A semiconductor optical amplifier with an N-doped active layer based on silicon photonics.

Abstract

A semiconductor optical amplifier for high-power operation includes a gain medium with a multilayer structure, wherein a P-layer, an active layer, and an N-layer are sequentially arranged from top to bottom in its cross-section. The gain medium extends with a length L from the front side to the back side. The active layer includes multiple well layers formed of undoped semiconductor material and multiple barrier layers formed of n-doped semiconductor material. Each well layer is sandwiched between a pair of barrier layers. The front side is characterized by a first reflectivity Rf, while the back side is characterized by a second reflectivity Rb. The mirror loss α of the gain medium is... m Approximately 40-200cm ‑1 It is given by the following formula: α m = (1 / 2L)ln{1 / (Rf×Rb)}.

Description

Technical Field

[0001] This invention relates to optical communication technology. More specifically, this invention provides a semiconductor optical amplifier based on a silicon photonics platform for high-power, high-temperature operation. Background Technology

[0002] Over the past few decades, the use of communication networks has exploded. In the early days of the internet, popular applications were limited to email, bulletin boards, and were mostly informational and text-based web browsing, with relatively small amounts of data transmitted. Today, the internet and mobile applications require massive amounts of bandwidth to transmit photos, videos, music, and other multimedia files. For example, social networks like Facebook process over 500TB of data daily. This high demand for data and data transmission necessitates improvements to existing data communication systems to meet these needs.

[0003] Broadband DWDM (Dense Wavelength Division Multiplexing) optical transmission at data rates of 40 Gbit / s and subsequently 100 Gbit / s over existing single-mode fiber is the goal of next-generation fiber optic communication networks. Recently, optical components have been integrated onto silicon substrates for the fabrication of large-scale photonic integrated circuits that coexist with microelectronic chips. A range of photonic components, including filters, (de)multiplexers, splitters, modulators, and photodetectors, have been demonstrated, primarily on silicon photonic platforms. Silicon photonic platforms on silicon-on-insulator substrates are particularly suitable for the standard WDM communication bands of 1300 nm and 1550 nm because silicon (n = 3.48) and its oxide SiO2 (n = 1.44) are transparent and form high-contrast, highly confined waveguides, which are ideal for medium-to-high integration silicon photonic integrated circuits (SPICs).

[0004] Semiconductor optical amplifiers (SOAs) in silicon photonics platforms have been implemented for numerous applications in optical communications. For example, wavelength-tunable lasers based on SOAs are provided as key components in SPICs for broadband optical communications with improved spectral efficiency. However, developing high-power SOAs or reflective semiconductor optical amplifiers (RSOAs) for elevated temperature operation presents technical challenges in broadband high-speed data communication applications. Therefore, improved technologies are needed. Summary of the Invention

[0005] This invention relates to optical communication technology. One aspect of the invention provides a reflective semiconductor optical amplifier (RSOA) and / or a semiconductor optical amplifier (SOA) for a tunable laser with high power operating at elevated temperatures. More specifically, the invention provides a gain medium having an n-type doped active layer applied in the RSOA / SOA to provide high saturation power at elevated temperatures for fabricating broadband wavelength-tunable lasers for high-speed data communication applications, although other applications are possible.

[0006] In one embodiment, the present invention provides a semiconductor optical amplifier for high-power operation. The semiconductor optical amplifier includes a gain medium comprising a multilayer structure in which a P-layer, an active layer, and an N-layer are sequentially arranged from top to bottom in a cross-section, extending with a length L from its front side to its back side. The active layer comprises a plurality of well layers formed of undoped semiconductor material and a plurality of barrier layers formed of n-doped semiconductor material. Each well layer is sandwiched between a pair of barrier layers. The front side is characterized by a first reflectivity Rf, while the back side is characterized by a second reflectivity Rb. The mirror loss α of the gain medium... m Approximately 40-200cm -1 It is given by the following formula: α m = (1 / 2L)ln{1 / (Rf×Rb)}.

[0007] Optionally, the gain medium is configured to generate at least greater than 15 dBm of saturation power at operating temperatures up to 50°C.

[0008] Optionally, the active layer includes multiple barrier layers with a width of about 5-15 nm and a band gap of about 0.9-1.1 eV.

[0009] Optionally, each barrier layer includes a modulation doped region, wherein the n-type doping concentration ranges from 1.0 × 10⁻⁶. 18 cm -3 ~3.0×10 18 cm -3 The width is 7nm to 10nm.

[0010] Optionally, the active layer comprises multiple well layers with a width of approximately 4-8 nm and a band gap within the corresponding amplification wavelength range. For the C-band, the band gap is approximately 0.8 eV.

[0011] Optionally, the gain medium has a length L of 1 mm and a length greater than 45-100 cm. -1 The mirror loss is reduced because the front side has an anti-reflective coating with a first reflectivity Rf of about 0.005% or less, and the back side has a high reflectivity coating with a second reflectivity Rb greater than 90%, for forming a reflective semiconductor optical amplifier.

