Semiconductor-based modulator including conductive tape

Abstract

The electro-optical modulator may include a radio frequency (RF) modulation region including a first optical waveguide, a second optical waveguide, a first set of electrode segments, a second set of electrode segments, and a conductive band. The first optical waveguide may propagate a first optical signal. The second optical waveguide may propagate a second optical signal. The first set of electrode segments may apply a first RF signal to the first optical waveguide. The second set of electrode segments may apply a second RF signal to the second optical waveguide. The conductive band may enable extraction from the electro-optical modulator of a light current generated in the first and second optical waveguides and flowing through a doped layer below the first and second optical waveguides. The conductive strip may be in ohmic contact with the doped layer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 510,768, entitled “Semiconductor-Based Modulator Including Conductive Elements,” filed on June 28, 2023. The disclosure of that prior application is considered part of and incorporated by reference into this patent application. Technical Field

[0003] The present disclosure generally relates to a semiconductor-based modulator and a semiconductor-based modulator including a conductive strip. Background Art

[0004] An electro-optic modulator is a device that applies an electrical signal (such as a radio frequency (RF) signal) to an optical signal to generate a modulated optical signal (e.g., an optical signal modulated to carry data represented by the electrical signal). An electro-optic modulator may include a traveling wave electrode structure positioned adjacent to an optical waveguide. In operation, the electric field generated by the electrode structure overlaps (e.g., a predetermined distance) with the optical waveguide within the modulation region and causes electromagnetic interaction to generate a modulated optical signal. For example, the electro-optic modulator may take the form of a Mach-Zehnder (MZ) interferometer including an RF waveguide, wherein the RF waveguide includes two tracks, each of which is electrically connected to a set of RF electrode segments, wherein each set of RF electrode segments is arranged on one of the two optical waveguides. Here, the RF signal applied to the optical waveguide by the RF electrode group is used to modulate the optical signal propagating in the optical waveguide. Summary of the invention

[0005] In some embodiments, the electro-optic modulator includes: an RF modulation region, the RF modulation region including: a first optical waveguide, the first optical waveguide being used to propagate a first optical signal traveling in a propagation direction; a second optical waveguide, the second optical waveguide being used to propagate a second optical signal traveling in the propagation direction; a first group of electrode segments, the first group of electrode segments being used to apply a first RF signal to the first optical waveguide in association with modulating the first optical signal, the first RF signal being provided by a first track of the RF waveguide and traveling in the propagation direction; a second group of electrode segments, the second group of electrode segments being used to apply a second RF signal to the second optical waveguide in association with modulating the second optical signal, the second RF signal being provided by a second track of the RF waveguide and traveling in the propagation direction; and a conductive strip, the conductive strip being used to enable extraction of photocurrent generated in the first optical waveguide and the second optical waveguide and flowing through a doped layer below the first optical waveguide and the second optical waveguide from the electro-optic modulator, the conductive strip being between the first optical waveguide and the second optical waveguide and in ohmic contact with the doped layer.

[0006] In some embodiments, the conductive strip provides a lower impedance conductive path for the photocurrent than a conductive path provided by the doped layer.

[0007] In some embodiments, the conductive strip is not directly connected to an external bias connection of the electro-optic modulator.

[0008] In some embodiments, the conductive tape includes an ohmic contact layer and a cover layer.

[0009] In some embodiments, the length of the conductive tape is greater than or equal to the total length of the first set of electrode segments and the total length of the second set of electrode segments.

[0010] In some embodiments, ends of the conductive tape extend beyond ends of the first set of electrode segments and ends of the second set of electrode segments.

[0011] In some embodiments, the conductive tape comprises a single conductive segment.

[0012] In some embodiments, the conductive strip includes at least two conductive segments.

[0013] In some embodiments, the conductive strap contacts the doped layer through an opening in a dielectric layer above the doped layer.

[0014] In some embodiments, the electro-optic modulator is a III-V semiconductor modulator.

[0015] In some embodiments, the electro-optic modulator includes: a substrate; a first doped layer above the substrate; an undoped layer above the first doped layer; a second layer above the undoped layer, wherein a first region of the first doped layer, a first region of the undoped layer, a first region of the second layer, and a first portion of the dielectric layer form a first rib structure, and wherein the second region of the first doped layer, the second region of the undoped layer, the second region of the second layer, and the second portion of the dielectric layer form a second rib structure; a first group of electrode segments, the first group of electrode segments are above the first rib structure; a second group of electrode segments, the second group of electrode segments are above the second rib structure; a first track of an RF waveguide, the first track being electrically connected to the first group of electrode segments; a second track of the RF waveguide, the second track being electrically connected to the second group of electrode segments; and a conductive band, the conductive band being in ohmic contact with a third region of the first doped layer, the third region of the first doped layer being between the first region of the first doped layer and the second region of the first doped layer.

