High-speed modulated laser

Abstract

A modulated laser is described, comprising a laser (30) optically coupled to a modulator (50), the modulator (50) having an intrinsic region (52) comprising: a multi-quantum-well material (41); a field control layer (42) having a doping density to enhance the electric field in the multi-quantum-well material; and a collection layer (43) having a band gap higher than that of the multi-quantum-well material (41). Combining the field control layer and the collection layer in the intrinsic region of the modulator of the modulated laser eliminates the need for a trade-off between high speed and low external bias in the modulated laser.

Description

Technical Field

[0001] This invention relates to lasers, and for example to improving the speed of modulated lasers. Background Technology

[0002] In externally modulated lasers (MLs), a trade-off may need to be struck between high speed and low bias requirements.

[0003] The standard approach to this problem is to use a PIN structure, in which an intrinsic layer of semiconductor material is sandwiched between p-type and n-type semiconductor layers in the modulator. To meet high-speed requirements, the modulator should have low capacitance. This means that, for a standard PIN structure, the intrinsic region should be relatively thick.

[0004] However, a greater intrinsic thickness means a weaker electric field across the intrinsic region. Therefore, for a given external bias, the modulator may have a lower extinction ratio.

[0005] Figures 1(a) and 1(b) schematically illustrate a top and side view, respectively, of a standard ML comprising a distributed feedback (DFB) laser section 10 and a Mach-Zehnder (MZ) modulator section 21. The DFB and MZ sections are typically optically coupled using a docking coupling method, with an isolation zone between them. The device has a rear surface 13 into which light enters and a front surface 14 into which light is emitted. The rear surface 13 may be coated with a high-reflection (HR) coating, and the front surface 14 may be coated with an anti-reflection (AR) coating. Electrical bias can be applied to portions of the device via electrodes 20a, 20b, and 20c.

[0006] The multiple quantum well (MQW) material 19 of the MZ intrinsic region (MQW2) is grown in a docking coupling with the MQW material 16 of the DFB intrinsic region (MQW1). In this example, the MQW1 layer 16 has a p-type semiconductor layer 15 above it and an n-type semiconductor layer 17 below it. The MQW2 layer 19 has a p-type semiconductor layer 18 above it and an n-type semiconductor layer 17 below it. Deep etching between the DFB and MZ portions is used to achieve electrical isolation.

[0007] A multi-mode interferometer (MMI) 22 splits the light input to the two arms of modulators 21a and 21b. A second MMI 24 recombines the light from the two arms. The MQW material 19 of the Mach-Zehnder modulator (MQW2) is dock-coupled with the MQW material 16 of the DFB (MQW1). The laser can also be a tunable DBR laser. The laser and the Mach-Zehnder modulator can be monolithically integrated or optically coupled. The MMI core guiding the light can have the same composition as the MQW2 region, or it can include a separate overgrowth material.

[0008] Figure 1(c) shows the electric field distribution in region 19 of the modulator in MQW2. The electric field is higher than that in the n-type and p-type layers on either side of the intrinsic region and is approximately constant. The bandwidth of the modulator is also primarily determined by the capacitance of the PIN structure.

[0009] For reliable laser mechanics (ML), the fabrication and growth conditions of the docking coupling are crucial. To improve output power, DFBs are typically coated with high-performance organic flux (HR). The waveguide of a DFB is usually designed to have only the fundamental mode and typically has a uniform width, although this can vary depending on the laser design. The field in the modulator's intrinsic region is approximately constant.

[0010] In conventional electroabsorption modulated lasers (EMLs), a trade-off must also be made between the bandwidth on the electroabsorption modulator (EAM) and the applied external bias, because both the bandwidth and electric field in the intrinsic region depend on the thickness of the PIN intrinsic region.