[0012] Optionally, the gain medium is configured to amplify the stimulated emission optical cavity in the active layer, wherein the stimulated emission is reflected from the back side and emitted from the front side.

[0013] Optionally, the active layer is made of a linear waveguide passing through the optical cavity, wherein the linear waveguide forms a non-perpendicular angle with respect to the front side and a substantially perpendicular angle with respect to the back side.

[0014] Optionally, the gain medium has a length L of 1 mm and a value greater than 90-200 cm. -1 The mirror loss is reduced because the front side is provided with an anti-reflective coating having a first reflectivity Rf of about 0.005% or less, and the back side is provided with an anti-reflective coating having a second reflectivity Rb of about 0.005% or less, for forming a symmetrical semiconductor optical amplifier.

[0015] Optionally, the gain medium is configured as an optical cavity for amplifying laser light in an active layer, wherein the laser light is incident once from the back side and exits from the front side.

[0016] Optionally, the active layer is made of a linear waveguide passing through the optical cavity, wherein the linear waveguide forms a non-perpendicular angle with respect to the front side and a non-perpendicular angle with respect to the back side.

[0017] Optionally, the P layer includes a p-type confinement layer attached to the upper part of the active layer and a p-type cladding layer attached to the p-type confinement layer on the side further away from the active layer.

[0018] Optionally, the p-type confinement layer includes a first confinement sublayer and a second confinement sublayer. The first confinement sublayer has a thickness of 5-15 nm and a band gap of about 0.9-1.1 eV, and is attached to a barrier layer with a slightly smaller band gap of about 0.9-1.1 eV immediately above the active layer. The second confinement sublayer has a thickness of 15-25 nm and a band gap of about 1.1-1.2 eV, and is attached to the side of the first confinement sublayer further away from the active layer.

[0019] Optionally, the N-layer includes an n-type confinement layer attached to the lower part of the active layer and an n-type cladding layer attached to the side of the n-type confinement layer further away from the active layer.

[0020] Optionally, the n-type confinement layer includes a first confinement sublayer and a second confinement sublayer. The first confinement sublayer has a thickness of 5-15 nm with a band gap of about 0.9-1.1 eV and is attached to a barrier layer with a slightly smaller band gap of about 0.9-1.1 eV immediately below the active layer. The second confinement sublayer has a thickness of 15-80 nm and a band gap of about 1.1-1.2 eV and is attached to the side of the first confinement sublayer further away from the active layer.

[0021] In an alternative embodiment, the present invention provides a wavelength-tunable laser for a silicon photonics platform for high-power operation. The wavelength-tunable laser includes a silicon photonic substrate. Furthermore, the wavelength-tunable laser includes a first semiconductor optical amplifier on the silicon photonic substrate as described herein. A gain medium is configured as an optical cavity having an anti-reflective coating on its front side and a highly reflective coating on its back side to generate laser light amplified in its active layer and reflected by the back side before passing through the front side. The wavelength-tunable laser also includes a wavelength tuner formed in the silicon photonic substrate and configured to receive the laser light via a first waveguide and tune the wavelength of the laser light over a wide bandwidth. Furthermore, the wavelength-tunable laser includes a wavelength locker formed in the silicon photonic substrate and configured to couple with the wavelength tuner and lock the wavelength of the laser light and transmit the laser light via a second waveguide. Additionally, the wavelength-tunable laser includes a second semiconductor optical amplifier on the silicon photonic substrate as described herein. The gain medium is configured as an optical cavity with an anti-reflective coating on both the front and back sides. The laser is input through the back side and amplified in its active layer before being output through the front side.

[0022] Optionally, the active layer in the gain medium of the first semiconductor optical amplifier includes multiple well layers and multiple barrier layers. The multiple well layers are formed of an undoped semiconductor material with a thickness of 6 nm and a band gap within the corresponding amplification wavelength range. The multiple barrier layers are formed of a material with a thickness of 5-15 nm, a band gap of 0.9-1.1 eV, and a doping concentration of 1.0 × 10⁻⁶. 18 cm -3 Up to 3.0×10 18 cm -3 The n-doped semiconductor is formed. Each well layer is sandwiched between a pair of barrier layers.

[0023] Optionally, the active layer in the gain medium of the second semiconductor optical amplifier includes multiple well layers and multiple barrier layers. The multiple well layers are formed of undoped semiconductor material with a thickness of 4-8 nm and a band gap within the corresponding amplification wavelength range. The multiple barrier layers are formed of material with a doping concentration of 1.0 × 10⁻⁶. 18 cm -3 Up to 3.0×10 18 cm -3 It is formed by doped semiconductor material with a thickness of 5nm-15nm and a band gap of 0.9eV-1.1eV; each well layer is sandwiched between a pair of barrier layers.