[0016] In some embodiments, the conductive strip is used to enable extraction from the electro-optic modulator of a photocurrent generated in the rib-like structure and the second rib-like structure and flowing through the first doped layer.

[0017] In some embodiments, the conductive strip is not directly connected to an external bias connection of the electro-optic modulator.

[0018] In some embodiments, the conductive tape includes an ohmic contact layer and a capping layer over the ohmic contact layer.

[0019] In some embodiments, the conductive tape comprises a single conductive segment.

[0020] In some embodiments, the conductive strap contacts the doped layer through an opening in a dielectric layer above the doped layer.

[0021] In some embodiments, the electro-optic modulator is a III-V semiconductor modulator.

[0022] In some embodiments, a semiconductor-based modulator includes: an RF modulation region, the RF modulation region including: a first optical waveguide, the first optical waveguide being used to propagate a first optical signal traveling in a propagation direction; a second optical waveguide, the second optical waveguide being used to propagate a second optical signal traveling in the propagation direction; an RF waveguide, the RF waveguide being used to apply a first RF signal to the first optical waveguide and a second RF signal to the second optical waveguide, the first RF signal and the second RF signal traveling in the propagation direction; and a conductive strip, the conductive strip being used to reduce the impedance on a conductive path between an external bias connection of the semiconductor-based modulator and doped regions beneath the first optical waveguide and the second optical waveguide, so as to enable extraction of photocurrent flowing through the doped regions from the semiconductor-based modulator.

[0023] In some embodiments, the conductive band is in ohmic contact with the doped region.

[0024] In some embodiments, the conductive strap is not directly connected to the external bias connection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1A-1B is a schematic diagram of an example implementation of a semiconductor-based modulator including a conductive strip.

[0026] Figure 2A-2B is a schematic diagram illustrating the difference between an equivalent circuit of a conventional semiconductor-based modulator and an equivalent circuit of a semiconductor-based modulator including a conductive strip as described herein.

[0027] Figure 3A-3Bis a schematic diagram illustrating example measurement results showing the improved performance of semiconductor-based modulators with conductive strips described herein compared to conventional semiconductor-based electro-optic modulators. DETAILED DESCRIPTION

[0028] The following detailed description of example embodiments refers to the accompanying drawings.The same reference numbers in different drawings may identify the same or similar elements.

[0029] Semiconductor-based electro-optic modulators (such as indium phosphide (InP)-based MZ modulators) are DC biased during operation. During operation, some light is absorbed in the optical waveguides of the semiconductor-based electro-optic modulator. This absorption generates a photocurrent. In conventional semiconductor-based electro-optic modulators, the longitudinal sheet impedance in the doped layer between the optical waveguides is significant, and therefore, the photocurrent induced in each modulation segment induces a voltage drop across this impedance. This voltage drop reduces the bias applied to the portion of the modulation region of the semiconductor-based electro-optic modulator. The magnitude of the bias reduction increases with increasing distance from the bias electrode, wherein a greater bias reduction is seen farther from the bias electrode. This bias reduction reduces the electro-optic efficiency in the affected portion of the semiconductor-based electro-optic modulator, which results in an increase in the switching voltage. In particular, because the amount of photocurrent generated depends on the optical power, the increase in the switching voltage depends on the optical input power, and therefore depends on the current applied to the pre-modulator semiconductor optical amplifier (SOA) (e.g., the SOA upstream of the semiconductor-based electro-optic modulator). The dependence of the switch voltage on the pre-modulator SOA current increases the setup complexity. For example, an increase in the pre-modulator SOA current will require an increase in the bias voltage (e.g., to cope with the increased switch voltage), and therefore, different configurations will be required for different pre-modulator SOA current levels.

