Phase-tuned parity-time symmetric directional coupler

Abstract

The present disclosure relates to phase-tuned parity-time symmetric directional couplers. Embodiments disclosed herein provide devices and methods for obtaining parity-time (PT) symmetric directional couplers by improved phase tuning and separate optical gain and optical loss tuning. The present disclosure integrates phase tuning and optical gain / loss tuning structures into the waveguide of the directional coupler disclosed herein. In some examples, the directional coupler disclosed herein integrates one or more hybrid metal oxide semiconductor capacitors (MOSCAPs) formed by a dielectric layer between two semiconductor layers and providing phase tuning by plasma dispersion and / or carrier accumulation according to voltage bias polarity, and one or more optically active media that provide optical gain or loss tuning according to voltage bias polarity.

Description

Technical Field

[0001] The present disclosure relates to phase-tuned parity-time symmetric directional couplers. Background Art

[0002] Parity time (PT) symmetric directional couplers require a balance between gain and loss in the upper and lower waveguides to achieve efficient optical switching. Tuning both the gain element and the loss element introduces a refractive index difference that can reduce the power extinction of the optical switch. By adding a separate hybrid semiconductor metal-on-semiconductor capacitor (MOSCAP), there is an additional knob to tune the refractive index (optical phase) and achieve improved power extinction.

[0003] The current configuration does not provide a way to independently control the gain / loss and phase difference between the two legs. Summary of the invention

[0004] According to a first aspect of the present disclosure, a hybrid III-V / silicon device is provided, comprising: a first silicon layer, the first silicon layer being arranged above a buried oxide BOX layer, wherein the first silicon layer comprises: a first doped region, the first doped region having a first groove, a second doped region, the second doped region having a second groove, a first gap region, the first gap region being arranged between the first doped region and the second doped region; a first oxide layer, the first oxide layer being arranged above the first doped region and the second doped region; a first mesa, the first mesa being arranged on the first doped region of the first silicon layer, wherein the first mesa comprises: a first III-V family layer, the first III -V family layer is arranged above the first oxide layer; a first optically active region, the first optically active region is arranged above the first III-V family layer; and a second III-V family layer, the second III-V family layer is arranged above the optically active region; and a second table, the second table is arranged on the second doped region of the first silicon layer, wherein the second table includes: a third III-V family layer, the third III-V family layer is arranged above the first oxide layer; a second optically active region, the second optically active region is arranged above the third III-V family layer; and a fourth III-V family layer, the fourth III-V family layer is arranged above the second optically active region.

[0005] According to a second aspect of the present disclosure, a directional coupler is provided, comprising: a buried oxide BOX layer; a first metal oxide semiconductor (MOS) capacitor, the first MOS capacitor being formed on the BOX layer, the first MOS capacitor comprising: a first optical waveguide; a first cathode, the first cathode comprising a first material and being formed in the first optical waveguide; a first anode, the first anode being formed in the first optical waveguide, the first anode comprising a second material different from the first material; and a first dielectric, the first dielectric being arranged between the first cathode and the first anode, the first dielectric comprising an oxide of the first material and an oxide of the second material, wherein the first MOS capacitor is defined between the first anode and the first cathode; and a first mesa, the first mesa being arranged on the first MOS capacitor, the first mesa comprising: a first anode; a first optically active region, the first optically active region being arranged on the first anode; and a first semiconductor layer, the first semiconductor layer comprising the second material and being arranged on the optically active region; and a second optical waveguide, the second optical waveguide being arranged on the BOX layer, adjacent to the first optical waveguide, and having a first gap between the first optical waveguide and the second optical waveguide.

[0006] According to a third aspect of the present disclosure, a method for tuning a directional coupler is provided, the method comprising: applying a first voltage bias to a first metal oxide semiconductor (MOS) capacitor, the first MOS capacitor being formed in a first optical waveguide; modulating a first refractive index of the first optical waveguide by adjusting the first voltage bias, wherein, in response to the first voltage bias, the first refractive index changes based on a carrier concentration in the first MOS capacitor; applying a second voltage bias to a first table disposed on the first MOS capacitor, the first table comprising a first optically active region; modulating an optical gain or optical loss introduced into the first optical waveguide by the first table by adjusting the second voltage bias, wherein, in response to the second voltage bias, the optical gain or the optical loss changes based on a carrier concentration in the first optically active region; and tuning a gain-loss ratio and a refractive index difference between the first optical waveguide and a second optical waveguide based on modulating the first refractive index and the optical gain or the optical loss. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The present disclosure is described in detail according to one or more different embodiments with reference to the following drawings. The drawings are provided for illustrative purposes only and depict only typical or example embodiments.

[0008] Figure 1 An example directional coupler is illustrated.

[0009] FIG. 2A to FIG. 2CIllustration of light wave propagation in an example directional coupler.

[0010] FIG. 3A to FIG. 3C The transmission of an example parity-time (PT) symmetric directional coupler is illustrated for varying refractive index differences between the gain and loss waveguides.

[0011] FIG. 4A to FIG. 4D An example heat map depicting the transmission intensity matrix of an example PT-symmetric directional coupler having a refractive index difference between the gain waveguide and the loss waveguide is illustrated.

[0012] FIG. 5A to FIG. 5D An example heat map depicting a transmission intensity matrix for another example PT-symmetric directional coupler having another refractive index difference between the gain waveguide and the loss waveguide is illustrated.