[0024] Optionally, the gain medium of the first semiconductor optical amplifier has a length of approximately 45 cm for a length of 1 mm. -1 -100cm -1 The mirror loss; the gain medium of the second semiconductor optical amplifier has a length of approximately 90 cm for a length of 1 mm. -1 -200cm -1Mirror wear.

[0025] Optionally, the gain medium of the first semiconductor optical amplifier is configured to generate a saturated laser power of at least 15 dBm at an elevated operating temperature of 50°C, and the gain medium of the second semiconductor optical amplifier is configured to generate a maximum optical power of at least 15 dBm at an elevated operating temperature of 50°C.

[0026] This invention achieves these and other advantages within the context of known techniques for semiconductor optical amplifiers, optionally providing a gain medium comprising a modulated n-doped active layer between PN junctions extending in the form of a waveguide along its length from the front to the back. However, a further understanding of the nature and advantages of the invention can be achieved by referring to the latter part of the specification and the accompanying drawings. Attached Figure Description

[0027] The following illustrations are merely examples and should not unduly limit the scope of the claims herein. Those skilled in the art will recognize many other variations, modifications, and substitutions. It should also be understood that the embodiments and examples described herein are for illustrative purposes only, and various modifications or variations made thereto will be implied to those skilled in the art and are included within the spirit of this process and the scope of the appended claims.

[0028] Figure 1 This is a schematic diagram of a tunable laser based on a combination of a semiconductor optical amplifier (SOA) and a reflective semiconductor optical amplifier (RSOA) according to an embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram of an RSOA with a gain medium in top and side views according to an embodiment of the present invention.

[0030] Figure 3 This is a schematic diagram of an SOA with a gain medium according to an embodiment of the present invention, viewed from the top and side.

[0031] Figure 4 This is a simplified bandgap diagram of the modulation n-doped active layer in the gain medium of the RSOA / SOA according to an embodiment of the present invention.

[0032] Figure 5 This is a graph showing the relationship between the reciprocal of the internal efficiency of the gain medium having / not having an n-doped active layer in a nominal optical cavity and the cavity length, according to an embodiment of the present invention.

[0033] Figure 6 This is a graph showing the relationship between mirror loss and transparent current density of a gain medium having / not having an n-doped active layer in a nominal cavity according to an embodiment of the present invention. Detailed Implementation

[0034] This invention relates to optical communication technology. One aspect of the invention provides a reflective semiconductor optical amplifier (RSOA) and / or a semiconductor optical amplifier (SOA) having a high-power gain medium for elevated temperature operation. More specifically, the invention provides an RSOA / SOA with an n-doped active layer for fabricating broadband wavelength-tunable lasers for high-speed data communication applications, although other applications are also possible.

[0035] The following description is provided to enable those skilled in the art to make and use the invention and incorporate it into a particular application context. Various modifications and uses in different applications will be apparent to those skilled in the art, and the general principles defined herein can be applied to a wide range of embodiments. Therefore, the invention is not intended to be limited to the presented embodiments, but is to be accorded the widest scope consistent with the principles and novel features of this disclosure.

[0036] In the following detailed description, numerous specific details are set forth to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without being limited to these specific details. In other instances, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring the invention.

[0037] The reader's attention is focused on all papers and documents submitted concurrently with and made publicly available with this specification, the contents of which are incorporated herein by reference. Unless otherwise expressly stated, all features disclosed in this specification (including any appended claims, abstracts, and drawings) can be replaced by alternative features for the same, equivalent, or similar purposes. Therefore, unless otherwise expressly stated, each disclosed feature is merely an example from a general series of equivalent or similar features.

[0038] Furthermore, any element in the claims that does not expressly specify the use of the terms "for a means of..." or "for a step of..." for performing a particular function shall not be construed as a "means" or "step" clause, as provided in paragraph 6 of 35 U.S.SC 112. In particular, the use of "step of..." or "action of..." in the claims herein is not intended to invoke paragraph 6 of 35 U.S.SC 112.

[0039] Please note that, if used, the markings inside, outside, left, right, front, back, top, bottom, end, forward, reverse, clockwise, and counterclockwise are for convenience only and are not intended to suggest any particular fixed direction. Rather, they are used to reflect the relative position and / or orientation between different parts of an object.

[0040] In one aspect, this disclosure provides a reflective semiconductor optical amplifier (RSOA) and / or a semiconductor optical amplifier (SOA) with high power operability at elevated temperatures. In one example, a broadband wavelength-tunable laser is formed on a silicon photonics platform using an RSOA / SOA with high power operability. Figure 1 This is a schematic diagram of a tunable laser based on a reflective semiconductor optical amplifier (RSOA) combined with a semiconductor optical amplifier (SOA) according to an embodiment of the present invention. This diagram is merely illustrative and should not unduly limit the scope of the claims. Many variations, substitutions, and modifications will be recognized by those skilled in the art. As shown, the tunable laser module 100 includes: an RSOA having a first gain medium 110 on a silicon photonic substrate 10 for generating stimulated emission; a wavelength tuner 170 formed in the silicon photonic substrate 10 and coupled to the RSOA for receiving reflected light in a broadband frequency band tuned based on stimulated emission; a wavelength locker 180 formed in the silicon photonic substrate 10 and coupled to the wavelength tuner 170 for locking the wavelength of the light; and an SOA having a second gain medium 160 in the output path coupled to the wavelength locker for single-pass power amplification of the light.