[0030] Some embodiments described herein provide a semiconductor-based electro-optic modulator comprising a conductive strip. In some embodiments, the semiconductor-based electro-optic modulator comprises a first optical waveguide for propagating a first optical signal traveling in a propagation direction, and a second optical waveguide for propagating a second optical signal traveling in the propagation direction. The semiconductor-based electro-optic modulator further comprises a first set of electrode segments for applying a first RF signal to the first optical waveguide, wherein the first RF signal is provided by a first track of the RF waveguide and travels in the propagation direction, and comprises a second set of electrode segments for applying a second RF signal to the second optical waveguide, wherein the second RF signal is provided by a second track of the RF waveguide and travels in the propagation direction. The semiconductor-based electro-optic modulator further comprises a conductive strip between the first optical waveguide and the second optical waveguide. The conductive strip is in ohmic contact with a doped layer below the first optical waveguide and the second optical waveguide. The conductive strip enables the photocurrent generated in the first optical waveguide and the second optical waveguide and flowing through the doped layer to be extracted from the electro-optic modulator. In some embodiments, the conductive strip reduces longitudinal impedance and thus reduces or eliminates de-biasing effects, such that the modulation region of the semiconductor-based electro-optic modulator is subject to substantially the same bias conditions regardless of the photocurrent level. As a result, the switching voltage of the semiconductor-based electro-optic modulator is reduced (e.g., at a given pre-modulator SOA current level), and further, the dependence of the switching voltage on optical power is reduced or eliminated. In this way, electro-optical efficiency is improved while reducing setup complexity. Additional details are provided below.

[0031] Figure 1A-1B is a schematic diagram of an example implementation of a semiconductor-based electro-optic modulator 100 (referred to herein as modulator 100 ) including a conductive strip. Figure 1A The modulator 100 is Figure 1B A schematic diagram of an example cross section at the dashed line labeled "xx" in the example plan view shown.

[0032] As shown, the modulator 100 includes a substrate 102. The substrate 102 is a supporting material on or in which one or more layers or features of the modulator 100 are grown or fabricated. In some embodiments, the substrate 102 includes a semi-insulating type of material. A semi-insulating substrate is a type of semiconductor substrate that has been heavily doped with, for example, chromium or iron to act as a trap for electrons and holes, which makes the semiconductor substrate "semi-insulating". The modulator 100 including the conductive strip 122 can be made in practice on a substrate 102 including semi-insulating InP, semi-insulating gallium arsenide (GaAs), or another semi-insulating type III-V semiconductor material in order to reduce losses (for example, because the RF waveguide 116 needs to be on an insulating substrate to keep losses low). This is why it is necessary to extract current along the conductive strip 122 - current cannot be extracted through the (semi-insulating) substrate 102. Therefore, in practice, the substrate 102 can be a semi-insulating III-V semiconductor substrate corresponding to the III-V material of the modulator 100 itself. Therefore, in some embodiments, the modulator 100 can be referred to as a III-V semiconductor modulator.

[0033] As also shown, the modulator 100 includes a first doped layer 104, an undoped layer 106, a second layer 108, and a dielectric layer 110. The first doped layer 104 includes a doped semiconductor material. In some embodiments, the second layer 108 includes an oppositely doped semiconductor material. That is, in some embodiments, the second layer 108 can be a second doped layer, wherein the doping of the second layer 108 is opposite to the doping of the first doped layer 104. Alternatively, in some embodiments, the second layer 108 can include a material having the same type of doping as the first doped layer 104. In one example, the first doped layer 104 and the second layer 108 can be an n-doped layer for forming an npin diode in which p-type material is minimized. Alternatively, in some embodiments, the second layer 108 can include an unintentionally doped material. As an example, the second layer 108 in a GaAs traveling wave modulator can have no doping, and a Schottky (e.g., metal to undoped semiconductor) contact can be used to apply an RF signal. In some embodiments, the undoped layer 106 includes an intrinsic (i.e., undoped) semiconductor material.

[0034] The first region of the first doped layer 104, the first region of the undoped layer 106, the first region of the second layer 108, and the first portion of the dielectric layer 110 (e.g., the portion of the dielectric layer 110 on the sidewalls of the first region of the first doped layer 104, the first region of the undoped layer 106, and the first region of the second layer 108) form a first rib structure 112a, such as Figure 1A. The first rib structure 112a defines a first optical waveguide of the modulator 100. Similarly, the second region of the first doped layer 104, the second region of the undoped layer 106, the second region of the second layer 108, and the second portion of the dielectric layer 110 (e.g., the portion of the dielectric layer 110 on the sidewalls of the second region of the first doped layer 104, the second region of the undoped layer 106, and the second region of the second layer 108) form a second rib structure 112b, as shown in FIG. Figure 1A The second rib structure 112b defines a second optical waveguide of the modulator 100. In some embodiments, the first rib structure 112a and the second rib structure 112b extend along the modulation region 114 of the modulator 100, as shown in FIG. Figure 1B As shown. The modulation region 114 is a region of the modulator 100 in which an RF signal can be applied to the first and second optical waveguides of the modulator 100 in association with a modulated input optical signal (e.g., a continuous wave light to be modulated when the continuous wave light passes through the modulator 100), as described below. In one example, the first doped layer 104 is an n-doped layer and the second layer 108 is a p-doped layer. In such an embodiment, a region of the first doped layer 104, a region of the undoped layer 106, a region of the second layer 108, and a portion of the dielectric layer 110 form rib structures 112a and 112b, and the rib structures 112a and 112b include pin junctions along their respective lengths in the modulation region 114. As another example, in some embodiments, the first doped layer 104 can be a p-doped layer and the second layer 108 can be an n-doped layer. In such an embodiment, a region of the first doped layer 104, a region of the undoped layer 106, a region of the second layer 108, and a portion of the dielectric layer 110 form rib-like structures 112a and 112b, and the rib-like structures 112a and 112b include nip junctions along their respective lengths in the modulation region 114. As another example, the first doped layer 104 is an n-doped layer and the second layer 108 is an n-doped layer. In such an embodiment, a region of the first doped layer 104, a region of the undoped layer 106, a region of the second layer 108, a minimum amount of p-type material between the undoped layer 106 and the second layer 108, and a portion of the dielectric layer 110 form rib-like structures 112a and 112b, and the rib-like structures 112a and 112b include npin junctions along their respective lengths in the modulation region 114.

