Directly modulated laser

Abstract

The invention provides a directly modulated laser, which comprises a substrate, an epitaxial layer, a buffer layer, a grating layer, a lower limiting layer, an active layer, an upper limiting layer, a corrosion cut-off layer, a cladding and a contact layer, the structure of the grating layer is a convex grating structure with a lambda / 8 phase shift, the grating layer is located on the N-type doped side, and the convex grating structure with the lambda / 8 phase shift is used for reducing the photon density at the phase shift position through the negative reflector loss feedback effect and limiting hole gathering on the P-type doped side through the characteristic that the electron mobility is larger than the hole mobility.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically to a direct-modulation laser. Background Technology

[0002] Direct-modulated lasers have been widely used in fields such as fiber optic communication and data centers due to their small size and low power consumption.

[0003] Existing λ / 4 phase-shift grating direct-modulated lasers suffer from photon density accumulation at the phase shift point, resulting in spatial hole burning, which alters the refractive index and causes chirping. This leads to dispersion during transmission and low power, limiting their further application. Summary of the Invention

[0004] In view of the above problems, the present invention provides a direct-modulation laser.

[0005] A direct-modulation laser according to an embodiment of the present invention includes: a substrate, an epitaxial layer including a buffer layer, a grating layer, a lower confinement layer, an active layer, an upper confinement layer, an etch stop layer, a cladding layer, and a contact layer sequentially stacked on the substrate; the grating layer has a convex grating structure with a λ / 8 phase shift, the grating layer is located on the N-type doped side, and the convex grating structure with a λ / 8 phase shift is used to reduce the photon density at the phase shift by utilizing the negative mirror loss feedback effect, and to confine the accumulation of holes on the P-type doped side by utilizing the characteristic that the electron mobility is greater than the hole mobility.

[0006] According to an embodiment of the present invention, the period of the grating layer should satisfy:

[0007]

[0008]

[0009] in, The grating period at the non-phase-shifted position. The grating length at the phase shift point. For the Bragg wavelength, The effective refractive index of a laser.

[0010] According to an embodiment of the present invention, the etching depth of the grating layer should satisfy:

[0011]

[0012] in, The etching depth of the convex grating structure at the non-phase-shifted location. This represents the etching depth of the convex grating structure at the phase shift point. This represents the etching depth at the boundary of the convex grating structure. The total length of the convex grating structure. This is the distance between the convex grating structure and the laser's output surface.

[0013] According to an embodiment of the present invention, the etching depth of the convex grating structure at the phase shift satisfies: The etching depth at the boundary of the convex grating structure satisfies .

[0014] According to an embodiment of the present invention, the grating layer is made of InGaAsP and InP, wherein the thickness of InGaAsP is 15nm~55nm and the thickness of InP is 15nm~55nm.

[0015] According to an embodiment of the present invention, the thickness of the etching stop layer is 10 nm to 40 nm; the thickness of the contact layer is 100 nm to 300 nm; the etching medium layer and the contact layer are P-type InGaAsP layers, and the doping concentration of the contact layer is 8 × 10⁻⁶. 18 cm -3 ~2×10 20 cm -3 .

[0016] According to an embodiment of the present invention, the cladding material includes P-type InP, and the cladding thickness is 1.8 μm to 3.8 μm.

[0017] According to an embodiment of the present invention, the material of the lower confining layer includes InGaAlAs, and the thickness of the lower confining layer is 15nm~85nm; the material of the upper confining layer includes InGaAlAs, and the thickness of the upper confining layer is 15nm~85nm.

[0018] According to an embodiment of the present invention, the active layer is made of InGaAlAs and has a thickness of 80nm~150nm.

[0019] According to an embodiment of the present invention, the substrate material includes N-type InP, and the substrate thickness is 75μm to 85μm; the buffer layer material includes N-type InP, and the buffer layer thickness is 200nm to 800nm.