[0041] Optionally, the first gain medium 110 of the RSOA is a laser chip flip-chip bonded to a silicon photonic substrate 10. The laser chip includes an active region 115 clad along its length in a waveguide-like configuration extending through an optical cavity of length L from a back surface 101 to a front surface 102, within which stimulated emission or laser light is generated. The front surface 102 is characterized by a first reflectivity Rf, while the back surface 101 is characterized by a second reflectivity Rb. Optionally, the first reflectivity Rf is very low, for example, 0.005%, provided by an anti-reflective coating on the front surface 102. Optionally, the second reflectivity Rb is very high, for example, >90%, provided by a high-reflectivity coating on the back surface 101. Optionally, the waveguide-like active region 115 is configured with a curved shape at a non-perpendicular angle relative to the front surface 102 to reduce direct back reflection of light, but at a substantially perpendicular angle relative to the back surface 101 to maximize reflection. The laser beam is reflected by the back side 101 and emitted through the front side 102, entering the first waveguide 191 via coupler 130. Through the first waveguide 191, the laser beam is transmitted to the wavelength tuner 170. In embodiments of high-power tunable lasers, the first gain medium 110 of the RSOA is configured in the laser diode chip by design to generate a high saturation power Psat at elevated temperatures. High saturation power means the RSOA is configured to generate a high and stable laser power. However, a higher saturation power can be achieved by using a low drive current with a shorter cavity to maintain a sufficiently high gain so that it operates at a saturation power greater than 15 dBm at elevated temperatures of approximately 50°C.

[0042] refer to Figure 1After passing through wavelength tuner 170 and wavelength locker 180, the laser wavelength is locked to a specific value in a broadband spectrum (e.g., C-band) and input to the SOA via input coupler 150, where it is further power-amplified before being output via output coupler 140. Optionally, the second gain medium 160 of the SOA is another laser chip flip-chip bonded to the silicon photonic substrate 10. Gain medium 160 includes a gain region 165 clad in a cladding region of length L, configured in the form of a waveguide, extending through the amplification cavity from the back face 142 coupled to the input coupler 150 to the front face 141 coupled to the output coupler 140. In this embodiment, the front face 141 is characterized by a first reflectivity Rf, while the back face 142 is characterized by a second reflectivity Rb. Optionally, both the back surface 142 and the front surface 141 are coated with an anti-reflective coating to provide very low values, such as 0.005% for a first reflectivity Rf and a second reflectivity Rb, for forming a symmetrical semiconductor optical amplifier to allow light to pass through once and amplify the power. Optionally, the active region 165 in the form of a waveguide is configured to have a curved shape with a non-perpendicular angle relative to the back surface 142 or the front surface 141 to thereby reduce direct back reflection of light. Light received from the input coupler 150 via the back surface 142 simply passes through the cavity length L and is amplified therein before being output via the front surface 141. The second gain medium 160 of the SOA can also be designed and configured in the chip to produce a high saturation output power Psat > 15 dBm, which means a high amplified maximum output power at elevated temperatures of approximately 50°C.

[0043] Theoretically, the saturated output power Psat of the gain medium or laser diode chip can be expressed as:

[0044]

[0045] In equation (1), d is the active layer thickness of the gain medium, w is the active layer width, Γ is the optical confinement factor, a is the differential gain, and τ is the optical density. s This refers to carrier lifetime. Traditional methods have been used to improve Psat by increasing the width w of the active layer or reducing the optical confinement factor Γ (or increasing the d / Γ ratio). A drawback of reducing the confinement factor or using a wider emitter is that gain also decreases. To achieve higher gain, longer cavity lengths and higher operating currents are typically required to achieve high power. However, high operating currents are generally not recommended for devices operating at elevated temperatures.