[0035] As also shown, the electro-optic modulator 100 includes an RF waveguide 116, which includes a first track 118a and a second track 118b. The first track 118a is electrically connected (e.g., through a first set of air bridges) to a first set of RF electrode segments 120a above a first rib-like structure 112a (i.e., a first optical waveguide). The second track 118b is electrically connected (e.g., through a second set of air bridges) to a second set of RF electrode segments 120b above a second rib-like structure 112b (i.e., a second optical waveguide). Figure 1B As shown, a given set of RF electrode segments 120 may include one or more modulation segments (e.g., at least two separate RF electrode segments). Figure 1A-1B As shown, the RF waveguide 116 may be in the form of an RF coplanar stripline (CPS) waveguide. It is worth noting that Figure 1A and Figure 1B The RF waveguide 116 shown in FIG. 1 is provided as an example, and other types of RF waveguides may be used. For example, in some embodiments, the RF waveguide 116 may include a coplanar waveguide (CPW) that includes additional conductive elements (e.g., a ground conductor). As another example, the track 118 and / or the RF electrode segment group 120 of the RF waveguide 116 may be connected to a plurality of RF electrodes. Figure 1A and Figure 1B For example, the RF electrode segment set 120 may be arranged on the substrate 102 or on the dielectric layer 110 on the substrate 102 (eg, instead of above the rib-like structure 112).

[0036] As also shown, the electro-optic modulator 100 includes a conductive strip 122 between the first rib-like structure 112a and the second rib-like structure 112b. In some embodiments, the conductive strip 122 is in ohmic contact with a region of the first doped layer 104 (e.g., a region of the first doped layer 104 between the first rib-like structure 112a and the second rib-like structure 112b). An ohmic contact is a metal-semiconductor contact in which the current is proportional to the voltage defined by a fixed impedance. It is worth noting that although the conductive strip 122 described herein can in practice be in ohmic contact with a region of the first doped layer 104, as described herein, another type of contact can be used. For example, the contact between the conductive strip 122 and the region of the first doped layer 104 can be a "drain" Schottky diode contact, which will still enable photocurrent to be extracted from the modulator 100. As Figure 1AAs shown, the conductive tape 122 contacts the first doped layer 104 through the opening 110o in the dielectric layer 110. In some embodiments, the conductive tape 122 includes an ohmic contact layer 122oh and a capping layer 122c that form an ohmic interface. In some embodiments, the ohmic contact layer 122oh of the conductive tape 122 may include, for example, nickel germanium gold (NiGeAu), palladium germanium gold (PdGeAu), or another type of ohmic contact material. In some embodiments, the capping layer 122c of the conductive tape 122 may include, for example, a titanium / platinum / gold (Ti / Pt / Au) layer or another type of conductive material. It is worth noting that in the modulator 100, the conductive tape 122 is not directly connected to the bias electrode set 124 (see Figure 1B ).

