Electroabsorption modulated laser, buried heterostructure electroabsorption modulated laser, and ridge waveguide electroabsorption modulated laser

Abstract

An electroabsorption modulation laser (EML) device features a deployed modulator to improve the modulation efficiency and the steepness of the transmission curve. The EML device typically includes a laser segment, such as a distributed feedback (DFB) laser segment, an electroabsorption modulator (EAM) segment, and an isolation segment between the laser segment and the EAM segment. The EML device also includes an active region containing quantum well structures located within the laser segment and the EAM segment. The mesa segment spans the laser segment, the isolation segment, and the EAM segment and is deployed, such that at least a portion of the isolation mesa segment narrows outwards, and at least a portion of the modulator mesa segment narrows inwards. The EML device can be a ridge waveguide (RWG) type EML device or a buried heterostructure (BH) type EML device.

Description

Technical Field

[0001] This invention relates to semiconductor lasers, and more particularly, to an electro-absorption modulated laser (EML) device with a spread modulator. Background Technology

[0002] Semiconductor lasers can be used in optical communication and data processing applications (such as data centers). In optical communication, for example, semiconductor lasers can be used in transmitter optical subassemblies (TOSAs) to transmit optical signals. Electro-absorption modulated lasers (EMLs) may have advantages over direct modulated lasers (DMLs), such as relatively lower chromatic dispersion. Despite these advantages, the ever-increasing speed and frequency demands of optical communication and data processing have posed challenges to EMLs, especially during high-power and / or high-speed operation. Summary of the Invention

[0003] According to one aspect of the invention, an electro-absorption modulated laser (EML) device includes a laser segment, an electro-absorption modulator (EAM) segment, and an isolation segment located between the laser segment and the EAM segment. An active region is located within the laser segment and the EAM segment, wherein the active region includes a quantum well structure. A mesa segment extends across the laser segment, the isolation segment, and the EAM segment. The mesa segment includes a laser mesa segment located within the laser segment, an isolation mesa segment located within the isolation segment, and an EAM mesa segment located within the EAM segment. The EAM mesa segment is unfolded such that at least a portion of the isolation mesa segment narrows outward and at least a portion of the EAM mesa segment narrows inward.

[0004] According to another aspect of the invention, a buried heterostructure (BH) EML device includes a laser section, an electro-absorption modulator (EAM) section, and an isolation section located between the laser section and the EAM section. A mesa section extends across the top of the laser section, the isolation section, and the EAM section. The mesa section includes a laser mesa section located in the laser section, an isolation mesa section located in the isolation section, and an EAM mesa section located in the EAM section. The mesa section is extended such that at least a portion of the isolation mesa section narrows outward and at least a portion of the EAM mesa section narrows inward. An active region is located between the laser section and the EAM section and is limited on both sides by a BH-type configuration.

[0005] According to another aspect of the invention, a ridge-waveguide (RWG) EML device includes a laser segment, an electro-absorption modulator (EAM) segment, and an isolation segment located between the laser segment and the EAM segment. A mesa segment extends across the top of the laser segment, the isolation segment, and the EAM segment. The mesa segment includes a laser mesa segment located within the laser segment, an isolation mesa segment located within the isolation segment, and an EAM mesa segment located within the EAM segment. The mesa segment is extended such that at least a portion of the isolation mesa segment narrows outward and at least a portion of the EAM mesa segment narrows inward. An active region is located between the laser segment and the EAM segment and has an RWG-type configuration located below the mesa segment. Attached Figure Description

[0006] These and other features and advantages will become clearer by reading the following detailed description, in conjunction with the accompanying drawings:

[0007] Figure 1 This is a schematic perspective view of an electro-absorption modulated laser (EML) device with a deployable modulator, consistent with an embodiment of the present invention.

[0008] Figure 2 This is a schematic side cross-sectional view of an EML device including a deployable modulator, consistent with an embodiment of the present invention.

[0009] Figure 3 This is a schematic top view of an EML device with a deployable modulator, consistent with an embodiment of the present invention.

[0010] Figure 4This is a graph showing the exponential decay of the photocurrent density along the cavity of the electro-absorption (EA) modulator.

[0011] Figure 5 This is a schematic top view of an example of a deployable modulator that can be used in an EML device, consistent with the present invention.

[0012] Figure 6 For having Figure 5 A diagram showing the power transfer in the EML device of the expandable modulator.

[0013] Figure 7 For having Figure 5 A graph showing the refractive index in the EML device of the expandable modulator.

[0014] Figure 8 For having Figure 5 A diagram showing the modal distribution in the EML device of the expandable modulator.