[0020] The direct-modulation laser provided by this invention has at least the following technical effects:

[0021] By introducing a λ / 8 phase shift into the grating of a directly modulated laser and utilizing its negative mirror loss feedback effect, the chirp of the directly modulated laser is reduced, enabling long-distance transmission with low dispersion. Changing the etching depth at different positions of the grating optimizes the coupling coefficient, reduces the spatial hole burning effect, and improves the output power of the directly modulated laser. Furthermore, the grating is located on the N-type doped side, taking advantage of the fact that the electron migration rate is greater than the hole migration rate, resulting in lower parasitic resistance compared to other lasers located on the P-type doped side, thus improving the modulation rate. Attached Figure Description

[0022] The above-described features, other objects, and advantages of the present invention will become clearer from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0023] Figure 1 A schematic diagram of a laser according to an embodiment of the present invention is shown.

[0024] Figure 2 A schematic front view of a grating layer according to an embodiment of the present invention is shown;

[0025] Figure 3 A schematic top view of a grating layer according to an embodiment of the present invention is shown;

[0026] Figure 4 The diagram illustrates the relationship between the grating coupling coefficient and the grating etching depth according to an embodiment of the present invention.

[0027] Reference numerals: 1: Substrate; 2: Buffer layer; 3: Grating layer; 4: Lower confinement layer; 5: Active layer; 6: Upper confinement layer; 7: Etching stop layer; 8: Cladding layer; 9: Contact layer. Detailed Implementation

[0028] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0030] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0031] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0032] Output power and chirp are important performance parameters of directly modulated lasers. Chirp is a crucial characteristic of directly modulated lasers, referring to the phenomenon where the laser frequency changes over time. Due to variations in the injected current, the refractive index of the laser material changes, altering the phase of the light within the medium and causing broadening of the modulation spectrum, resulting in chirp. Chirp can cause dispersion during long-distance light transmission. Dispersion refers to the property of a material's refractive index changing with the frequency of incident light, which can lead to signal distortion and increased bit error rate.

[0033] The coupling coefficient and wavenumber of a grating reflect the magnitude of its feedback effect on light. A larger coupling coefficient results in a stronger feedback effect, while a smaller coupling coefficient leads to a weaker feedback effect. The etching depth of the grating also affects its coupling coefficient; a deeper etching depth results in a larger coupling coefficient, while a shallower etching depth results in a smaller coupling coefficient.

[0034] In the process of developing this invention, the applicant discovered that traditional direct-modulation lasers often employ a λ / 4 phase-shift structure, which offers better single-mode characteristics compared to other gratings. However, due to the feedback effect of the positive mirror loss, the chirping effect is severe. This effect causes dispersion of the laser during transmission, resulting in signal distortion and hindering its use in long-distance communication. Furthermore, when the injected current exceeds the threshold current, spatial hole burning occurs, affecting the laser's output power.

[0035] In view of this, embodiments of the present invention provide a direct-modulated laser that can effectively solve the problems of low power and high transmission dispersion in existing direct-modulated lasers.

[0036] The direct-modulation laser of the present invention will now be described in detail with reference to the accompanying drawings.

[0037] Figure 1 A schematic diagram of a laser according to an embodiment of the present invention is shown.

[0038] like Figure 1As shown, the direct-modulated laser in this embodiment is a semiconductor laser with a convex grating structure having a λ / 8 phase shift, including: a substrate 1 and an epitaxial layer. The epitaxial layer is disposed on the substrate 1 and includes a stacked buffer layer 2, a grating layer 3, a lower confinement layer 4, an active layer 5, an upper confinement layer 6, an etch stop layer 7, a cladding layer 8, and a contact layer 9.

[0039] The structure of grating layer 3 is a convex grating structure with λ / 8 phase shift, and grating layer 3 is located on the N-type doped side.

[0040] The refractive index modulation in a grating is proportional to the coupling coefficient, which in turn is proportional to the etching depth. Using a λ / 8 phase-shift grating can utilize its negative mirror loss feedback effect to reduce the photon density at the phase shift, thus minimizing chirp and meeting the application requirements for long-distance transmission. Furthermore, changing the etching depth can further compensate for the low optical power output of the λ / 8 phase-shift grating due to the spatial hole burning effect. Reducing the etching depth at the phase shift decreases the coupling coefficient, ensuring high-power, single-mode output even under large injection currents.