[0037] In some embodiments, Figure 1B As shown, the length of the conductive tape 122 is greater than the total length of the first group of RF electrode segments 120a and the second group of RF electrode segments 120b. Therefore, in some embodiments, a given end of the conductive tape 122 extends beyond the end of the total length of the first and second groups of RF electrode segments 120. Alternatively, in some embodiments, the length of the conductive tape 122 can match (e.g., be equal to within a tolerance) the total length of the first group of RF electrode segments 120a and the second group of RF electrode segments 120b. Therefore, in some embodiments, a given end of the conductive tape 122 extends to the end of the total length of the first and second groups of RF electrode segments 120. Alternatively, in some embodiments, the length of the conductive tape 122 can be less than the total length of the first group of RF electrode segments 120a and the second group of RF electrode segments 120b. Therefore, in some embodiments, a given end of the conductive tape 122 does not extend beyond the end of the total length of the first and second groups of RF electrode segments 120. In some embodiments, as Figure 1B As shown, the conductive ribbon 122 includes a single conductive segment. Alternatively, in some embodiments, the conductive ribbon 122 can include at least two conductive segments (e.g., such that the conductive ribbon 122 includes at least two separate segments). In some embodiments, the region of the first doped layer 104 that is in ohmic contact with the conductive ribbon 122 is below the first region and the second region of the first doped layer 104 that are included in the first and second rib-like structures 112. Additionally, in some embodiments, the conductive ribbon is below the first region and the second region of the undoped layer 106 that are included in the first and second rib-like structures. In some embodiments, the conductive ribbon 122 can be in another position relative to the region of the rib-like structure 112 (e.g., as long as the conductive ribbon 122 is in direct contact with the first doped layer 104).

[0038] As also shown, the modulator 100 includes a bias electrode set 124. The bias electrode set 124 includes an electrode set associated with applying a bias voltage that enables operation of the modulator 100. In operation, the diode formed by the optical waveguide should be reverse biased, meaning that the bias electrode set 124 should have a positive voltage applied relative to the voltage applied to the contacts of the electrode segment set 120. Photocurrent is generated by light traveling through the region of the undoped layer 106 of the rib structure 112 that defines the optical waveguide (i.e., the "i" region). This photocurrent needs to be extracted by an external circuit connecting the bias electrode set 124 and the track 118 of the RF waveguide 116. In some embodiments, the bias electrode set 124 can be positive relative to the track 118 of the RF waveguide 116 (e.g., for a modulator 100 in which the first doped layer 104 is an n-type layer and the second doped layer 108 is a p-type layer). In some embodiments, the bias electrode set 124 provides an external bias connection for the modulator 100. In some embodiments, the conductive strip 122 is used to reduce the impedance between the bias electrode group 124 and the third region of the first doped layer 104 between the first rib structure 112a and the second rib structure 112b (i.e., the region of the first doped layer 104 that is in ohmic contact with the conductive strip), as described below.

[0039] As also shown, the modulator 100 includes an optical splitter 126 to split an input optical signal (e.g., a continuous wave light to be modulated when the continuous wave light passes through the modulator 100) to form a first optical signal to be propagated in a first optical waveguide defined by the first rib-like structure 112a and a second optical signal to be propagated in a second optical waveguide defined by the second rib-like structure 112b. Here, the first optical signal is a first portion of the continuous wave light that will be modulated when the first portion of the continuous wave light passes through the first optical waveguide of the modulator 100, and the second optical signal is a second portion of the continuous wave light that will be modulated when the second portion of the continuous wave light passes through the second optical waveguide of the modulator 100. As also shown, the modulator 100 may include an optical combiner 128 to combine the output of the first rib-like structure 112a (e.g., after applying a first RF signal during the propagation of the first optical signal through the modulation region 114) and the output of the second rib-like structure 112b (e.g., after applying a second RF signal during the propagation of the second optical signal through the modulation region 114) to form one or more output optical signals. In practice, the first RF signal and the second RF signal may actually be "two halves of the same RF signal". Tracks 118a and 118b are defined as a (single) RF waveguide 116 because an RF waveguide requires two tracks - a positive track and a negative track (as shown in modulator 100), or alternatively, a signal line and a ground line. Thus, in some embodiments, the first RF signal and the second RF signal may be positive and negative versions of each other.