[0015] Figure 9 For having Figure 5 A diagram showing the optical limitations in the EML device of the expandable modulator.

[0016] Figure 10 For having Figure 5 A diagram showing the modal propagation in the XZ plane in the EML device of the expanded modulator.

[0017] [Explanation of Labels in the Attached Image]

[0018] 100: Electro-absorption modulation laser device

[0019] 102: Deploy modulator

[0020] 110: Laser Section

[0021] 120: Isolation Section

[0022] 130: Electrical absorption modulator section

[0023] 140: Countertop Section

[0024] 142: Laser-etched tabletop section

[0025] 144: Isolation Platform Section

[0026] 145: Part

[0027] 146: Electro-absorption modulator platform section

[0028] 147: Unnarrowed portion

[0029] 148: Part

[0030] 149: Unnarrowed section

[0031] 150: Active Area

[0032] 152: Distributed Feedback Grating

[0033] 154: High-reflectivity coating

[0034] 156: Anti-reflective coating

[0035] 160: Laser contact

[0036] 162: Modulator contact

[0037] 170: Laser Beam

[0038] 400: Potential carrier stacking region

[0039] 502: Deploy modulator

[0040] 546: Electrical absorption modulator section

[0041] 548: Narrowing section

[0042] 549: Unnarrowed portion

[0043] L1: First Length

[0044] L2: Second Length

[0045] L3: Third Length

[0046] L4: Fourth Length

[0047] L5: Fifth Length

[0048] W1: First width

[0049] W2: Second width

[0050] W3: Third Width

[0051] X, Y, Z: Axes Detailed Implementation

[0052] According to embodiments of the present invention, an electro-absorption modulated laser (EML) device has an expanded modulator to improve the modulation efficiency and propagation curve steepness of the EML device. The EML device typically includes a laser segment, such as a distributed feedback (DFB) laser segment, an electro-absorption modulator (EAM) segment, and an isolation segment located between the laser segment and the EAM segment. The EML device also includes an active region comprising quantum well structures located in the laser segment and the EAM segment. A mesa segment extends across the laser segment, the isolation segment, and the EAM segment and is expanded such that at least a portion of the isolation mesa segment narrows outward and at least a portion of the modulator mesa segment narrows inward. The EML device can be a ridgewaveguide (RWG) type EML device or a buried heterostructure (BH) type EML device.

[0053] For optical communications using EML devices, a high extinction ratio (ER) and a steep transmission profile are generally desirable. ER represents the ratio of two optical power levels of the digital signal generated by the EML device, and the transmission profile represents the EML output power as a function of the bias voltage. A steeper transmission profile can help increase the ER and reduce the peak-to-peak modulation voltage (Vpp).

[0054] To achieve high ER and steep transport curves, EML devices can utilize the quantum-confined stark effect (QCSE) in the EAM segment of a multiple quantum well (MQW) structure. However, the high power and / or high speed of EML devices may approach the QCSE limit. QCSE refers to the phenomenon where an electric field applied to the energy levels of electrons and holes (i.e., carriers) within the quantum well alters the absorption spectrum, resulting in changes in optical absorption characteristics, which can be used to modulate optical signals by varying the applied voltage. The transport of carriers leaving and entering the quantum well affects the modulation rate of the quantum well's EAM. However, at higher speeds and / or higher power, carriers may not completely leave the quantum well and remain trapped within it, which can significantly worsen the QCSE effect.

[0055] The overall carrier lifetime is determined by two main carrier escape mechanisms—thermo-ion emission and tunneling. Thermionic emission refers to high-energy carriers crossing the quantum well barrier, while tunneling refers to carriers with lower energies crossing the barrier through tunnels. For example, in InGaAsP material systems, hole carriers may have more difficulty escaping, and the lifetime of hole tunneling is much longer than that of thermionic emission. The barrier height (i.e., the energy difference between the bottom of the quantum well and the surrounding barrier material) has the most significant impact on carrier escape time.

[0056] The lifetime of carriers in a quantum well is closely related to the concentration of photogenerated holes accumulated within that quantum well. The two-dimensional photogenerated carrier density can be expressed as follows:

[0057]

[0058] in Photocurrent density, For the total carrier lifetime in the quantum well, and This represents electron charge. Therefore, the photocurrent density... The output power of EAM light increases proportionally. The adverse effects of carrier accumulation in EML devices may include: electric field shielding, resulting in a reduction in QCSE energy shift within the electric field; QCSE modulation saturation, limiting the tolerable incident light intensity; and bandwidth limited by photogenerated carrier transmission.