[0013] Fig. 6A and Figure 6B An example metal oxide semiconductor (MOS) optical modulator that may be implemented in the techniques disclosed herein is illustrated.

[0014] Fig. 7A and Figure 7B shows that at various dielectric thicknesses, applied to Fig. 6A and Figure 6B Simulated relationship between voltage and mode refractive index change and FCA change of an optical modulator.

[0015] Fig. 8A Illustrated is a top view of an example directional coupler according to implementations disclosed herein.

[0016] Figure 8B An example directional coupler is shown along Fig. 8A A cross-sectional view taken along line BB'.

[0017] Figure 8C Another example directional coupler is shown. Fig. 8A A cross-sectional view taken along line BB'.

[0018] Fig. 9 The present invention illustrates an embodiment according to the present invention. FIG. 8A to FIG. 8C Example of carrier concentration migration within a directional coupler.

[0019] Fig.10 is an example flow chart illustrating an example process for tuning a directional coupler according to implementations disclosed herein.

[0020] Fig.11 is an example computer system that can be used to implement various features of the various optical devices disclosed herein.

[0021] The drawings are not exhaustive and do not limit the disclosure to the precise forms disclosed. DETAILED DESCRIPTION

[0022] Examples provided herein are apparatus and methods for obtaining a parity time (PT) symmetric directional coupler. A PT symmetric directional coupler requires a well-balanced gain-loss ratio between the waveguides of the directional coupler to achieve efficient optical switching. Therefore, embodiments disclosed herein provide for modulating the optical loss of a first waveguide separately from the optical gain of a second waveguide to achieve tuning of the gain-loss ratio. Embodiments herein also provide for modulation of the optical gain of a second waveguide.

[0023] However, tuning optical gain and / or optical loss may cause fluctuations in the refractive index of the waveguide, which can degrade the performance of the directional coupler. Therefore, embodiments of the present invention integrate hybrid metal oxide semiconductor capacitors (MOSCAPs) into one or both waveguides, thereby enabling the refractive index to be tuned individually and simultaneously. Through the gain-loss ratio and the refractive index, embodiments disclosed herein provide a PT-symmetric directional coupler that can be used for efficient optical switching.

[0024] An example of a hybrid MOSCAP utilized by the embodiments disclosed herein can be formed by a thin dielectric layer between two semiconductor layers having different materials, each semiconductor layer being formed in a waveguide of the embodiments disclosed herein. In one example, the dielectric layer is an interface oxide layer between a bandgap III-V compound semiconductor material layer (referred to herein as a III-V material) and a silicon (Si) layer or other bandgap IV compound semiconductor layers (referred to herein as IV materials) such as germanium, silicon carbide, silicon germanium, etc. Depending on the bias polarity, the voltage bias applied to the MOSCAP provides phase tuning through a plasma dispersion effect or a carrier accumulation effect. For example, a carrier accumulation effect (with a positive voltage bias or a forward voltage bias) can change the phase and reduce the effective refractive index of the waveguide, while a plasma dispersion effect (with a negative voltage bias or a reverse voltage bias) can increase the effective refractive index. Therefore, controlling the voltage bias applied to the MOSCAP according to the embodiments disclosed herein enables the refractive index of the corresponding waveguide to be changed. The disclosed example hybrid MOSCAP uses standard III-V materials and can be manufactured together with components for modulating gain or loss.

[0025] Implementing a controllable and manufacturable PT-symmetric directional coupler with an integrated hybrid MOSCAP as described herein can significantly reduce the footprint of large optical neural networks, optical machine learning accelerators, programmable photonic networks, and RF photonic devices. For example, a directional coupler including the embodiments disclosed herein can be used in a dense wavelength division multiplexing (DWDM) photonic integrated circuit (PIC). DWDM is an optical multiplexing technology used to increase bandwidth on existing fiber optic networks. The DWDM PIC architecture includes photonic devices that are fully integrated on a single manufacturing platform. Many devices on the PIC can be implemented with higher performance and a smaller footprint by using the embodiments disclosed herein that provide improved optical switching and power distribution. For example, some traditional directional couplers that use thermal phase shifters to complete power transmission may have a length of more than 75um, while the length of directional couplers that do not use thermal-based phase shifters may be in the order of millimeters. Compared with traditional directional couplers, the devices and methods disclosed herein provide ultra-short optical power dividers and switches. For example, the embodiments disclosed herein provide a PT-symmetric directional coupler that is capable of optical manipulation at the nanoscale and includes sub-wavelength components. As an illustrative example, the embodiments disclosed herein can provide a directional coupler having a length of about 25 μm or less, depending on the gain-loss ratio achieved. Thus, the embodiments disclosed herein require a significantly reduced footprint compared to conventional directional couplers, while also providing the efficient switching and power distribution achieved by a PT-symmetric directional coupler.

[0026] Furthermore, the fabrication of the embodiments disclosed herein is fully compatible with existing and future PIC designs without the need for additional processes. For example, the MOSCAP utilized in the directional coupler disclosed herein can be formed using fabrication techniques and processes that are combined with fabrication processes of the various components that make up the PIC (e.g., lasers, modulators, detectors, etc.). Thus, the embodiments herein do not complicate the fabrication and / or assembly of the PIC and other systems utilizing the devices disclosed herein.