[0041] The grating layer 3 is located on the N-type doped side. By taking advantage of the fact that the electron mobility is greater than the hole mobility, the accumulation of holes on the P side can be avoided, which would affect the carrier injection into the finite layer and cause the series resistance to increase. This is beneficial to further improve the 3dB bandwidth of the laser.

[0042] In one possible implementation of this embodiment, controlling the etching depth in the form of a sine function curve can ensure that while reducing the photon density in the grating phase shift region, there is sufficient optical feedback, and while reducing chirp, it can ensure high-power output in a single mode.

[0043] Compared to traditional λ / 4 phase-shift gratings, the directly modulated laser of this invention exhibits lower chirp and higher output power. By utilizing the negative mirror loss feedback effect of the λ / 8 phase-shift grating and optimizing the coupling coefficient with a convex grating, the chirp and spatial hole burning effects of the laser are effectively reduced. The grating layer 3 is located on the N-type doped side, and its structure is a convex grating structure with a λ / 8 phase shift, which is beneficial for reducing laser chirp and increasing laser output power.

[0044] Figure 2 A schematic front view of a grating layer according to an embodiment of the present invention is shown. Figure 3 A top view of a grating layer according to an embodiment of the present invention is shown schematically.

[0045] like Figure 2 and Figure 3 As shown, based on the above embodiments, in some embodiments, the period of grating layer 3 should satisfy:

[0046]

[0047]

[0048] in, The grating period at the non-phase-shifted position. The grating length at the phase shift point. For the Bragg wavelength, The effective refractive index of a laser.

[0049] The grating propagation constant at the phase shift is:

[0050]

[0051] The grating propagation constant at the non-phase-shifted position is:

[0052]

[0053] The phase shift experienced is:

[0054]

[0055] A λ / 8 phase shift needs to be introduced, i.e. Substituting into the above formula, we get:

[0056]

[0057] To ensure the introduction of a λ / 8 phase shift, the grating length at the phase shift point should satisfy the above relationship.

[0058] Based on the above embodiments, in some embodiments, the etching depth of the grating layer 3 should satisfy:

[0059]

[0060] in, The etching depth of the convex grating structure at the non-phase-shifted location. This represents the etching depth of the convex grating structure at the phase shift point. This represents the etching depth at the boundary of the convex grating structure. The total length of the convex grating structure. This is the distance between the convex grating structure and the laser's output surface.

[0061] In other embodiments, the etching depth of the convex grating structure at the phase shift satisfies: The etching depth at the boundary of the convex grating structure satisfies .

[0062] Because the coupling coefficient is very small when the etching depth is small, it is difficult to provide sufficient optical feedback. Conversely, when the etching depth is large, the coupling coefficient increases, resulting in excessively strong optical feedback and a spatial burning effect. The setting of the range of T values ​​ensures that the coupling coefficients of the gratings on both sides are large enough to guarantee single-mode output, while also making the grating coupling coefficient at the phase shift point small to avoid the occurrence of spatial hole burning.

[0063] Figure 4 The diagram illustrates the relationship between the grating coupling coefficient and the grating etching depth according to an embodiment of the present invention.

[0064] like Figure 4 As shown, the coupling coefficient increases with increasing etching depth. The total cavity length of the laser ranges from 100μm to 300μm. A shorter cavity length limits the output power and increases the difficulty of cleavage, while a longer cavity length increases the volume of the active region, affecting the laser's bandwidth characteristics.

[0065] In some embodiments, both the corrosion stop layer 7 and the contact layer 9 can be made of p-type InGaAsP material, and their thicknesses are set according to actual requirements. The thickness of the corrosion stop layer 7 can be 10 nm to 40 nm, the thickness of the contact layer 9 can be 100 nm to 300 nm, and the doping concentration of the contact layer can be 8 × 10⁻⁶. 18 cm -3 ~2×10 20 cm -3 .

[0066] In other embodiments, the cladding material may include p-type InP, and the thickness of the cladding is 1.8 μm to 3.8 μm.