[0059] Existing techniques for reducing carrier packing in EML devices include reducing total carrier lifetime. and reduce photocurrent density However, these methods involve trade-offs. Reducing the overall carrier lifetime... Using a shallow well (e.g.) will suppress the steepness of the transfer curve, especially at higher operating voltages. This reduces the photocurrent density. This reduces incident power, thereby lowering EML optical power, and increases the modulator mesa width, reducing RC bandwidth. Shorter EAM cavities (e.g., to provide higher modulation speed / frequency) and increased power pose additional challenges to reducing carrier packing and improving the ER of the EML device.

[0060] like Figure 4 The photocurrent density along the EAM cavity is shown. In the figure, the potential carrier packing region 400 is mainly located within a few micrometers on the input side of the EAM cavity. The non-uniform mesa width that unfolds on the input side of the EAM cavity reduces carrier packing in this region, thereby increasing the steepness of the transport curve and reducing the peak-to-peak modulation voltage. This design provides more degrees of freedom and tolerance for deep quantum well structures in the EAM.

[0061] Reference Figures 1 to 3The EML device 100 with the expandable modulator 102 will be described in more detail below, consistent with the embodiments of the present invention. As described above, the expandable modulator 102 reduces the photon current density on the input side, thereby reducing carrier accumulation in the quantum well and avoiding QCSE modulation saturation and electric field shielding effects. The EML device 100 with the expandable modulator 102 may have a ridge waveguide (RWG) configuration or a buried heterostructure (BH) configuration, as is known to those skilled in the art.

[0062] EML device 100 includes a laser section 110, an electro-absorption modulator (EAM) section 130, and an isolation section 120 located between the laser section 110 and the EAM section 130. EML device 100 also includes a mesa section 140 extending across the laser section 110, the isolation section 120, and the EAM section 130. In semiconductor lasers, a mesa is generally a raised region used as a waveguide to confine laser light within a specific area, thereby defining the propagation path and emission profile of the laser light. Mesa section 140 includes a laser mesa section 142, an isolation mesa section 144, and an EAM mesa section 146. The EAM mesa section 146 is expanded such that at least a portion 145 of the isolation mesa section 144 narrows outward and at least a portion 148 of the EAM mesa section 146 narrows inward.

[0063] like Figure 2 As shown, the EML device 100 also includes an active region 150 located at least in the laser section 110 and the EAM section 130. The active region 150 includes a quantum well structure, such as a multiple quantum well (MQW) structure. In an RWG-type EML device, the active region 150 may be located below a mesa (also called a ridge) formed by etching a top cladding layer. In an RWG-type EML device, a silicate layer may be deposited to block current flow, allowing current to enter only through the ridge, and the cladding material used for the ridge may have a higher refractive index than silicate, resulting in a higher modal index beneath the ridge, thereby guiding optical modes laterally. In a BH-type EML device, the active region 150 may be completely buried by multiple layers of low-refractive-index material to allow for strong mode confinement. The active region 150 and other layers in the EML device 100 may be configured and formed using materials and techniques known to those skilled in the art.

[0064] In this embodiment, the laser section 110 of the EML device 100 may include a distributed feedback (DFB) laser section, such as a DFB grating 152. The EML device 100 may include a highly reflective (HR) coating 154 at one end of the laser section 110 to allow light to be internally reflected, and an anti-reflective (AR) coating 156 at the output end of the EAM section 130 to allow light to exit. The HR coating 154 may, for example, contain SiO2 / TaOx, while the AR coating 156 may, for example, contain SiNOx.

[0065] The EML device 100 may include laser contacts 160 in the laser section 110 to receive laser bias current and modulator contacts 162 in the EAM section 130 to receive modulation voltage. The laser bias current causes laser light to be generated in the laser section 110, and the modulation voltage causes the laser light to be modulated in the EAM section 130. The modulated laser light 170 passes through the AR coating 156 and is output from the EML device 100.

[0066] In the EML device 100 of this embodiment, such as Figure 3 As shown, the EAM table section 146 includes an unnarrowed portion 149 at the output end, having a first width W1 and a first length L1. An inwardly narrowing portion 148 preceding the unnarrowed portion 149 gradually narrows from a second width W2 to a first width W1 within a second length L2. The EAM table section 146 may optionally include another unnarrowed portion 147 preceding the inwardly narrowing portion 148, having a second width W2 and a third length L3. An outwardly narrowing portion 145 of the isolation table section 144 gradually narrows from a third width W3 to a second width W2 within a fourth length L4, while the laser table section 142 has a third width W3 and a fifth length L5. The second width W2 of the narrowing portion 148 of the EAM table section 146 may be 1.5 to 5 times the first width W1 of the unnarrowed portion 149, and more specifically, 2 to 4 times.