[0027] As mentioned above, the operation of a PT-symmetric directional coupler requires a well-balanced gain-loss ratio within the directional coupler. Current systems do not have a way to adjust the optical losses to tune the gain-loss ratio. For example, an exemplary current system introduces gain via a gallium arsenide (GaAs) or aluminum gallium arsenide (AlGaAs) material that provides a fixed loss through chromium (Cr) metal absorption. Another exemplary system uses a lithium niobate (LiNO3) platform and optical pumping via an amplitude mask. These existing systems can introduce gain, but have fixed losses, and these existing systems do not provide a means for modulating the optical losses. In addition, as described above, changes in the gain-loss ratio cause changes in the refractive index, which degrades the performance of the system, and existing directional couplers cannot provide a means for tuning the refractive index separately from the gain or loss. The embodiments disclosed herein utilize MOSCAP as a phase shifter, which provides a modulation efficiency V that is lower than the modulation efficiency provided by conventional phase shifters. π L, for example, V π L<0.3V / cm.

[0028] Thus, the embodiments disclosed herein provide individually adjustable gain and loss, while providing tuning of phase and refractive index. By utilizing the embodiments disclosed herein, high performance PT symmetric directional couplers that can provide ultra-short optical switches and optical power dividers can be obtained on a silicon photonics platform compared to conventional directional couplers. Thus, the footprint of large systems can be reduced. In addition, compared to other currently used phase shifters (such as micro heaters), the refractive index tuning provided by the hybrid MOSCAP disclosed herein provides ultra-low power operation, for example, V π L<0.3V / cm, while consuming nanowatts of power.

[0029] In addition, the embodiments of the present invention allow for unit matrix transformations, which is important for neural networks. Unitary matrix transformations require lossless components. The embodiments of the present invention can use optical gain to compensate for optical losses within the system to achieve the lossless components required to achieve unit matrix transformations. Therefore, the embodiments of the present invention are applicable and can be implemented as part of a neural network system.

[0030] It should be noted that the terms "optimize," "optimal," and the like as used herein may be used to mean to achieve or attain as efficient or perfect a performance as possible. However, one of ordinary skill in the art reading this document will recognize that perfection is not always achievable. Thus, these terms may also encompass achieving or attaining the best or efficient or practical performance possible under given circumstances, or achieving or attaining a better performance than would be achievable using other settings or parameters.

[0031] Figure 1An example directional coupler 100 is illustrated. The directional coupler 100 depicts an example 2×2 directional optical coupler including a first waveguide 110 and a second waveguide 120. The first waveguide 110 includes an input port 112 and an output port 114. The second waveguide 120 includes an input port 122 and an output port 124. The first waveguide 110 defines a first leg of the directional coupler 100, and the second waveguide 120 defines a second leg of the directional coupler 100. The directional coupler 100 may be used as an optical switch or other optical device.

[0032] The directional coupler 100 includes a coupling length L c of the coupling region 102. Within the coupling region, light propagating in one waveguide may be tapped into another waveguide (e.g., a portion of the light propagating in one waveguide is transmitted into another waveguide). The tapped portion of the light may then propagate in the other waveguide and be output via an output port of the other waveguide. Additionally, the portion of light remaining in the one waveguide may be output from the output port of the one waveguide. Furthermore, the light output from either output port may depend on propagation losses, such as, but not limited to: excess loss (e.g., the ratio of total input power to total output power); polarization-dependent loss (e.g., the ratio of maximum transmission to minimum transmission due to the polarization state in the coupler); optical return loss / directivity (e.g., the portion of input light that exits through an input port instead of the intended output port); insertion loss (e.g., the ratio of input power to output power at one output port of the coupler, and in the case of a 2×2 coupler, insertion loss may be determined for each output port).

[0033] The amount of light that is tapped into the other waveguide can depend on the coupling ratio between the two waveguides (e.g., 50:50, 90:10, or any coupling ratio desired for a given application). The coupling ratio is the ratio of the optical power at each output port to the sum of the total power at both output ports as a function of wavelength. The coupling ratio can be calculated based on the measured insertion loss (e.g., the loss of signal power expressed in decibels (dB) due to the insertion of a device in a transmission line or optical fiber).

[0034] As an example, the first light 116 is input to the input port 112 of the first waveguide 110 and propagates toward the coupling region 102. In the coupling region 102, at least a portion 118 of the first light 116 is transmitted to the second waveguide 120 based on the coupling ratio of the directional coupler 100. The transmitted portion 118 is then transmitted to the second waveguide 120 via a transmission light intensity matrix T 12 The remaining portion 119 of the first light 116 propagating in the first waveguide 110 is outputted through the output port 124 of the first waveguide 110 as described below. 11The output power at each output port 114 and 124 may be based on one or more losses as described above.

[0035] In another example, the second light 126 is input into the input port 122 of the second waveguide 120 and propagates toward the coupling region 102. In the coupling region 102, based on the coupling ratio of the directional coupler 100, at least a portion 128 of the second light 126 is transmitted into the first waveguide 110. The transmitted portion 128 is then transmitted to the first waveguide 110 via the transmission light intensity matrix T 21 The remaining portion 129 of the first light 116 propagating in the first waveguide 110 is outputted through the transmission light intensity matrix T 22 In one case, the second light 126 may be input into the directional coupler 100 in place of the first light 116. In another case, the second light 126 may be input into the directional coupler 100 simultaneously with the first light 116 or in alternating light pulses. In this case, the output port 114 may output the remaining portion 119 of the first light 116 and the transmitted portion 128 of the second light 126, while the output port 124 outputs the transmitted portion 118 of the first light 116 and the remaining portion of the second light 129.

