets are aligned parallel to one another.
  • a high-reflection (HR) coating may be applied to the rear facet.
  • the rear facet acts as a rear reflector and the front facet can act as a front reflector.
  • a HR coating or an anti-reflection (AR) coating may be applied to the front face. Light exits the laser cavity at the front face, shown at 303.
  • the laser cavity comprises an active layer 304 interposed between layers of p- and n-type semiconductor material, shown at 305 and 306 respectively.
  • the semiconductor layers are made from InP.
  • other semiconductor materials such as GaAs, may be used.
  • the material forming the cavity may be selectively doped in the region of the p- and n-type layers 305, 306.
  • Layers 304, 305 and 306 are defined in a substrate 307. In this example, the layers are elongated in a direction extending between the rear reflector and the front reflector.
  • the waveguide 308 of the laser comprises a material with a refractive index n greater than that of the substrate. Light is emitted from the end of the waveguide at the front face of the laser.
  • the waveguide is a ridge waveguide.
  • a ridge waveguide may be created by etching parallel trenches in the material either side of the waveguide to create an isolated projecting strip, typically less than 10 pm wide and several hundred pm long.
  • a material with a lower refractive index than the waveguide material can be deposited at the sides of the ridge to guide injected current into the ridge.
  • the ridge may be surrounded by air on the three sides that are not in contact with the substrate beneath the waveguide.
  • the ridge may also be coated with gold to provide electrical contact and to assist heat removal from the ridge when it is producing light.
  • the waveguide comprises a Bragg grating 309.
  • the Bragg grating may be positioned between the waveguide ridge 308 and the p-lnP layer 305.
  • the Bragg grating can be positioned under the active region, i.e. in the n-doped layer 306.
  • the Bragg grating comprises a series of parallel elements 310 of regular physical spacing, A std , along a first axis F. Each of the elements extends orthogonally to the first axis.
  • the parallel elements extend across the width of the waveguide.
  • the width of the waveguide w is measured parallel to the elements.
  • the grating Kappa*L is preferably between 0.7 to 3.0.
  • the waveguide 308 comprises three regions: first and second outers regions Li and respectively, and a central region L ang .
  • the first and second outer waveguide regions and the central waveguide region are optically coupled to each other.
  • the first outer region is adjacent (or terminates at) the rear reflector 302 and the second outer region is adjacent (or terminates at) the front reflector 301.
  • the central region is between the first and second outer regions and is axially offset relative to the first and second outer regions.
  • Each region of the waveguide promotes light propagation along a respective axis: the first outer section promotes light propagation along axis Di, the central section L ang promotes light propagation along axis D2 and the second outer section l_2 promotes light propagation along axis D3.
  • the axis D2 of the central region is angularly offset with respect to the axes of the first and second outer regions, Di and D3 respectively by angle Q.
  • the axis of the central region is preferably angularly offset with respect to the axes of the first and second regions by between 1 to 10 degrees, depending on the waveguide and laser design.
  • the axes of the first and second outer regions are parallel with each other and straight (i.e. aligned with the length of the cavity, perpendicular to the width of the waveguide) and the axis of the central section L ang is offset at an angle Q relative to the axes of each of the first and second outer regions.
  • the Bragg grating 309 extends across all three regions of the waveguide and has a uniform physical pitch along the whole waveguide (i.e. a constant physical spacing) of A std along axis F.
  • the elements of the waveguide 310 are parallel to each other.
  • the first outer waveguide section Li comprises a first subset of the elements 310
  • the second outer waveguide section l_2 comprises a second subset of the elements 310
  • the central waveguide section comprises a third subset of the elements 310.
  • the axis F is parallel to the directions Di and D3 and the axis F is orthogonal to both the front reflector 301 and the rear reflector 302.
  • the first and second outer waveguide sections and l_2 have a different effective pitch, A ef r, for light travelling along the waveguide from the rear face towards the front face than the central waveguide section L ang .
  • the first and second outer waveguide sections are straight, with grating pitch A std , which corresponds to a Bragg grating wavelength of A standard.
  • the uniformly pitched waveguide is tilted by an angle of Q relative to the first and second outer sections.
  • Angling the central waveguide section increases the path length of light travelling between the elements of the Bragg grating in the central section.
  • the physical pitch of the waveguide has a constant value of A std .
  • the elements of the Bragg grating are arranged across the width of the waveguide and the first and second outer waveguide sections are aligned with the length of the cavity (i.e. the first and second outer waveguide sections are straight).
  • the central waveguide section is angled relative to the length of the cavity.
  • the Bragg grating elements extend perpendicular to the length of the cavity.
  • the rear reflector is planar and the length of the cavity is measured in a direction perpendicular to the rear reflector (along axis F in Figure 5).
  • first and second outer regions have a physical grating pitch of 200 nm and the central region is angled at an angle Q of 4 degrees between the first and second outer waveguide regions, this results in an effective pitch of 200.49 nm in the central waveguide region.
  • the effective pitch of the Bragg grating in the central region is between 0.01 nm and 1 nm longer than that of the first and second outer regions.
  • the effective pitch of the Bragg grating in the central region is between 0.001-1% longer than that of the first and second outer regions, preferably between 0.005-0.5%, more preferably between 0.1 -0.3%.
  • the effective pitch of the Bragg grating in the central region is between 0.01 nm and 0.5% longer than that of the first and second outer regions.
  • the first and second outer regions of the waveguide are straight (i.e. the directions Di and D3 are parallel to the length of the cavity, which is along axis F in Figure 5) and the central region is angled relative to the two outer regions (and therefore angled relative to the length of the cavity and axis F).
  • one or both of the first and second outer regions may be angled relative to the axis perpendicular to the elements of the Bragg grating. Therefore, the Bragg grating in the first outer region may have a different effective pitch to the Bragg grating in the second outer region. In this case, the effective pitch of the grating in the central region is greater than the effective pitch of the Bragg grating in each of the first and second outer regions.
  • U may be between 5% to 60% of L.
  • L ang may be between 15% to 40% of L.
  • the waveguide for the DFB laser may be a buried heterostructure (BH) or a shallow ridge waveguide.
  • the waveguide width may be between approximately 0.5 pm to 3.0 pm.
  • the central waveguide section L ang may have the same waveguide width as the outer waveguide sections and l_2. Alternatively, the central waveguide section L ang may have a different waveguide width to the outer waveguide sections and l_2. Alternatively, all of the waveguide sections may have different widths to each other.
  • the semiconductor layers and the active region of the cavity may be made of InP, GaAs, or another semiconductor material.
  • a constant physical grating pitch A s td
  • a s td a constant physical grating pitch
  • the DML yield may be very high.
  • a three-section waveguide DFB laser can be used to realize a laser having similar properties to a single-mode ACPM DFB laser.
  • the laser described herein is easier to fabricate than an ACPM DFB laser, as there is no need to use an e-beam to write the grating, and no need to change the grating period along the waveguide.
  • the grating along the waveguide has the same pitch (the grating period is constant for the whole waveguide).
  • a low-cost holographic grating process can be used to fabricate the uniformly pitched grating.
  • the physical pitch of the grating may be, for example, approximately 300 nm, 200 nm, or 50 nm.
  • the Bragg grating may be an index coupled grating, a gain coupled grating or a complex coupled grating.
  • the layer comprising the waveguide and/or the grating may be fabricated from a p-doped or n-doped semiconductor material.
  • the proposed DFB laser breaks the structure symmetry of the laser cavity.
  • using a waveguide with an angled central section may selectively promote a preferred lasing wavelength and reduce mode-hop.
  • a HR or AR coating can be applied to the facets of the laser to enhance the output power and reduce the structure symmetry further.
  • the laser structure may be integrated with another optically functional structure, for example an electroabsorption modulator (EAM), a Mach-Zehnder modulator, or an amplifier.
  • EAM electroabsorption modulator
  • Mach-Zehnder modulator Mach-Zehnder modulator
  • amplifier amplifier
  • the front face of the laser may be optically coupled to a lens.