[0067] The transition from the outward narrowing portion of the isolation tabletop section 145 to the inward narrowing portion 148 of the EAM tabletop section 146 can be designed to minimize propagation loss. Although the transition of the tabletop width is illustrated as linear, this is not a limitation, and the narrowing portion 148 of the EAM tabletop section 146 can also have a non-linear transition.

[0068] The first length L1, second length L2, and third length L3 of the EAM mesa segment 146 can be optimized for optical confinement, absorption, and bandwidth. In some embodiments, the first length L1 can be in the range of 60 to 200 µm, the second length L2 can be in the range of 20 to 100 µm, the third length L3 can be in the range of 0 to 20 µm, and the total modulator length (L1+L2+L3) can be in the range of 80 to 220 µm. The fourth length L4 of the isolation mesa segment 144 can be in the range of 20 to 80 µm, and the fifth length L5 of the laser mesa segment 142 can be in the range of 250 to 500 µm. The first width W1 can be in the range of 1 to 3 µm, the second width W2 can be in the range of 1.5 to 5 µm, and the third width W3 can be in the range of 1.5 to 2.5 µm.

[0069] Reference Figures 5 to 10 A more detailed description of a design example of the deployable modulator 502 is provided below. This design of the deployable modulator 502 can be implemented in an EML device with an RWG configuration or a BH configuration, as described above. Figure 5 A schematic top view of the deployable modulator 502 located in the EAM segment 546 of the EML device is shown, wherein the X-axis extends along the width of the EAM segment 546, the Z-axis extends along the length of the EAM segment 546, and the Y-axis extends along the height of the EAM segment 546. In this example, the deployable modulator 502 includes a narrowed portion 548 having a length L2 of 35 µm and an unnarrowed portion 549 having a length L1 of 97 µm. The width of the narrowed portion 548 gradually narrows from 3 µm of a second width W2 to 1.5 µm of a first width W1.

[0070] Figure 6 This displays the percentage of power transferred along the propagation direction (e.g., along the Z-axis) of the RWG-type EML device containing the expandable modulator 502 in the narrowing section 548. Figure 7 Displays the refractive index of an RWG-type EML device with expandable modulator 502 along the X and Y directions. Figure 8 This displays the modal distribution of an RWG-type EML device with expandable modulator 502 along the X and Y directions. Figure 9 This displays the percentage of light confinement along the propagation direction (e.g., along the Z-axis) of the narrowing portion 548 of the RWG-type EML device with expandable modulator 502. Figure 10 The diagram shows the modal propagation of the EML with expandable modulator 502 in the XZ plane along the propagation direction of the inclined portion 548. This example of expandable modulator 502 provides progressive propagation with up to 98% power transfer and negligible changes in optical confinement, for example, compared to a non-narrowed modulator.

[0071] Accordingly, embodiments of the EML device with a deployable modulator of the present invention can improve the modulation efficiency and transmission curve steepness of the EML device with minimal propagation loss even at higher speeds and / or higher power.

[0072] While the principles of the invention have been described herein, those skilled in the art should understand that this description is merely illustrative and not intended to limit the scope of the invention. In addition to the exemplary embodiments shown and described herein, other embodiments falling within the scope of the invention are conceived. Modifications and substitutions made by those skilled in the art should be considered to fall within the scope of the invention.

Claims

1. An electro-absorption modulation laser device, characterized in that, Include One laser section; One section of the electric absorption modulator; An isolation section is located between the laser section and the electro-absorption modulator section; An active region is located between the laser section and the electro-absorption modulator section, wherein the active region includes a quantum well structure; and A platform segment extends across the laser segment, the isolation segment, and the electro-absorption modulator segment, wherein the platform segment includes a laser platform segment located in the laser segment, an isolation platform segment located in the isolation segment, and an electro-absorption modulator platform segment located in the electro-absorption modulator segment, and wherein the electro-absorption modulator platform segment is extended such that at least a portion of the isolation platform segment narrows outward and at least a portion of the electro-absorption modulator platform segment narrows inward.

2. The electro-absorption modulation laser device as described in claim 1, characterized in that, It further includes a high-reflectivity coating applied to one end of the laser section and an anti-reflectivity coating applied to one output end of the electro-absorption modulator section.

3. The electro-absorption modulation laser device as described in claim 1, characterized in that, The laser section contains a distributed feedback laser section.

4. The electro-absorption modulation laser device as described in claim 1, characterized in that, At least a portion of the electro-absorption modulator platform section has a fixed width before narrowing inward.