[0067] In other embodiments, both the lower confining layer 4 and the upper confining layer 6 can be made of InGaAlAs material, and their thicknesses are set according to actual needs. For example, the thickness of the upper confining layer 6 can be 15nm~85nm, and the thickness of the lower confining layer 4 can be 15nm~85nm.

[0068] In other embodiments, the active layer 5 is made of InGaAlAs and has a thickness of 80 nm to 150 nm.

[0069] In other embodiments, the grating layer 3 can be made of InGaAsP and InP materials, and the thickness of both can be set according to actual needs. For example, the thickness of InGaAsP can be 15nm to 55nm, and the thickness of InP material can be 15nm to 55nm.

[0070] In other embodiments, the substrate 1 may be made of N-type InP, and the thickness of the substrate 1 may be 75 μm to 85 μm. The buffer layer 2 may be made of N-type InP, and the thickness of the buffer layer 2 may be 200 nm to 800 nm.

[0071] To further clarify the description of the directly modulated laser provided by the present invention, the structure of the directly modulated laser is illustrated below with a specific example. It should be understood that this example is not intended to demonstrate the present invention.

[0072] A multilayer structure of a laser is grown by metal-organic chemical vapor deposition. The laser includes a substrate 1, a buffer layer 2, a grating layer 3, a lower confinement layer 4, an active layer 5, an upper confinement layer 6, an etch stop layer 7, a cladding layer 8, and a contact layer 9 stacked together.

[0073] Substrate 1, buffer layer 2 and cladding layer 8 are all made of InP material, grating layer 3 is made of both InGaAsP and InP material, active layer 5, lower confinement layer 4 and upper confinement layer 6 are made of InGaAlAs material, and etch stop layer 7 and contact layer 9 are both made of InGaAsP material.

[0074] The thickness of each layer is set according to requirements; the thickness of substrate 1 is 75nm~85μm, and the thickness of buffer layer 2 is 200nm~800nm.

[0075] The thickness of grating layer 3 is 15nm~65nm, the thickness of lower confinement layer 4 and upper confinement layer 6 is 15nm~85nm, the thickness of active layer 5 is 80nm~150nm, the thickness of etch stop layer 7 is 10nm~40nm, the thickness of cladding layer 8 is 1.8μm~3.8μm, the thickness of contact layer 9 is 100nm~300nm, and the doping concentration of contact layer is 8×10⁻⁶. 18 cm -3 ~2×10 20 cm -3 .

[0076] The etching depth h of the grating varies in the form of a sine function. This improves the coupling coefficient at the phase shift, reduces the occurrence of spatial hole burning, and ensures a sufficiently large coupling coefficient on both sides for optical feedback, thus guaranteeing the single-mode characteristic of the laser.

[0077] By introducing a λ / 8 phase shift at the phase shift point, the chirping phenomenon of the laser can be reduced by utilizing its negative mirror loss feedback effect, thus avoiding dispersion during long-distance signal transmission. Furthermore, by reducing the etching depth at the phase shift point, the spatial hole burning phenomenon of the λ / 8 phase shift grating can be avoided when the injection current increases, thereby further improving the output power of the laser.

[0078] The grating layer 3 is located on the N-type doped side. By taking advantage of the fact that the electron mobility is greater than the hole mobility, the accumulation of holes on the P side can be avoided, which would cause the series resistance to increase. This is beneficial to further improve the bandwidth of the laser.

[0079] The InGaAsP and InP materials in grating layer 3 form refractive index modulation, which has a certain mode screening effect on the laser, so that only wavelengths that meet specific conditions can resonate and be amplified in the cavity.

[0080] The active layer 5 is made of InGaAlAs material with a quantum well structure. The quantum well structure has a high relaxation oscillation frequency and better confinement of electrons, which helps to reduce the threshold current. Combined with the good temperature characteristics and high differential gain of InGaAlAs material, it can further improve the high temperature characteristics and bandwidth performance of the laser.

[0081] The corrosion stop layer 7 can prevent over-corrosion during wet corrosion and protect the upper limiting layer 6 and the active layer 5.

[0082] Contact layer 9 is composed of heavily doped p-type InGaAsP material with a doping concentration of 8 × 10⁻⁶. 18 cm -3 ~2×10 20 cm -3 The purpose of heavy doping is to form an ohmic contact with the P-type electrode on the laser surface, thereby reducing the series resistance.