[0046] This disclosure provides an improved SOA (or RSOA) with a high saturation power Psat for operation at elevated temperatures, offering reasonably high gain but with reduced carrier lifetime τ. sAnd differential gain a, which are achieved by providing an active layer with n-doped layers in the gain chip for SOA or RSOA. Figure 2 This is a schematic diagram of an RSOA with a gain medium according to an embodiment of the present invention, viewed from both a top and side view. This figure is merely illustrative and should not unduly limit the scope of the claims. Those skilled in the art will recognize many variations, substitutions, and modifications. As shown in part A), the top view of the RSOA gain medium 110 reveals a linear active region 115 located in an optical cavity between a front surface with an anti-reflective (AR) coating and a rear surface with a high-reflective (HR) coating. Figure 2 In part B), a cross-sectional side view of the main dielectric 110 reveals a multilayer structure, wherein the active region 115 is shown as the active layer in the central portion of the multilayer structure, sandwiched between an upper P layer and a lower N layer, forming a semiconductor diode having a p-type electrode (p-metal) on the upper P layer and an n-type electrode (n-metal) below the lower N layer. Note that the terms "upper" or "lower" are for illustrative purposes only and do not limit the actual device to only one orientation. Optionally, the P layer includes a p-type light confinement layer and a p-type cladding layer. Optionally, a contact layer exists between the P layer and the p-metal. Optionally, the N layer includes an n-type light confinement layer and an n-type cladding layer. Optionally, the N layer is formed on a substrate, and the n-metal is formed on the back side of the substrate. Optionally, the semiconductor diode is configured as a laser diode for RSOA having an optical cavity between a front and a back side.

[0047] When the laser diode is driven by a current source spanning the p-type and n-type electrodes, carriers in the active layer 115 are stimulated to emit light between the front and back sides, and then laser light is emitted from the front side. Optionally, the active layer 115 is configured as an n-type doped layer to increase carrier density and significantly reduce carrier lifetime. Optionally, the active layer 115 itself is also a multilayer structure configured to form a multiple quantum well structure. Depending on the operating wavelength spectrum, different semiconductor materials, including one or more compound semiconductors or combinations of InAsP, GaInNAs, GaInAsP, GaInAs, and AlGaInAs, can be used to form the multilayer in the active layer with the multiple quantum well structure. Optionally, the n-type dopant of the active layer 115 can be Si or Se. Optionally, the doping concentration can be 1.0 × 10⁻⁶. 18 cm -3 Up to 3.0×10 18 cm -3 Within the range.

[0048] While p-doped active layers can be used to reduce carrier lifetime, they also result in high differential gain. Therefore, p-doped active layers are not a good solution for improving RSOA Psat by reducing differential gain.

[0049] Figure 3 This is a schematic diagram of an SOA with a gain medium according to an embodiment of the present invention, viewed from both a top view and a side view. This diagram is merely illustrative and should not unduly limit the scope of the claims. Many variations, substitutions, and modifications will be recognized by those skilled in the art. In one embodiment, the gain medium of the SOA may be... Figure 2 The gain medium of the RSOA described is essentially the same. Similarly, in section A), a top view of the SOA's gain medium 160 reveals a linear active region 165 located in a cavity between a back and a front surface, both of which are coated with anti-reflective coatings. Figure 3 In part B), a cross-sectional side view of the main dielectric 160 reveals a multilayer structure, wherein the active region 165 is shown as the active layer in the central portion of the multilayer structure, sandwiched between an upper P layer and a lower N layer, forming a semiconductor diode having a p-type electrode (p-metal) on the upper P layer and an n-type electrode (n-metal) below the lower N layer. Note that the terms "upper" or "lower" are for illustrative purposes only and do not limit the actual device to only one orientation. Optionally, the P layer includes a p-type light confinement layer and a p-type cladding layer. Optionally, a contact layer exists between the P layer and the p-metal. Optionally, the N layer includes an n-type light confinement layer and an n-type cladding layer. Optionally, the N layer is formed on a substrate, and the n-metal is formed on the back side of the substrate. Optionally, the semiconductor diode is configured as a laser diode for SOA having an optical cavity between a front and a back side.

[0050] Optionally, the active layer 165 itself is a multilayer structure, configured to form a multiple quantum well structure or a heterojunction structure. Depending on the operating wavelength spectrum, different semiconductor materials, including one or more compound semiconductors or combinations of InAsP, GaInNAs, GaInAsP, GaInAs, and AlGaInAs, can be used to form the multilayer active layer with a multiple quantum well structure. Optionally, the n-type dopant of the active layer 165 can be Si or Se. Optionally, the doping concentration can be 1.0 × 10⁻⁶. 18 cm -3 Up to 3.0×10 18 cm -3 Within the range. Optionally, the active layer 165 is substantially the same as the active layer 115 in terms of its multilayer structure and the composition of each layer within the multilayer structure. Optionally, the active layer 165 and the active layer 115 are corresponding portions of two gain chips cut from the same chip in the same wafer manufactured under the same semiconductor manufacturing process.