[0011] The goal is to develop a modulated laser with improved performance. Summary of the Invention

[0012] According to one aspect, a modulated laser is provided, comprising a laser optically coupled to a modulator, the modulator having an intrinsic region comprising: a multi-quantum-well material; a field control layer having a doping density to enhance the electric field in the multi-quantum-well material; and a collection layer having a band gap higher than that of the multi-quantum-well material.

[0013] The modulated laser can be an externally modulated laser. The modulator can modulate the light emitted by the laser. The modulator can have a PIN structure or a NIP structure. This structure includes an intrinsic region between a p-type semiconductor material layer and an n-type semiconductor material layer. This structure can be easily fabricated using semiconductor deposition and / or growth techniques.

[0014] The intrinsic region can be made of semiconductor materials, including but not limited to InP, InGaAsP, InGaAlAs, InGaAlAsSb, GaAs, AlGaAs, GaN, AlGaN, Ge, or Si. Therefore, this structure is compatible with a range of semiconductor materials, which can be selected depending on the application of the modulated laser.

[0015] The laser can be a distributed feedback laser, a distributed Bragg reflector laser, or a tunable laser. Therefore, the device can be tuned according to its desired application. The modulated laser can also have a semiconductor optical amplifier (SOA) optically coupled to the modulator. The SOA can receive the light emitted by the modulator. The phase component can also be optically coupled to both the laser and the modulator.

[0016] The modulator can be a Mach-Zehnder modulator or an electroabsorption modulator. This type of modulator is commonly used in telecommunications applications.

[0017] Voltages can be applied to electrodes or contacts on opposite top and bottom sides of the device section to control the laser and modulator sections. This allows different parts of the modulated laser to be controlled independently. When the modulator is a Mach-Zehnder modulator, the electrodes can be lumped electrodes, traveling-wave electrodes, or segmented traveling-wave electrodes with capacitive loads. When the modulator is an electroabsorption modulator, the electrodes can be lumped electrodes or traveling-wave electrodes.

[0018] The modulator can be a Mach-Zehnder modulator, and the modulated laser can also include a beam splitter. This allows the light leaving the laser to be optically split into two waveguide interferometer arms. If a voltage is applied to one arm of the Mach-Zehnder modulator, the light passing through that arm will experience a phase shift. When the light from each of the two arms is recombined, the phase difference is converted into amplitude modulation.

[0019] The doping density of the collection layer can be 1.0e15 / cm. 3 With 8e17 / cm 3 Between these two points, the behavior of the collector layer can be controlled. The doping density can depend on the thickness of the collector layer. The introduction of the collector layer can reduce the overall capacitance of the structure. At the same time, it can also allow charge carriers (mainly electrons) to move to the n-side of the PIN structure.

[0020] The collection layer can be p-doped or n-doped. This allows for the versatility of the modulator structure.

[0021] The band gap of the collection layer can be constant or stepped. A constant band gap makes the layer easier to manufacture.

[0022] The thickness of the collection layer can be between 20 nm and 1000 nm. The thickness of the field control layer can be between 10 nm and 500 nm.

[0023] Field control layers can have higher band gaps than multi-quantum-well materials. The doping density of field control layers can reach 1e17 / cm². 3 With 1e19 / cm 3 The spacing between these elements ensures that it does not introduce additional absorption and allows for a larger electric field to pass through the MQW material.

[0024] When the modulator is an electroabsorption modulator, charge can be primarily carried by electrons in the collector layer. Under EAM modulator operation, the EAM absorbs the incident light. Therefore, charge carriers are generated in the intrinsic region of the MQW material: electrons in the conduction band and holes in the valence band. Under reverse bias, the holes move to the p-InP side, similar to a conventional PIN structure. Electrons move to both the collector layer and the n-InP layer. Therefore, in the collector layer, electrons are the effective charge carriers.

[0025] The modulator may include a front surface that is the emitting surface of the modulated laser, and the front surface is coated with an anti-reflective coating. The anti-reflective coating prevents reflection of light exiting the device at the front surface. This can improve the efficiency of the modulated laser.