[0036] For example, based on the gain-loss ratio between waveguides, the directional coupler can be implemented as a PT-symmetric directional coupler. Recent advances in nanofabrication technology have facilitated the emergence of artificial structures such as PT-symmetric devices that exploit PT symmetry. PT-symmetric devices enable light manipulation at the nanoscale and can include subwavelength components that narrow the miniaturization gap between photonics and electronics. Although propagation losses (such as those described above) are generally considered to be detrimental in optical systems, propagation losses can play a positive role in optical devices, for example, when providing a PT-symmetric directional coupler.

[0037] When a certain amount of loss is introduced into the system, the PT-symmetric directional coupler can work as an efficient directional coupler (e.g., optical switch). Figure 1 The directional coupler 100 may be implemented as a PT-symmetric directional coupler by introducing optical gain into the first waveguide 110 (referred to herein as a gain waveguide) and introducing optical loss (eg, propagation loss) into the second waveguide 120 (referred to herein as a loss waveguide). FIG. 6A to FIG. 10 Example directional couplers for introducing optical gain and optical loss into coupled waveguides are provided.

[0038] By changing the gain level and loss level in each waveguide relative to each other (e.g., changing the gain-loss ratio within the coupling region 102), a PT-symmetric directional coupler can be obtained, whereby the output signal from the directional coupler can be suddenly modulated based on a small change in the gain-loss ratio. This property stems from the eigenvalues ​​of the two waveguides, which merge when the gain-loss ratio reaches a critical threshold (referred to herein as an exception point). The exception point has a singularity that provides an abrupt change in the eigenvalue from the real axis to the imaginary axis in response to a small change in the gain-loss ratio. Therefore, a large differential gain can be achieved by a moderate change in gain and / or loss (which changes the gain-loss ratio near the exception point). For example, a PT-symmetric directional coupler can dynamically switch the light output at the output port 114 from the first light 116 input into the first waveguide 110 to the second light 126 input into the second waveguide 122 by slightly modulating the gain and / or loss to tune the gain-loss ratio between the waveguides in the coupling region 102. The intensity of light output from such a PT-symmetric directional coupler can be the same or approximately the same as the intensity at the input, regardless of which light is output from the system.

[0039] For example, FIG. 2A to FIG. 2C An example conventional directional coupler is shown ( Figure 2A ) and PT symmetrical directional couplers, where the gain-loss ratio is lower than the exceptional point ( Figure 2B ), and equal to or above the exception point ( Figure 2C ). FIG. 2A to FIG. 2C The figure shows how light input into a directional coupler is transmitted under different operating conditions. FIG. 2A to FIG. 2C Directional couplers 200a-200c are shown in the figure. Each directional coupler 200a-200c (collectively referred to as directional coupler 200 herein) is substantially the same, having a first waveguide 201 and a second waveguide 203, except that FIG. 2A to FIG. 2C The gain-loss ratio decays near the exceptional point.

[0040] exist Figure 2A In the conventional directional coupler 200a, propagation loss is minimized and no gain is added to the system. In this case, light input into the first waveguide 201 (as shown by arrow 202) is transmitted to the second waveguide 203, for example, as described above. The light transmitted from the first waveguide 201 to the second waveguide 203 is essentially reciprocal (for example, there is path dependence), so that the input light is output from both waveguides. Similarly, light input into the second waveguide (as shown by arrow 204) is transmitted to the first waveguide 201 having a reciprocal property.

[0041] exist Figure 2BIn the PT-symmetric directional coupler 200b, loss and gain are added to the system so that the gain-loss ratio is lower than the exceptional point. In the directional coupler 200b, the first waveguide 201 adds gain to the light propagating therein, while the second waveguide 203 introduces loss. In this case, the light input into the first waveguide 201 (as shown by arrow 202) is transmitted to the second waveguide 203, for example, as described above. In this case, the output power depends on the path previously taken. Therefore, the power at the output of each waveguide depends on which waveguide the light is input into.

[0042] exist Figure 2C In the PT symmetrical directional coupler 200c, loss and gain are added to the system so that the gain-loss ratio is at or above the exceptional point. Figure 2B As shown, the first waveguide 201 of the directional coupler 200b introduces gain, while the second waveguide 203 introduces loss. In this case, the reciprocal property no longer occurs and the output power can be fully switched, regardless of the coupling length and independently of the path previously taken (e.g., in these examples, regardless of which waveguide the light is input into, the output power will always come out of waveguide 201). For example, light input into the first waveguide 201, represented by arrow 202, is not transmitted to the second waveguide 203, while light input into the second waveguide 203, represented by arrow 204, is fully transmitted (e.g., switched) to the first waveguide 201. Therefore, the output power can be substantially fully switched between the light input into each respective waveguide (e.g., approximately 100% of the input light will be output from the gain waveguide). For example, as combined with Figure 3A Described in more detail, under certain conditions, the output on the lossy waveguide can be as low as -50 dB, which may be substantially close to zero, meaning that substantially all of the power is output from the gain waveguide.