[0040] In operation of the modulator 100, an input optical signal is split by the optical splitter 126 so that a first optical signal is transmitted in a propagation direction (eg, in a direction) in a first optical waveguide defined by the first rib-shaped structure 112a. Figure 1B 106) and causes the second optical signal to propagate in the propagation direction in the second optical waveguide defined by the second rib-like structure 112b. Here, the given optical signal travels along the rib-like structure 112 in the region of the undoped layer 106 of the rib-like structure 112 (e.g., in the "i" region). The junction formed by the given rib-like structure 112 is reverse biased, and therefore, the doping of the first doped layer 104 and the doping of the second layer 108 enable an electric field to be applied to the region of the undoped layer 106 in which the given optical signal travels. The refractive index of the region of the undoped layer 106 in the rib-like structure 112 depends on the electric field, meaning that the phase of the optical signal propagating in the region of the undoped layer 106 depends on the electric field. Therefore, the RF waveguide 116 (e.g., through the track 118 and the electrode segment group 120) can be used to apply an RF signal to the optical waveguide defined by the rib-like structure 112 so as to modulate the phase of the optical signal propagating therein. Here, the RF signal is applied in the same direction as the direction of propagation of the optical signal (e.g., in the propagation direction) and has a speed that matches the speed of the optical signal (e.g., such that the modulator 100 is a speed-matched traveling wave MZ modulator). The RF signal can be applied so that the phase shift in one optical waveguide (e.g., the first optical waveguide defined by the first rib-like structure 112a) is positive, while the phase shift in the other optical waveguide (e.g., the second optical waveguide defined by the second rib-like structure 112b) is negative (e.g., zero relative to the applied RF signal). This results in constructive and destructive interference of the optical signal in the optical combiner 128, which modulates the intensity of the output optical signal of the modulator 100.

[0041] As described above, due to the absorption of light in the first and second optical waveguides, a photocurrent is generated in the modulation region 114. In the modulator 100, the conductive strip 122 is in ohmic contact with the third region of the first doped layer 104 (e.g., the region between the first rib-like structure 112a and the second rib-like structure 112b), as described above. The ohmic contact of the conductive strip 122 with the third region of the first doped layer 104 enables the generated photocurrent flowing through the first doped layer 104 to be extracted from the modulator 100. For example, the conductive strip 122 has a lower impedance than the first doped layer 104, and thus provides a relatively lower impedance conductive path for the photocurrent (e.g., compared to the conductive path provided by the first doped layer 104). Therefore, the longitudinal sheet impedance of the conductive path to the bias electrode group 124 is reduced. As a result, the de-biasing effect is reduced or eliminated, meaning that all portions of the modulation region 114 are subject to substantially the same bias conditions regardless of the photocurrent level. This results in a lower switching voltage for the modulator 100 (e.g., at a given pre-modulator SOA current level), and further, reduces or eliminates the dependence of the switching voltage on optical power. In this way, electro-optical efficiency is improved while reducing setup complexity (e.g., because changing the pre-modulator SOA current level does not affect the bias conditions of the modulator 100).

[0042] As mentioned above, Figure 1A-1B are provided as examples. Other examples can be found in the Figure 1A-1B The examples described are different. Figure 1A-1B The number and arrangement of layers and elements shown in the figure are provided as examples. In practice, there may be additional layers or elements, fewer layers or elements, different layers or elements, or different Figure 1A-1B In addition, the layers or elements shown in FIG. Figure 1A-1B Two or more layers or elements shown in the figure may be implemented in a single layer or element, or Figure 1A-1B A single layer or element shown in FIG. 4 may be implemented as multiple distributed layers or elements.

[0043] Figure 2A-2B is a schematic diagram illustrating the difference between an equivalent circuit of a conventional semiconductor-based modulator and an equivalent circuit of the modulator 100 described herein including the conductive strip 122 .

[0044] As described above, when a semiconductor-based electro-optic modulator is DC biased during operation, some light is absorbed in the optical waveguide, which generates a photocurrent. Figure 2A is an example equivalent circuit of a conventional semiconductor-based electro-optic modulator that does not include the conductive strip 122. As shown in the figure, in the absence of the conductive strip 122, each modulation segment R n_sThe longitudinal sheet resistance of the region between the doped layers is significant, and therefore the photocurrent I induced in each segment ph A voltage drop V is induced across this impedance. n_s , thereby reducing the bias applied to the portion of the modulation region of a conventional semiconductor-based electro-optic modulator. The magnitude of the bias reduction increases with the distance from V sub As described herein, the bias reduction results in a decrease in electro-optical efficiency in the affected portion of a conventional semiconductor-based electro-optic modulator, which increases the switching voltage V pi In particular, due to I ph is related to the optical power, so V pi The increase will depend on the optical input power and the pre-modulator SOA current.

[0045] Figure 2B is an example equivalent circuit of the modulator 100 including the conductive strip 122. Figure 2B As shown, the longitudinal impedance becomes relatively negligible due to the ohmic contact of the conductive strip 122 to the first doped layer 104. Therefore, the entire modulation region 114 is subject to substantially the same bias conditions regardless of the photocurrent generated in the modulator 100. It is worth noting that the conductive strip 122 is not directly connected to the bias electrode in order to provide a reduction or elimination of the longitudinal sheet impedance.

[0046] As mentioned above, Figure 2A-2B are provided as examples. Other examples can be found in the Figure 2A-2B The examples described are different.