[0026] Lasers can include a back reflector coated with a highly reflective coating. This can increase power and improve laser efficiency. The back reflector can be a rear end facet, while the front facet can be a front end facet. Both the front and rear end facest can be cleaved surfaces. This is a convenient method for manufacturing modulated lasers. The back reflector and front facet can also be formed using other convenient methods.

[0027] Modulated lasers can include waveguides for guiding light along the device; these waveguides can be ridge waveguides or embedded heterostructure waveguides. This allows for versatility in device structure.

[0028] Modulated lasers can be integrated with other optical functional structures and can be used in a variety of applications, such as telecommunications systems. Attached Figure Description

[0029] The invention will now be described by way of example with reference to the accompanying drawings.

[0030] In the attached diagram:

[0031] Figure 1(a) and 1(b) Top and side views of a standard ML laser, including optical coupling to a Mach-Zehnder modulator, are shown respectively.

[0032] Figure 1(c) shows the structure and electric field distribution of the intrinsic region of a standard ML with a Mach-Zehnder modulator (along the BB section of Figure 1(b)).

[0033] Figure 2(a) and 2(b) Top and side views of an embodiment of an ML optically coupled to a Mach-Zehnder modulator are shown, respectively.

[0034] Figure 3(a) schematically illustrates an example of the structure of the intrinsic region of a Mach-Zehnder modulator.

[0035] Figure 3(b) shows the electric field distribution in the intrinsic region shown in Figure 3(a). Detailed Implementation

[0036] like Figure 2(a) and 2(b) As shown, one example of the ML described herein includes a DFB laser optically coupled to a Mach-Zehnder modulator. In this example, the device has a PIN structure with a p-doped semiconductor layer above and an n-doped semiconductor layer below. However, the device could also have a NIP structure with an n-doped semiconductor layer above and a p-doped semiconductor layer below.

[0037] As shown in Figures 2(a) and 2(b), the DFB laser 30 typically includes a semiconductor block having a rear surface or rear end face 33 of ML at one end. The DFB laser has an intrinsic region comprising MQW material (MQW3) 35. A side view along CC is shown in Figure 2(b).

[0038] The intrinsic region 35 has a p-InP semiconductor layer 36 above it and an n-InP semiconductor layer 37 below it. Therefore, in this example, the laser has a PIN structure. The laser can also have a NIP structure, with an n-doped semiconductor layer above it and a p-doped semiconductor layer below it.

[0039] The device uses a multi-mode interferometer (MMI) 51 or other beam splitter to split the light leaving the DFB laser 30 into two waveguide interferometer arms 50a and 50b. If a voltage 50 is applied to one arm of the Mach-Zehnder modulator, the light passing through that arm will undergo a phase shift. When the light from each of the two arms is recombined, the phase difference is converted into amplitude modulation.

[0040] Modulator 50 has an intrinsic region, as shown in 52 (MQW FCL). In this example, the intrinsic region of the modulator has a p-InP semiconductor layer 39 above it and an n-InP semiconductor layer 37 below it, i.e., the modulator has a PIN structure. Alternatively, the modulator may have a NIP structure. The composition of intrinsic region 52 is shown in Figure 3(a).

[0041] The intrinsic region 52 of the Mach-Zehnder modulator between the p-doped layer 39 and the n-doped layer 37 includes an MQW (or bulk) material 41, a field control layer (FCL) 42, and a collection layer 43, as shown in Figure 3(a).