[0043] The PT-symmetric directional coupler can dynamically switch light from one waveguide to another, thereby delivering an output intensity that is substantially the same as that injected into the input waveguide. c , the light output from this PT-symmetric directional coupler can be modeled by the transmission matrix, and the coupling length is given by Definition. This directional coupler has a coefficient m ij The transmission matrix M(z) is provided as:

[0044]

[0045] where z is the propagation distance, κ is the coupling coefficient, and g 1 is the gain introduced by the first waveguide (e.g., waveguide 110), and 2 (Also known as -g 2) is the propagation loss introduced by the second waveguide (e.g., waveguide 120), and a variable Ω representing the coupling coefficient detuning is provided as:

[0046]

[0047] δ is the waveguide propagation constant in the presence of combined gain / loss (β j ) is detuned, which is given by:

[0048]

[0049] where β 1 is the propagation constant of the first waveguide, β 2 is the propagation constant of the second waveguide, and Δ im is the combined virtual detuning (e.g., |gain| + |loss|). im Provided as:

[0050]

[0051] According to Equations 1-4, in response to a complete crossing from one waveguide to another when δ=0 (Ω=κ), for light injected through the i-th waveguide, the transmitted light intensity matrix T at the output of the j-th waveguide is ij It can be given by the following formula, where z is the coupling length L c :

[0052] T ij =|M ij | 2 Equation 5

[0053] Therefore, reference Figure 1 , using the above equation, the transmitted light intensity matrix of the output light portion 118 (e.g., the first light 116 input into the first waveguide 110 and transmitted into the second waveguide 120 and output from the second waveguide 120) can be calculated as T 12 Similarly, the transmitted light intensity matrix of the output light portion 119 (eg, the first light 116 input into and output from the first waveguide 110) can be calculated as T 11 The transmitted light intensity matrix of the output light portion 128 (eg, the second light 126 input into the second waveguide 120 and transmitted into the first waveguide 110 and output from the first waveguide 110) can be calculated as T 21 ; and the transmitted light intensity matrix of the output light portion 129 (eg, the second light 126 input into and output from the second waveguide 120) can be calculated as T 22 .

[0054] As mentioned above, the operation of the PT-symmetric directional coupler requires balancing the gain and loss of each waveguide to achieve a gain-loss ratio at or above the exceptional point. When such conditions are met, the PT-symmetric directional coupler can achieve efficient optical switching (e.g., optical switching using a shorter device length than a conventional directional coupler). However, tuning the gain and loss of each waveguide simultaneously can cause a refractive index difference. For example, tuning the gain and / or loss is related to the Kramer-Kronig relation and the linewidth enhancement factor, as known in the art. In addition, tuning the gain can also cause heat, which will change the refractive index within the waveguide.

[0055] FIG. 3A to FIG. 3C The transmission of an example PT-symmetric directional coupler is illustrated for varying refractive index differences between the gain and loss waveguides. FIG. 3A to FIG. 3C is the simulation of light input into the gain waveguide, and the transmitted light power output from the gain waveguide (e.g., the matrix T calculated according to the above equations 1-5) 11 ) and the transmitted optical power output from the lossy waveguide (e.g., matrix T 12 ) is plotted as a function of the gain added by the gain waveguide, where the loss added by the loss waveguide remains constant. FIG. 3A to FIG. 3C In each of these, certain parameters remain constant, for example, the coupling length (L c ) is 25 μm, the optical wavelength (λ) is 1.31 μm, and the actual length L of the gain loss part is L c 2.1 times (note that Figure 1 L and L c The markings are not drawn to scale and are provided for illustration purposes only), and the loss introduced is -10cm -1 .for Figure 3A , 3B and 3C, the refractive index difference (Δn) between the gain waveguide and the loss waveguide is 10e -6 , 10e -4 and 10e -3 .

[0056] FIG. 3A to FIG. 3C The power extinction and outliers are plotted as a function of the gain-loss ratio for each refractive index difference (Δn). Figure 3A The transmitted light intensity matrix T is shown 11 At about 870cm -1 Power extinction 302 under the gain of transmitted light intensity matrix T 12 At about 399cm -1 The power extinction at the gain of 304 and at about 1125cm -1An exceptional point 310 at a gain of , where light is input into a gain waveguide (eg, waveguide 110) of the directional coupler. Figure 3B The transmitted light intensity matrix T is shown 11 At about 870cm -1 The power extinction under the gain of 312, the transmitted light intensity matrix T 12 At about 399cm -1 The power extinction at a gain of 314 and at about 1125 cm -1 Exception point 320 at a gain of , where light is input into the gain waveguide (e.g., waveguide 110) of the directional coupler. Figure 3A and Figure 3B It can be seen that 10e -6 The refractive index difference provides better power extinction than minus 40 dB (for example, for T 11 is almost negative 50dB, and for T 12 Almost -70 dB). However, as the refractive index difference increases, the power extinction decreases, e.g. Figure 3B As shown, the power extinctions 312 and 314 are slightly higher than -10 dB and about -25 dB, respectively. Figure 3C 10e -3 ), power extinction and exception points no longer exist.