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  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Semiconductor Lasers (AREA)

Abstract

La présente invention concerne un laser à rétroaction répartie (DFB) ayant une facette arrière (302), une facette avant (301) et une cavité de laser définie entre la facette arrière et la facette avant. La cavité comporte un guide d'ondes (308) comprenant un réseau de Bragg. Le guide d'ondes comprend une première région externe (LI) adjacente à la facette arrière (302), une seconde région externe (L2) adjacente à la facette avant (301) et une région centrale entre les première et seconde régions externes. La région centrale du guide d'ondes est décalée axialement par rapport aux première et seconde régions externes et le réseau de la région centrale a un pas de réseau efficace supérieur à celui des première et seconde régions externes. Un seul mode d'émission laser peut être obtenu avec un pas de réseau constant.
PCT/EP2020/051579 2020-01-23 2020-01-23 Laser dfb à section de guide d'onde centrale inclinée WO2021148121A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
CN202080091699.0A CN114902507A (zh) 2020-01-23 2020-01-23 带有成角度的中心波导部分的dfb激光器
PCT/EP2020/051579 WO2021148121A1 (fr) 2020-01-23 2020-01-23 Laser dfb à section de guide d'onde centrale inclinée

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/EP2020/051579 WO2021148121A1 (fr) 2020-01-23 2020-01-23 Laser dfb à section de guide d'onde centrale inclinée

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WO2021148121A1 true WO2021148121A1 (fr) 2021-07-29

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2023227189A1 (fr) * 2022-05-23 2023-11-30 Huawei Technologies Co., Ltd. Laser à semi-conducteur incliné

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4833687A (en) * 1985-12-18 1989-05-23 Sony Corporation Distributed feedback semiconductor laser
WO2018197015A1 (fr) * 2017-04-28 2018-11-01 Huawei Technologies Co., Ltd. Laser à guide d'ondes incurvé

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4833687A (en) * 1985-12-18 1989-05-23 Sony Corporation Distributed feedback semiconductor laser
WO2018197015A1 (fr) * 2017-04-28 2018-11-01 Huawei Technologies Co., Ltd. Laser à guide d'ondes incurvé

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
SALZMAN J ET AL: "DISTRIBUTED FEEDBACK LASERS WITH AN S-BENT WAVEGUIDE FOR HIGH-POWER SINGLE-MODE OPERATION", IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, IEEE SERVICE CENTER, PISCATAWAY, NJ, US, vol. 1, no. 2, 1 June 1995 (1995-06-01), pages 346 - 355, XP000521096, ISSN: 1077-260X, DOI: 10.1109/2944.401214 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2023227189A1 (fr) * 2022-05-23 2023-11-30 Huawei Technologies Co., Ltd. Laser à semi-conducteur incliné

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CN114902507A (zh) 2022-08-12

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