[0042] The field control layer 42 has a doping density to enhance the electric field in the multi-quantum-well material. The field control layer is typically doped so that the electric field is primarily concentrated in the intrinsic MQW (i-MQW) region 41. Therefore, the electric field in the MQW material is increased relative to the conventional intrinsic region. The doping density can depend on the thickness of the intrinsic MQW region and the desired electric field. The thickness of the field control layer can be between 10 nm and 500 nm, and the doping density can be 1e17 / cm². 3 With 1e19 / cm 3 The specific values ​​vary depending on the modulator structure. The field control layer can be readily p-doped for NIP structures or n-doped for PIN structures. The field control layer 42 preferably has a higher bandgap energy than the multi-quantum-well material 41. The field control layer generates a higher electric field in the depletion absorption layer than in a conventional depletion layer.

[0043] The collector layer 43 preferably has a higher band gap than the multi-quantum-well material to avoid additional absorption. The collector layer may be undoped or have a low doping concentration (lower than the doping concentration of the collector layer). The band gap energy of the collector layer may be constant for ease of fabrication or may be graded. The collector layer may be p-doped or n-doped, depending on the structure. The collector layer is formed from a high-bandgap material with low or no doping, resulting in a lower overall capacitance of the modulator, which is detrimental to additional absorption. In the collector layer, charge is primarily carried by electrons. Since only electrons are effective charge carriers, a fast electron transit time can be utilized. The collector layer is used to reduce the capacitance of the modulator.

[0044] Therefore, the introduction of the collection layer can reduce the total capacitance of the modulated laser structure. Simultaneously, it allows charge carriers (mainly electrons) to move to the n-side of the PIN structure.

[0045] In the case of ML including Mach-Zehnder modulators, the collection layer can have the same or greater bandgap energy as the intrinsic MQW material. Figure 3(b) shows the electric field distribution in the MQW FCL region shown in Figure 3(a) (i.e., along the DD section in Figure 2(b)).

[0046] The light passing through each arm 50a, 50b of the Mach-Zehnder modulator 50 is recombined at the second MMI 53 and then emitted from the modulated laser at the front surface 34.

[0047] Therefore, the modulator typically includes a first semiconductor layer of a first doping type, a second semiconductor layer of a second doping type opposite to the first type, and an intrinsic region. The material forming the device can be selectively doped in regions of the p-type and n-type layers. The first and second semiconductor layers, as well as the intrinsic region, extend in a direction extending between the rear surface 33 and the front surface 34 of the device.

[0048] The length of the ML device is defined between the rear surface or rear end face 33 and the front surface or front end face 34. The rear end face with an HR coating serves as a rear reflector. Preferably, the front end face and the rear end face are aligned parallel to each other. Preferably, the front end face is orthogonal to the length of the device. Preferably, the rear end face is orthogonal to the length of the device. One or more front and / or rear surfaces of the device can be formed by splitting. The width of the waveguide in the laser and modulator portions is preferably perpendicular to the length of the device, and the waveguide preferably guides light in a direction along the length of the ML device. Semiconductor layers 35, 36, 37, 39, and 52 extend in a direction extending between the rear surface 33 and the front surface 34.

[0049] Voltages can be applied to electrodes or contacts 40a, 40b, and 40c on opposite top and bottom sides of the cavity to control the laser and modulator sections of the device. This allows different parts of the ML to be controlled independently.

[0050] Light exits the device from the waveguide at point 34 on the front surface; that is, the front surface is the emitting surface of ML.

[0051] In the above arrangement, the modulator is a Mach-Zehnder modulator. In another embodiment, the modulator of the ML can be an electroabsorption modulator (EAM).

[0052] When the modulator is a Mach-Zehnder modulator, the electrodes can be lumped electrodes, traveling-wave electrodes, or segmented traveling-wave electrodes with a capacitive load. When the modulator is an electroabsorption modulator, the electrodes can be lumped electrodes or traveling-wave electrodes.

[0053] Due to the field control layer, the change in electric field in the modulator's MQW material causes a change in the refractive index of the aforementioned MZ modulator, or a change in absorption of the modulator including the EAM under reverse bias.

[0054] In the example above, the laser is a DFB laser. However, the laser can be any other convenient type of laser, such as a distributed Bragg reflector laser or a tunable laser.