[0057] FIG. 4A to FIG. 4D An example heat map is shown, which depicts the transmission intensity matrix (T ij ), where the refractive index difference between the gain waveguide and the loss waveguide is 10e -6 . Figure 3A The curve T 11 and T 12 Can correspond to Figure 4A T11 and Figure 4B Horizontal slices of T12 taken along a single length. FIG. 5A to FIG. 5D An example heat map is shown, which depicts the transmission intensity matrix (T ij ), where the refractive index difference between the gain waveguide and the loss waveguide is 10e -3 . Transmitted intensity matrix (T ij ) are depicted as heat maps, where the color in each heat map corresponds to the transmitted intensity value in dB, as indicated in the legend, plotted as a function of length L as a function of gain. The dashed line in each heat map corresponds to a transmitted intensity of 0 dB. Figure 4A and Figure 5A Corresponding to the transmission intensity matrix T 11 ; Figure 4B and Figure 5B Corresponding to the transmission intensity matrix T12 ; Figure 4C and Figure 5C Corresponding to the transmission intensity matrix T 21 ; Figure 4C and Figure 5C Corresponding to the transmission intensity matrix T 22 . Calculate the transmission intensity matrix for each heat map, where the coupling length (L c ) is 25 μm, the optical wavelength (λ) is 1.31 μm, and the introduced loss is -10 cm -1 .

[0058] FIG. 4A to FIG. 4D The diagram shows that optical switching can be achieved regardless of how the actual length of the gain-loss section is adjusted by adjusting the gain-loss ratio. FIG. 4A to FIG. 4D As shown, when the gain increases, as the loss at -10cm -1 However, when the refractive index difference becomes too large (e.g., 10e -3 ), the power extinction is reduced, such as FIG. 5A to FIG. 5D Therefore, as mentioned above, as the refractive index difference between the first waveguide and the second waveguide becomes larger, the PT symmetry decreases, thereby hindering the performance of the directional coupler.

[0059] Thus, embodiments of the technology disclosed herein provide a directional coupler that can be tuned to obtain PT symmetry. For example, the gain and / or loss introduced into the waveguide can be modulated so as to tune the gain-loss ratio near the exception point of the PT symmetry. For example, a first table including a first optically active region can be provided relative to a first waveguide. A voltage bias can be applied to the first table to induce optical gain or optical loss in the first waveguide based on a change in carrier concentration within the first table. By controlling the bias applied to the first table, the gain or loss can be changed to optimize the gain-loss ratio relative to the exception point. Whether gain or loss is induced can be based on the polarity of the bias (e.g., forward bias or reverse bias). Additionally or alternatively, a second table including a second optically active region can be provided relative to a second waveguide. A separate voltage bias can be applied to the second table to induce optical loss or optical gain in the second waveguide. In this way, by controlling the bias applied to the second table, the optical loss induced in the second waveguide can be changed. In examples including both a first mesa and a second mesa, control of the bias voltage applied to each mesa provides for respectively modulating the optical gain and optical loss in each respective waveguide and fine tuning the gain-loss ratio.

[0060] In various embodiments, phase modulation can be used to tune the refractive index between waveguides, either alone or in combination with tuning the gain-loss ratio. For example, according to various examples of the disclosed technology, a hybrid MOSCAP can be provided relative to the waveguide, and a bias can be applied to the waveguide to modulate the phase of the optical mode of the corresponding waveguide. Phase modulation corresponds to an effective change in the refractive index of the waveguide. Therefore, the effective refractive index of the waveguide can be modulated by applying a voltage bias to the hybrid MOSCAP, thereby providing tuning of the refractive index difference between the waveguides. For example, the voltage bias applied to the MOSCAP provides phase tuning of the optical mode through a plasma dispersion effect or a carrier accumulation effect, thereby causing a change in phase. By tuning the refractive index difference, the examples provided herein can maintain a power extinction point to achieve PT symmetry and achieve efficient optical switching. That is, for lengths smaller than the possible length of a conventional directional coupler, optical switching depends only on the gain-loss ratio.

[0061] Fig. 6A and Figure 6B An example hybrid MOS optical modulator 600 that may be implemented in the techniques disclosed herein is illustrated. Fig. 6A is a top view of the light modulator 600, and Figure 6B is the edge of the optical modulator 600 Fig. 6A A cross-sectional view taken along the line AA' shown in FIG.

[0062] The optical modulator 600 includes an optical waveguide 602, a cathode 604 including a first material and formed in the optical waveguide 602, and an anode 606 including a second material different from the first material and formed in the optical waveguide 602. The anode is adjacent to the cathode. A capacitor is defined between the anode and the cathode.

[0063] In some examples, substrate 601 includes an oxide grown on bottom layer 608. Silicon layer 610 is formed on substrate 601. Grooves 612 divide optical modulator 600 into two parts 614 and 616. First part 614 includes anode 606. Optical waveguide 602 is formed in anode 606. Cathode 604 is integrated into second part 616. In various embodiments, cathode 604 includes a III-V material layer as a first material. MOS capacitor (MOSCAP) 624 is defined between cathode 604 and anode 606.

[0064] The dielectric 618 is formed between the cathode 604 and the anode 606. The dielectric 618 may be an electrically insulating material formed between the cathode 604 and the anode 606 of the MOSCAP 624, and for a given electric field strength, the polarization of the dielectric 618 may increase the surface charge of the MOSCAP 624 by applying an electric field. The dielectric 618 may be a native oxide of the cathode or anode or both, or may be an external dielectric material such as a high-k dielectric or polymer that may be formed by deposition, oxidation, wafer bonding, or other dielectric coating methods.