5. The electro-absorption modulation laser device as described in claim 1, characterized in that, The electro-absorption modulator platform section has a first width W1 on an output side near the laser, and the electro-absorption modulator platform section narrows from a second width W2 to the first width W1, wherein the second width W2 is greater than the first width W1.

6. The electro-absorption modulation laser device as described in claim 5, characterized in that, The second width W2 is 1.5 to 5 times larger than the first width W1.

7. The electro-absorption modulation laser device as described in claim 6, characterized in that, The second width W2 is 2 to 4 times larger than the first width W1.

8. The electro-absorption modulation laser device as described in claim 5, characterized in that, At least a portion of the electro-absorption modulator platform section has the second width W2 before narrowing inward.

9. The electro-absorption modulation laser device as described in claim 5, characterized in that, The electro-absorption modulator platform section narrows linearly from the second width W2 to the first width W1.

10. The electro-absorption modulation laser device as described in claim 5, characterized in that, The first width W1 is in the range of 1 to 3 micrometers and the second width W2 is in the range of 1.5 to 5 micrometers.

11. The electro-absorption modulation laser device as described in claim 10, characterized in that, The laser-etched platform section has a third width W3 ranging from 1.5 to 2.5 micrometers.

12. The electro-absorption modulation laser device as described in claim 10, characterized in that, The electro-absorption modulator platform section with the first width W1 has a first length L1, the narrowed electro-absorption modulator platform section has a second length L2, the electro-absorption modulator platform section with the second width W2 has a third length L3, the outwardly narrowed isolation platform section has a fourth length L4, and the laser platform section has a fifth length L5.

13. The electroabsorption modulation laser device as described in claim 12, characterized in that, The first length L1 is in the range of 60 to 200 micrometers, the second length L2 is in the range of 20 to 100 micrometers, and the third length L3 is in the range of 0 to 20 micrometers.

14. The electro-absorption modulation laser device as described in claim 13, characterized in that, The fourth length L4 is in the range of 20 to 80 micrometers and the fifth length L5 is in the range of 250 to 500 micrometers.

15. The electro-absorption modulation laser device as described in claim 1, characterized in that, The electroabsorption modulation laser device has a hidden heterostructure configuration.

16. The electro-absorption modulation laser device as described in claim 1, characterized in that, The electroabsorption modulation laser device has a ridge waveguide configuration.

17. A concealed heterostructure electro-absorption modulation laser device, characterized in that, Include: One laser section; One section of the electric absorption modulator; An isolation section is located between the laser section and the electro-absorption modulator section; A platform section extending across the top of the laser section, the isolation section, and the electro-absorption modulator section, wherein the platform section includes a laser platform section in the laser section, an isolation platform section in the isolation section, and an electro-absorption modulator platform section in the electro-absorption modulator section, and wherein the platform section is unfolded such that at least a portion of the isolation platform section narrows outward and at least a portion of the electro-absorption modulator platform section narrows inward; and An active region is located between the laser section and the electro-absorption modulator section, wherein the active region is constrained on both sides by a hidden heterostructure configuration.

18. The buried heterostructure electro-absorption modulation laser device as described in claim 17, characterized in that, At least a portion of the electro-absorption modulator platform section has a fixed width before narrowing inward.

19. The buried heterostructure electro-absorption modulation laser device as described in claim 17, characterized in that, The electro-absorption modulator platform section has a first width W1 on an output side near the laser, and the electro-absorption modulator platform section narrows from a second width W2 to the first width W1, wherein the second width W2 is 1.5 to 5 times larger than the first width W1.

20. A ridge wave conductive absorption modulation laser device, characterized in that, Include One laser section; One section of the electric absorption modulator; An isolation section is located between the laser section and the electro-absorption modulator section; A platform section extends across the top of the laser section, the isolation section, and the electro-absorption modulator section, wherein the platform section includes a laser platform section located in the laser section, an isolation platform section located in the isolation section, and an electro-absorption modulator platform section located in the electro-absorption modulator section, and wherein the platform section is unfolded such that at least a portion of the isolation platform section narrows outward and at least a portion of the electro-absorption modulator platform section narrows inward; as well as An active region is located between the laser section and the electro-absorption modulator section, wherein the active region is located below the platform section and has a ridge waveguide configuration.

21. The ridge wave conductive absorption modulation laser device as described in claim 20, characterized in that, At least a portion of the electro-absorption modulator platform section has a fixed width before narrowing inward.

22. The ridge wave conductive absorption modulation laser device as described in claim 20, characterized in that, The electro-absorption modulator platform section has a first width W1 on an output side near the laser, and the electro-absorption modulator platform section narrows from a second width W2 to the first width W1, wherein the second width W2 is 1.5 to 5 times larger than the first width W1.

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