[0047] Figure 3A-3B is a schematic diagram illustrating example measurement results showing the improved performance of the modulator 100 described herein including the conductive strip 122 as compared to a conventional semiconductor-based electro-optic modulator. Figure 3A and Figure 3B The plot of the current versus bias voltage (V) for various pre-semiconductor SOA current levels (30 milliamperes (mA), 60 mA, 100 mA, and 150 mA) is shown. cm ) draws the switch voltage (V pi ). Figure 3A exemplifies the performance of a conventional semiconductor-based electro-optic modulator (which does not include the conductive strip 122), while Figure 3B The performance of the modulator 100 including the conductive strip 122 is illustrated.

[0048] By comparison Figure 3A and Figure 3B It can be seen that the switching voltage V piThe optical power dependence of is reduced in the modulator 100 including the conductive strip 122, or at the bias voltage V cm For example, in a conventional semiconductor-based electro-optic modulator, at a bias voltage V of 5.5 volts (V), cm Under, the switch voltage V pi As the pre-modulator SOA current increases (ie, as the input optical power increases). However, in the modulator 100 including the conductive strip 122, at a bias voltage V cm For a given pre-modulator SOA current level, the switch voltage V pi is reduced, and in addition, as the pre-modulator SOA current increases, the switch voltage V pi By reducing or eliminating the debiasing effect, the switching voltage V pi This reduction and switching voltage V pi The reduced dependence on optical input power allows the bias conditions to be substantially the same across the modulation region 114 regardless of the photocurrent level.

[0049] As mentioned above, Figure 3A-3B are provided as examples. Other examples can be found in the Figure 3A-3B The examples described are different.

[0050] The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Modifications and variations may be made based on the foregoing disclosure, or modifications and variations may be obtained from the practice of the embodiments. In addition, unless the foregoing disclosure explicitly provides a reason why one or more embodiments are not combined, any embodiments described herein may be combined.

[0051] Even though specific combinations of features are described in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of the various embodiments. In fact, many of these features can be combined in ways that are not specifically described in the claims and / or disclosed in the specification. Although each dependent claim listed below may be directly subordinate to only one claim, the disclosure of the various embodiments includes the combination of each dependent claim with each other claim in the claim set. As used herein, a phrase referring to "at least one" in a list of items refers to any combination of those items, including single members. As an example, "at least one of a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination with multiple identical items.

[0052] When a component or one or more components (e.g., a laser emitter or one or more laser emitters) is described or claimed (within a single claim or across multiple claims) as performing multiple operations or being configured to perform multiple operations, the language is intended to broadly cover a variety of architectures and environments. For example, unless otherwise expressly stated (e.g., via the use of "first component" and "second component" or other language that distinguishes components in the claims), the language is intended to cover a single component that performs or is configured to perform all operations, a group of components that collectively perform or are configured to perform all operations, a first component that performs or is configured to perform a first operation and a second component that performs or is configured to perform a second operation, or any combination of components that perform or are configured to perform operations. For example, when a claim has the form "one or more components that are configured to: perform X; perform Y; and perform Z", the claim should be interpreted to mean "one or more components configured to perform X; one or more (possibly different) components configured to perform Y; and one or more (possibly different) components configured to perform Z".

[0053] Unless clearly described as such, the elements, actions or instructions used herein should not be interpreted as key or necessary. In addition, as used herein, the articles "one" and "an" are intended to include one or more projects, and can be used interchangeably with "one or more". In addition, as used herein, the article "said" is intended to include one or more projects quoted in conjunction with the article "said", and can be used interchangeably with "one or more". In addition, as used herein, the term "group" is intended to include one or more projects (for example, a combination of related projects, unrelated projects, or related and unrelated projects), and can be used interchangeably with "one or more". In the case of only intending a project, the phrase "only one" or similar language is used. In addition, as used herein, the term "has", "have", "having" etc. are intended to be open terms. In addition, unless otherwise clearly stated, the phrase "based on" is intended to represent "at least partially based on". In addition, as used herein, the term "or" is intended to be inclusive when used in series, and can be used interchangeably with "and / or", unless otherwise clearly stated (for example, if used in combination with "either" or "only one in". In addition, for ease of description, spatially relative terms such as "below," "lower," "above," "upper," etc. may be used herein to describe the relationship of one element or feature to another (one or more) element or (one or more) feature as shown in the figures. Spatially relative terms are intended to cover different orientations of devices, equipment, and / or elements in use or operation in addition to the orientations depicted in the figures. Devices may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein may likewise be interpreted accordingly.