[0065] The cathode 604 may include a negatively doped III-V material, and the anode 606 may include positively doped silicon, other IV materials, or any semiconductor material capable of conducting electricity and transmitting light. A cathode electrode 620 is disposed on the cathode 604, and an anode electrode 622 is disposed on the anode 606. When a voltage is applied between the electrodes, carrier accumulation, depletion, or inversion may occur around the dielectric 618. Since the capacitor region overlaps the optical waveguide, changes in carrier concentration may result in changes in the refractive index and propagation loss of the waveguide mode. By biasing the voltage applied between the electrodes, the refractive index may be modulated accordingly, thereby causing light intensity modulation, phase shift modulation, and attenuation.

[0066] Light may be input into the optical modulator 600 via the waveguide 602. When the light propagates through the waveguide 602, the light may be modulated, attenuated, and phase-shifted based on a change in the waveguide mode refractive index caused by applying a bias voltage to the MOSCAP 624. The modulated light is then output from the optical modulator 600. For example, when a voltage is applied to an electrode, the waveguide mode refractive index may be changed by induced carrier accumulation, depletion, or inversion.

[0067] For example, Figure 6B A DC power supply 626 is included. The DC power supply 626 acts as a signal source and has a negative terminal connected to the cathode electrode 620 and a positive terminal connected to the anode electrode 622. This causes negative charge to migrate from the cathode 604 to the side of the optical waveguide 602 adjacent to the cathode 604, and positive charge ("holes") to migrate from the anode 606 to the opposite side of the waveguide 602 (also referred to herein as an accumulation mode). In other examples, the polarity of the DC power supply 626 can be reversed. Reversing the polarity of the DC power supply 626 causes negative charge to migrate from the waveguide 602 to the cathode electrode 620, and holes to migrate from the waveguide 602 to the anode electrode 622 (also referred to herein as a depletion mode).

[0068] MOSCAP 624 is formed at the boundary between the III-V material of cathode 604 and the underlying capacitor portion of intrinsic silicon or other IV material of anode 606. A thin layer of silicon and III-V oxide (e.g., dielectric 618) is naturally formed at the boundary and serves as the dielectric of the capacitor. In some examples, the thin layer has a nanometer-scale thickness, for example, a few nanometers thick. In some examples, no steps need to be taken to promote the formation of dielectric 618. In other examples, the formation of dielectric 618 can be stimulated, for example, by increasing the temperature, exposing the material to an oxygen-rich atmosphere, or other suitable techniques.

[0069] In some examples, the III-V material may include gallium arsenide (GaAS). In other examples, the III-V material may include indium phosphide (InP) or other compounds of indium, gallium, phosphorus, and arsenic. More generally, the cathode and anode are formed of different materials, which may include II-VI semiconductor compounds or other materials. Metals may be used.

[0070] In some examples, the III-V oxide forming dielectric 618 may include aluminum oxide (Al 2 O 3 ), hafnium oxide (HfO 2 ) or vanadium dioxide (VO 2 ). In other examples, the III-V oxides may include, but are not limited to, the compounds shown in Table 1 below (note that the gap of Si is 1.1 eV):

[0071] Table 1

[0072]

[0073] As previously discussed, MOSCAP 624 is formed inside optical waveguide 602 such that charge carriers accumulated / depleted on either side of the capacitor dielectric have the effect of changing the refractive index of the optical waveguide and changing waveguide losses (e.g., loss or attenuation of propagating signal power in a waveguide).

[0074] MOSCAP 624 can operate in accumulation, depletion, or inversion mode (e.g., there is an accumulation of electrons at the dielectric layer in addition to the presence of holes). As discussed above, a DC voltage can be applied between anode 606 and cathode 604, causing a thin charge layer to accumulate, deplete, or invert on both sides of dielectric layer 618. The resulting change in free carrier density results in a plasma or carrier accumulation effect, which results in a phase change in the optical mode of optical waveguide 602. This phase change manifests as a change in the effective refractive index of the optical mode (Δn eff The change or modulation of the effective refractive index (Δn eff) and the associated optical loss variation (Δα) can be described as follows:

[0075]

[0076] Where q is the charge applied to the cathode 604 and anode 606, c is the speed of light in a vacuum, and ε 0 is the dielectric constant of free space, n is the refractive index of the material, ΔN represents the change in carrier density, ΔN e represents the change in carrier density in terms of electrons, ΔNh represents the change in carrier density in terms of holes, and m* represents the change in electrons (m* ce ) and holes (m* ch )'s relative effective mass, μ h represents the hole mobility, μ e represents the electron mobility, and λ 0 is the free space wavelength.

[0077] Optical phase shift at the capacitor ends Depends on the voltage-induced Δn eff The amplitude of , the device length L and the optical wavelength λ. In this example, the optical phase shift can be calculated as Therefore, the optical phase of the light in the optical waveguide 602 can be determined based on the voltage-induced Δn eff In various examples, the waveguide loss in silicon and III-V materials can also change simultaneously with the change in carrier density, and the control of the change in waveguide loss can be used as an optical attenuator. For example, the change in waveguide loss can be controlled based on the change in carrier density, which can result in an attenuation of the waveguide loss. The attenuated waveguide loss can be used to modulate the signal.