[0051] In one embodiment, the active layer 115 of the RSOA or the active layer 165 of the SOA is a modulated n-doped multiple quantum well structure. The multiple quantum well structure of the active layer provides a heterojunction structure comprising multiple well layers separated by respective barrier layers to achieve high-power optical wave oscillation, thereby generating high saturated laser power for the RSOA or high saturated output power for the SOA relative to the bulk active layer. Figure 4 This is a simplified bandgap diagram of an n-doped active layer modulated in an RSOA / SOA gain medium according to an embodiment of the present invention. This diagram is merely illustrative and should not unduly limit the scope of the claims. Those skilled in the art will recognize many variations, substitutions, and modifications. As shown, the active layer provides a multi-layered physical stack comprising a plurality of well layers 11 separated by respective barrier layers 12. The active layer stack is located between an upper optical confinement stack and a lower optical confinement stack. The upper optical confinement stack is further attached with an upper cladding layer, and the lower optical confinement stack is further attached with a lower cladding layer. Optionally, the upper optical confinement stack plus the cladding layer is provided as a P-layer having p-type doping characteristics, such as... Figure 2 and Figure 3 As shown. Optionally, the lower light-confining stack plus the lower cladding layer is provided as an N-layer with n-type doping characteristics, such as... Figure 2 and Figure 3 As shown. Optionally, the cladding layer is selected from InP-based semiconductor materials with different doping characteristics. Reference Figure 4 The example shown includes an upper optical confinement stack comprising a barrier layer 10a and two confinement layers 21a and 22a with different thicknesses and band gaps. The lower optical confinement stack in this example also includes a barrier layer 10b and two confinement layers 21b and 22b with different thicknesses and band gaps.

[0052] In one aspect, the present invention provides a gain medium having a modulated n-doped active layer stack for generating high saturation power in semiconductor amplifiers such as RSOA and SOA. Specific material choices for the well and barrier layers, as well as parameters such as thickness and doping characteristics, vary to produce different band gaps and oscillation characteristics for the emitted light within the active layer stack, thereby providing a suitable specific spectral range, which is well-suited for applications such as RSOA or SOA in forming C-band or O-band wavelength-tunable lasers.

[0053] refer to Figure 4In the illustrated embodiment, the active layer stack consists of three well layers 11, each having a thickness t1 and a low bandgap of approximately 0.8 eV within the corresponding amplification wavelength range. For example, SOA or RSOA are used to amplify wavelengths in the C-band. Each pair of well layers is separated by a barrier layer 12 having a thickness t2 and a bandgap of approximately 0.9-1.1 eV. Optionally, there may be two well layers. Optionally, there may be four well layers. Optionally, the well thickness is approximately 4-8 nm. Optionally, the barrier thickness is approximately 5-15 nm. Optionally, the well layer 11 is selected from InGaP-based composite semiconductor materials. Optionally, the barrier layer 12 is selected from GaInAs-based composite semiconductor materials. Optionally, the active layer stack is modulated with n-type doping, such that the well layer 11 is undoped, while the barrier layer 12 is doped with n-type impurities. Optionally, the width of the n-type doped region 15 in the barrier layer 12 is not greater than the width of the barrier layer thickness t2. Optionally, the n-type doped region 15 contains Si (or Se) at a concentration ranging from 1.0 × 10⁻⁶. 18 cm -3 Up to 3.0×10 18 cm -3 And the width range is 7nm to 10nm, if the barrier layer is 10nm.

[0054] refer to Figure 4 Optionally, a barrier layer 10a (10b) is provided between the confinement layer stack and the active layer stack. Optionally, the barrier layer 10a (10b) also includes an n-doped region width, doping concentration, and band gap that are comparable to or substantially the same as those in the barrier layer 12. Optionally, the upper confinement stack includes a first p-type confinement sublayer 21a having a thickness of approximately 5-15 nm, the same as that of the barrier layer 10a, and a band gap of approximately 0.9-1.1 eV, slightly higher than that of the barrier layer 10a (similar to the approximately 0.9-1.1 eV of the active layer stack), to contain charged carriers within the active layer stack. The upper confinement stack includes a second p-type confinement sublayer 22a having a thickness of approximately 15-25 nm and a bandgap of approximately 1.1-1.2 eV higher than that of the first p-type confinement sublayer 21a, to more effectively contain charged carriers within the active layer stack for stimulated emission. Similarly, the lower confinement stack includes a first n-type confinement sublayer 21b having a thickness of approximately 5-15 nm, the same as that of the barrier layer 10b, and a bandgap of approximately 0.9-1.1 eV slightly higher than that of the barrier layer 10b (similar to an active layer stack of approximately 1 eV). Furthermore, the lower confinement stack also includes a second p-type confinement sublayer 22b having a thickness of approximately 38 nm and a bandgap of approximately 1.1-1.2 eV. Reference Figure 4The upper cladding layer has a band gap of approximately 1.3-1.4 eV, or even higher. Optionally, the upper cladding layer is InP doped with p-type dopant. The lower cladding layer also has a band gap of approximately 1.3-1.4 eV and is made of InP doped with n-type dopant.

[0055] In the embodiments, a modulated n-doped active layer stack is implemented in the gain medium for RSOA or SOA to reduce carrier lifetime without increasing differential gain, thereby achieving higher saturation power (see expression (1)). At the same time, the gain of the gain medium containing the modulated n-doped active layer stack remains high enough to enable the RSOA or SOA device to operate with a smaller cavity length at a lower injection current, thereby enabling the device to operate at elevated temperatures of 50°C or higher.