[0083] In summary, the directly modulated laser provided by this invention reduces the chirp effect by introducing a λ / 8 phase shift in the cavity, thereby reducing dispersion in long-distance communication applications and further promoting the application of directly modulated lasers in information transmission and data transfer. The grating layer 3, located on the N-type doped side, effectively reduces parasitic resistance and increases the modulation rate by utilizing the high electron mobility. The coupling coefficient of the grating is closely related to its etching depth. By adjusting the etching depth of the grating layer 3, the coupling coefficient of the grating can be adjusted, reducing the spatial hole-burning effect of the λ / 8 phase-shift grating, and further improving the laser's output power while reducing chirp.

[0084] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems and methods according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing the specified logical function. It should also be noted that in some alternative implementations, the functions indicated in the blocks may occur in a different order than those indicated in the drawings. For example, two consecutively indicated blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram or flowchart, and combinations of blocks in a block diagram or flowchart, may be implemented using a dedicated hardware-based system that performs the specified function or operation, or using a combination of dedicated hardware and computer instructions.

[0085] Those skilled in the art will understand that the features described in the various embodiments and / or claims of the present invention can be combined or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments and / or claims of the present invention can be combined or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

[0086] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of the invention is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A direct modulated laser, characterized by Comprise: a substrate, an epitaxial layer comprising a buffer layer, a grating layer, a lower confinement layer, an active layer, an upper confinement layer, a etching stop layer, a cladding layer and a contact layer which are sequentially stacked on the substrate; the grating layer is of a convex grating structure with a phase shift of λ / 8, the grating layer is located on the N-type doped side, the convex grating structure with a phase shift of λ / 8 is used to reduce the photon density at the phase shift by using the negative mirror loss feedback effect, and to limit the accumulation of holes on the P-type doped side by using the characteristic that the electron mobility is greater than the hole mobility.

2. The direct modulation laser of claim 1, wherein, The period of the grating layer should satisfy: wherein, is the grating period at non-phase shift, is the grating length at phase shift, is the Bragg wavelength, is the effective refractive index of the laser.

3. The direct modulated laser of claim 1, wherein, The etching depth of the grating layer should satisfy: wherein, is the etching depth of the convex grating structure at non-phase shift, is the etching depth of the convex grating structure at phase shift, is the etching depth of the convex grating structure at the boundary of the convex grating structure, is the total length of the convex grating structure, is the distance of the convex grating structure from the laser light output surface.

4. The direct modulation laser of claim 3, wherein, The etching depth of the phase-shifted convex grating structure satisfies: The etching depth of the convex grating structure boundary satisfies .

5. The direct modulated laser of any of claims 1-4, wherein, The material of the grating layer includes InGaAsP and InP, the thickness of the InGaAsP is 15nm~55nm, and the thickness of the InP is 15nm~55nm.

6. The direct modulated laser of any of claims 1-4, wherein, The thickness of the etching stop layer is 10nm~40nm; The thickness of the contact layer is 100nm~300nm; The corrosion medium layer and the contact layer are P-type InGaAsP layers, the doping concentration of the contact layer is 8x10 18 cm -3 ~2x10 20 cm -3 .

7. The direct modulated laser of any of claims 1-4, wherein, The material of the cladding layer includes P-type InP, and the thickness of the cladding layer is 1.8μm~3.8μm.

8. The direct modulated laser of any of claims 1-4, wherein, The material of the lower confinement layer includes InGaAlAs, and the thickness of the lower confinement layer is 15nm~85nm; the material of the upper confinement layer includes InGaAlAs, and the thickness of the upper confinement layer is 15nm~85nm.

9. The direct modulated laser of any of claims 1-4, wherein, The material of the active layer includes InGaAlAs, and the thickness of the active layer is 80nm~150nm.

10. The direct modulated laser of any of claims 1-4, wherein, The material of the substrate includes N-type InP, and the thickness of the substrate is 75μm~85μm; the material of the buffer layer includes N-type InP, and the thickness of the buffer layer is 200nm~800nm.

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