[0055] In embodiments of the present invention, the semiconductor may be InP, InGaAsP, InGaAlAs, InGaAlAsSb, GaAs, AlGaAs, GaN, AlGaN, Ge, Si, or other suitable semiconductor materials. The semiconductor material may be selected based on the application of the modulated laser.

[0056] As described above, the intrinsic region of the modulator includes the MQW material, the field control layer, and the collection layer. Combining the field control layer and the collection layer within the intrinsic region of the modulator eliminates the need for a trade-off between high speed and low external bias in the modulated laser. In such a modulated laser, high-speed operation and low external bias can be achieved simultaneously.

[0057] Due to the field control layer, the electric field in the i-MQW region is stronger than that of standard EAM or Mach-Zehnder modulators. Therefore, the modulator requires a lower external bias. The total capacitance of the modulator is also lower than that of conventional devices due to the presence of the collection layer. This enables higher speeds, greater bandwidth, and better power handling.

[0058] Therefore, the modulated laser described in this paper may require a lower external bias during operation, which could reduce power consumption. The proposed modulated laser can have a larger bandwidth without compromising the bias voltage.

[0059] The proposed device is particularly well-suited for high-speed operation and may offer better linear frequency modulation and power handling.

[0060] The applicant hereby discloses each individual feature described herein, as well as any combination of two or more such features. With ordinary knowledge of those skilled in the art, such features or combinations can be implemented as a whole according to this specification, regardless of whether such features or combinations of features solve any problem disclosed herein; and without limiting the scope of the claims. The applicant notes that aspects of the invention may include any such individual feature or combination of features. In view of the foregoing description, those skilled in the art will appreciate that various modifications can be made within the scope of the invention.

Claims

1. A modulated laser, characterized in that, A laser (30) including an optically coupled modulator (50) having an intrinsic region (52) comprising: Multi-quantum-well materials (41); A field control layer (42) having a doping density to enhance the electric field in the multi-quantum well material; in the case that the modulated laser includes a Mach-Zehnder modulator, the field control layer (42) has a higher band gap than the multi-quantum well material (41); The collection layer (43) has a higher band gap than the multi-quantum well material (41), the collection layer (43) is undoped or has a low doping concentration, and the band gap of the collection layer (43) is constant.

2. The modulated laser according to claim 1, characterized in that, The modulator (50) has a PIN or NIP structure.

3. The modulated laser according to claim 1, characterized in that, The intrinsic region (52) is made of at least one of InP, InGaAsP, InGaAlAs, InGaAlAsSb, GaAs, AlGaAs, GaN, AlGaN, Ge and Si.

4. The modulated laser according to any one of claims 1 to 3, characterized in that, The laser (30) is a distributed feedback laser, a distributed Bragg reflection laser, or a tunable laser.

5. The modulated laser according to claim 4, characterized in that, In the collection layer, the charge is mainly carried by electrons.

6. The modulated laser according to any one of claims 1 to 3, characterized in that, The doping density of the collection layer (43) is 1.0e15 / cm. 3 With 8e17 / cm 3 between.

7. The modulated laser according to any one of claims 1 to 3, characterized in that, The collection layer (43) is p-doped or n-doped.

8. The modulated laser according to any one of claims 1 to 3, characterized in that, The thickness of the collection layer (43) is between 20 nm and 1000 nm.

9. The modulated laser according to any one of claims 1 to 3, characterized in that, The modulator includes a front surface (34), which is the emitting surface of the modulated laser, and the front surface is coated with an anti-reflective coating.

10. The modulated laser according to any one of claims 1 to 3, characterized in that, The thickness of the field control layer (42) is between 10 nm and 500 nm.

11. The modulated laser according to any one of claims 1 to 3, characterized in that, The doping density of the field control layer (42) is 1e17 / cm. 3 With 1e19 / cm 3 between.

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