[0056] Figure 5 This is a graph illustrating the relationship between the reciprocal of the internal efficiency of a gain medium with / without an n-doped active layer in a nominal optical cavity and the cavity length, according to embodiments of the present invention. This graph is merely illustrative and should not unduly limit the scope of the claims. Those skilled in the art will recognize many variations, substitutions, and modifications. As shown, the reciprocal of the external differential quantum efficiency is plotted against the cavity length of the gain medium for a conventional undoped active layer stack (Δ) or a modulated n-doped active layer stack (O). These data were collected from cavity lengths ranging from 0.05 cm to 0.2 cm. The solid and dashed lines are linear fit lines for the two sets of data, respectively. The internal loss is calculated based on the gradient of each straight line (solid or dashed). Clearly, the modulated n-doped active layer produces lower losses compared to the undoped case (see Table 1 below). Therefore, the estimated internal losses for the gain medium with and without an n-doped active layer stack are 8.96 cm⁻¹, respectively. -1 and 6.77cm -1 This demonstrates that by modulating doping with n-type dopant in the active layer stack of the gain medium, internal efficiency can be improved to achieve higher output power.

[0057] Table 1

[0058]

[0059] Figure 6This is a graph illustrating the relationship between the mirror loss of the gain medium in a nominal optical cavity according to an embodiment of the present invention and the transparent current density. This graph is merely illustrative and should not unduly limit the scope of the claims. Those skilled in the art will recognize many variations, substitutions, and modifications. In addition to internal losses, the gain medium, when applied to a nominal optical cavity, also has mirror losses that depend on the reflectivity values ​​of its two surfaces. As shown, the mirror loss (with approximately 27% reflectivity) of the gain medium in a nominal optical cavity containing an undoped active layer stack (Δ) or a modulated n-doped active layer stack (O) is plotted relative to the logarithm of the threshold current density. The solid and dashed lines are linear fit lines for the two sets of data, respectively. The threshold gain G0 of the gain medium is calculated from the gradient of each straight line (solid or dashed), indicating that G0 ranges from 14.42 (cm²). -1 It decreased slightly to 11.12 (cm) -1 (See Table 1 above). A lower threshold gain value for the gain medium results in a lower differential gain. According to expression (1), a lower differential gain leads to a higher saturation power that the gain medium can produce, which translates to higher laser power when the gain medium is in an RSOA device and higher maximum output power when the gain medium is in an SOA device. The combination of these results in higher output power for tunable lasers based on RSOA and SOA. Figure 6 The curve shows that the transparent current density Jtr can be obtained as the current density when the cavity length is infinite or the mirror loss is zero. Table I shows that, with a gain dielectric having an undoped active layer stack, the current density is approximately 42 mA / cm². 2 In comparison, the transparent current density Jtr of the gain dielectric with n-doped active layer stacks is significantly reduced, to approximately 27 mA / cm². 2 A lower transparent current density means a lower carrier lifetime, which results in a higher saturation power, as shown in expression (1).

[0060] However, for approximately 11cm -1With a slightly lower G0, the chip gain of an RSOA or SOA device with a gain medium described in a typical 1 mm cavity length can still be at least 20 dB (at room temperature), with a nominal operating current of approximately 300 mA. This ensures a high saturation power of at least 15 dBm when the ROSA or SOA device is operated at elevated temperatures of approximately 50 °C. Sufficiently high gain can be obtained without extending the cavity length or significantly increasing the injection current, especially at elevated temperatures. Furthermore, the gain medium with modulated n-doped active layer stacks used in RSOA or SOA devices has a much higher mirror loss than typical laser devices due to the facet reflectivity setting of the gain medium cavity for a given cavity length. For an RSOA device with a gain medium in a 1 mm cavity, having an HR facet with a reflectivity >90% and an AR facet with a reflectivity of approximately 0.005%, the mirror loss is approximately 49.5 cm. -1 For an SOA device with a gain medium in a 1mm long cavity with two AR surfaces, the mirror loss is approximately 90cm². -1 Or larger.

[0061] While the foregoing is a complete description of specific embodiments, various modifications, alternative constructions, and equivalents may be used. Therefore, the foregoing description and illustrations should not be construed as limiting the scope of the invention as defined by the appended claims.

Claims

1. A semiconductor optical amplifier for high-power operation of a tunable laser (100), the semiconductor optical amplifier comprising: Gain dielectrics (110, 160) include multilayer structures with P-layers and N-layers; The front side with the first reflectivity (102, 141); and The back side has a second reflectivity (101, 142). Its features are: The first reflectivity and the second reflectivity are configured such that the gain medium generates, reflects, and amplifies at least one of laser light; and N-doped active layers (115, 165) are formed between the P layer and the N layer, and the N-doped active layers (115, 165) have undoped well layers (11) alternating with the N-doped barrier layer (15). The P-layer includes a P-type confinement layer attached to the upper portion of the N-doped active layer. The P-type confinement layer includes a first confinement sublayer (21a) having a thickness between 5 nm and 15 nm and a band gap between 0.9 eV and 1.1 eV. The upper portion of the active layer is adjacent to a barrier layer (10a) having a band gap between 0.9 eV and 1.1 eV.