Claims

1. An electro-optic modulator, comprising: A radio frequency (RF) modulation area, the RF modulation area comprising: a first optical waveguide for propagating a first optical signal traveling in a propagation direction; a second optical waveguide for propagating a second optical signal traveling in the propagation direction; a first set of electrode segments for applying a first RF signal to the first optical waveguide in association with modulating the first optical signal, the first RF signal being provided by a first track of the RF waveguide and travelling in the propagation direction; a second set of electrode segments for applying a second RF signal to the second optical waveguide in association with modulating the second optical signal, the second RF signal being provided by a second track of the RF waveguide and travelling in the propagation direction; and a conductive strip for enabling extraction from the electro-optic modulator of a photocurrent generated in the first and second optical waveguides and flowing through a doped layer below the first and second optical waveguides, the conductive strip being between the first and second optical waveguides and in ohmic contact with the doped layer.

2. An electro-optic modulator according to claim 1, wherein the conductive strip provides a lower impedance conduction path for the photocurrent than a conduction path provided by the doped layer.

3. An electro-optic modulator according to claim 1, wherein the conductive strip is not directly connected to an external bias connection of the electro-optic modulator.

4. The electro-optic modulator of claim 1, wherein the conductive strip comprises an ohmic contact layer and a capping layer.

5. The electro-optic modulator of claim 1, wherein the length of the conductive strip is greater than or equal to the total length of the first set of electrode segments and the total length of the second set of electrode segments.

6. The electro-optic modulator of claim 1, wherein ends of the conductive strip extend beyond ends of the first set of electrode segments and ends of the second set of electrode segments.

7. An electro-optic modulator as claimed in claim 1, wherein the conductive strip comprises a single conductive segment.

8. The electro-optic modulator of claim 1, wherein the conductive strip comprises at least two conductive segments.

9. The electro-optic modulator of claim 1, wherein the conductive strip contacts the doped layer through an opening in a dielectric layer above the doped layer.

10. The electro-optic modulator of claim 1, wherein the electro-optic modulator is a III-V semiconductor modulator.

11. An electro-optic modulator, comprising: substrate; a first doped layer above the substrate; an undoped layer above the first doped layer; a second layer above the undoped layer, wherein the first region of the first doped layer, the first region of the undoped layer, the first region of the second layer and the first portion of the dielectric layer form a first rib-shaped structure, and wherein the second region of the first doped layer, the second region of the undoped layer, the second region of the second layer and the second portion of the dielectric layer form a second rib structure; a first group of electrode segments, the first group of electrode segments being above the first rib-like structure; a second group of electrode segments, the second group of electrode segments being above the second rib-like structure; a first track of a radio frequency (RF) waveguide, the first track being electrically connected to the first set of electrode segments; a second track of the RF waveguide, the second track being electrically connected to the second set of electrode segments; as well as A conductive strip is in ohmic contact with a third region of the first doped layer, wherein the third region of the first doped layer is between the first region of the first doped layer and the second region of the first doped layer.

12. The electro-optic modulator of claim 11, wherein the conductive strip is used to enable extraction from the electro-optic modulator of a photocurrent generated in the rib-like structure and the second rib-like structure and flowing through the first doped layer.

13. The electro-optic modulator of claim 11, wherein the conductive strip is not directly connected to an external bias connection of the electro-optic modulator.

14. The electro-optic modulator of claim 11, wherein the conductive strip comprises an ohmic contact layer and a capping layer over the ohmic contact layer.

15. The electro-optic modulator of claim 11, wherein the conductive strip comprises a single conductive segment.

16. The electro-optic modulator of claim 11, wherein the conductive strip contacts the doped layer through an opening in a dielectric layer above the doped layer.

17. The electro-optic modulator of claim 11, wherein the electro-optic modulator is a III-V semiconductor modulator.

18. A semiconductor-based modulator comprising: A radio frequency (RF) modulation area, the RF modulation area comprising: a first optical waveguide for propagating a first optical signal traveling in a propagation direction; a second optical waveguide for propagating a second optical signal traveling in the propagation direction; an RF waveguide for applying a first RF signal to the first optical waveguide and a second RF signal to the second optical waveguide, the first RF signal and the second RF signal traveling in the propagation direction; and A conductive strap for reducing impedance on a conductive path between an external bias connection of the semiconductor-based modulator and doped regions beneath the first and second optical waveguides to enable extraction of photocurrent flowing through the doped regions from the semiconductor-based modulator.

19. The semiconductor-based modulator of claim 18, wherein: The conductive strip is in ohmic contact with the doped region.

20. The semiconductor based modulator of claim 18, wherein the conductive strip is not directly connected to the external bias connection.

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