2. The semiconductor optical amplifier according to claim 1, wherein: The gain medium has a length L from the front side to the back side; as well as The gain medium is based on α m =(1 / 2L)ln{1 / (Rf×Rb)} and has 40 cm -1 up to 200 cm -1 Mirror loss α between m , where Rf is the first reflectivity and Rb is the second reflectivity.

3. The semiconductor optical amplifier of claim 1, wherein the N-doped active layer is configured to provide at least 15 dBm of saturation power to the gain medium at an operating temperature up to 50°C.

4. The semiconductor optical amplifier of claim 1, wherein the N-doped barrier layer has a width between 5 nm and 15 nm and a band gap between 0.9 eV and 1.1 eV.

5. The semiconductor optical amplifier according to claim 4, wherein each of the N-doped barrier layers comprises a modulation doped region (15), and based on a barrier layer width of 10 nm, the modulation doped region (15) has a width of 1.0 × 10⁻⁶ in the range of 7 nm to 10 nm. 18 cm -3 Up to 3.0×10 18 cm -3 The range of N-type dopant concentrations.

6. The semiconductor optical amplifier of claim 1, wherein the undoped well layer has a width between 4 nm and 8 nm and a band gap of 0.8 eV.

7. The semiconductor optical amplifier according to claim 1, wherein the gain medium has a length greater than 45 cm for a length of 1 mm. -1 Up to 100cm -1 The mirror loss is reduced by the following: the front side is provided with an anti-reflective coating, the first reflectivity is less than or equal to 0.005%, the back side is provided with a reflective coating, and the second reflectivity is greater than 90%.

8. The semiconductor optical amplifier of claim 7, wherein the N-doped active layer is configured as a linear waveguide through the optical cavity of the gain medium, and wherein the linear waveguide forms a non-perpendicular angle with respect to the front side and a perpendicular angle with respect to the back side.

9. The semiconductor optical amplifier according to claim 1, wherein the gain medium has a length greater than 90 cm for a length of 1 mm. -1 Up to 200cm -1 The mirror loss is reduced by the anti-reflective coating on the front side, the first reflectivity being less than or equal to 0.005%, and the anti-reflective coating on the back side, the second reflectivity being less than or equal to 0.005%, to form a symmetrical semiconductor optical amplifier.

10. The semiconductor optical amplifier of claim 9, wherein the gain medium is configured as an optical cavity for amplifying laser light in the N-doped active layer, and wherein the laser light is input once through the back side and emitted through the front side.

11. The semiconductor optical amplifier of claim 10, wherein the N-doped active layer is configured as a linear waveguide through the optical cavity of the gain medium, and wherein the linear waveguide forms a non-perpendicular angle with respect to the front side and a non-perpendicular angle with respect to the back side.

12. The semiconductor optical amplifier of claim 1, wherein the P layer further comprises a P-type cladding layer, the P-type cladding layer being attached to the side of the P-type confinement layer further away from the N-doped active layer than the P-type confinement layer.

13. The semiconductor optical amplifier of claim 12, wherein the P-type confinement layer further comprises: The second confinement sublayer (22a), having a thickness between 15 nm and 25 nm and a band gap between 1.1 eV and 1.2 eV, is attached to the side of the first confinement sublayer that is further away from the N-doped active layer than the first confinement sublayer.

14. The semiconductor optical amplifier of claim 1, wherein the N-layer comprises an N-type confinement layer and an N-type cladding layer, the N-type confinement layer being attached to the lower portion of the N-doped active layer, and the N-type cladding layer being attached to the side of the N-type confinement layer further away from the N-doped active layer than the N-type confinement layer.

15. The semiconductor optical amplifier of claim 14, wherein the N-type confinement layer comprises: (i) a first confinement sublayer (21b) having a thickness between 5 nm and 15 nm and a band gap between 0.9 eV and 1.1 eV, wherein the lower portion of the N-doped active layer is attached to a barrier layer (10b) having a band gap between 0.9 eV and 1.1 eV; and (ii) a second confinement sublayer (22b) having a thickness between 15 nm and 80 nm and a band gap between 1.1 eV and 1.2 eV, attached to the side of the first confinement sublayer further away from the N-doped active layer than the first confinement sublayer.

16. The semiconductor optical amplifier of claim 1, wherein the gain medium i) extends from the front side to the back side; ii) has a mirror loss for amplifying data communication; and iii) includes the multilayer structure.

17. The semiconductor optical amplifier of claim 1, wherein the front side is configured to receive laser light from a laser.

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