[0078] Fig. 7A and Figure 7B shows that at various gap thicknesses, the Fig. 6A and Figure 6B The voltage of the optical modulator 600 is related to the refractive index change (Δn eff ) (left axis) and the free carrier absorption (FCA) loss variation (right axis). Fig. 7A and Figure 7B In the simulation, the cathode 604 is doped to 3×10 18 cm -2 The anode 606 is formed by n-doped gallium arsenide (GaAS), and the anode 606 is doped to 5×10 16 cm -2 Formed by p-doped silicon. Fig. 7A The simulated dielectric 618 is made of aluminum oxide (Al 2 O 3 ) is formed, and Figure 7B The simulated dielectric 618 is composed of hafnium oxide (HfO 2 ) is formed. Fig. 7A Figure 705 and Figure 7B As shown in the legend 715 of FIG. 715 , in each simulation, the gap thickness between the anode 606 and the cathode 604 (eg, the thickness of the dielectric 618 formed therebetween) was varied from 5 nm to 25 nm in increments of 5 nm. These are merely used to generate Fig. 7A and Figure 7B 0047] An example configuration of simulated data is shown in 0047. Other configurations may be considered in the embodiments disclosed herein.

[0079] like Fig. 7A Pointer 701 and Figure 7B The solid line shows the refractive index variation (Δn) of each gap thickness as a function of the voltage bias applied to the optical modulator 600, as indicated by the pointer 711 in FIG. eff ). Similarly, the dashed lines indicated by pointers 703 and 713 show the variation of the FCA loss for each gap thickness as a function of the voltage bias applied to the optical modulator 600. Fig. 7A and Figure 7B As shown, the amount of change in refractive index depends on the type of dielectric 618 and the gap thickness, and more particularly, as the gap thickness increases, the change in refractive index decreases. Fig. 7A and Figure 7B It is depicted that the amount of FCA losses depends on the type of dielectric 618 and the gap thickness, and more particularly, as the gap thickness increases, the FCA losses decrease.

[0080] FIG. 8A to FIG. 8C An example of a directional coupler according to embodiments disclosed herein is illustrated. Fig. 8A A top view of the directional coupler 800 is shown. Figure 8B The example directional coupler 800a is shown along Fig. 8A A cross-sectional view taken along line BB' within the coupling region. Figure 8C Another example directional coupler 800b is shown. Fig. 8A A cross-sectional view taken along line BB'. Figure 8B The directional coupler 800a of 8C and the directional coupler 800b of 8C are substantially the same as the directional coupler 800, except that the directional coupler 800a includes the isolation region 838 implemented as an ion region 838a and the directional coupler 800b includes the isolation region 838 implemented as a gap 838b (such as an air gap). Therefore, the following disclosure is also applicable to FIG. 8A to FIG. 8C Each of the , unless otherwise stated herein.

[0081] In various examples, the directional coupler 800 includes a buried oxide (BOX) layer 832, such as a silicon dioxide layer, grown on a substrate 834. The directional coupler 800 also includes a first portion 801 (also referred to herein as a first leg) and a second portion 802 (also referred to herein as a second leg) formed on the BOX layer 832. The first portion 810 is separated from the second portion 820 via a gap 836 (e.g., an air gap). The first portion 801 includes a first optical waveguide 803, and the second portion 802 includes a second optical waveguide 804. Each optical waveguide 803 and 804 has a corresponding one or more optical modes, and examples of the one or more modes of light energy are shown as regions 805 and 806, respectively. In various embodiments, the first waveguide 803 and the second waveguide 804 are single-mode waveguides.

[0082] The first optical waveguide 803 and the second optical waveguide 800 may be similar to Figure 1 The first waveguide 110 and the second waveguide 120. For example, the first optical waveguide 803 includes an input port and an output port, and the second optical waveguide 804 includes an input port and an output port. Figures 1 to 4C As described, light input into one waveguide can be tapped into another waveguide via gap 836. Fig. 8A In the illustrative example shown, light is input to the input port of the second optical waveguide 804 and output from the output ports of the two optical waveguides 803 and 804. Light input into one waveguide (e.g., one of the optical waveguides 803 and / or 804) can be transmitted across the gap 836 and the BOX layer 832 to another waveguide (e.g., one of the optical waveguides 804 and / or 803) and output from the directional coupler 800 for downstream use. The BOX layer 832 can be provided to confine the optical mode in the vertical direction (e.g., confined in a layer provided on the BOX layer 832). Controlling the width of the gap 836 can change the coupling ratio between the first optical waveguide 803 and the second optical waveguide 804 (e.g., a larger width results in a smaller coupling ratio).

[0083] The first portion 801 also includes a first table 821 and a first MOSCAP 811. The first table 821 is provided for introducing optical gain or optical loss into the first optical waveguide 803 based on applying a voltage bias between a contact electrode 823 (referred to herein as electrode 823) and a contact electrode 817 (referred to herein as electrode 817). Whether optical gain or optical loss is introduced is based on the polarity of the bias, for example, a forward bias can be used to introduce gain, while a reverse bias can be used to introduce loss. The first MOSCAP 811 is configured to change the refractive index of the first optical waveguide 803 based on a voltage bias between a contact electrode 819 (referred to herein as electrode 819) and electrode 817. For example, as described above, depending on the bias polarity, the voltage bias applied to the MOSCAP 811 provides phase tuning through a plasma dispersion effect or a carrier accumulation effect. The carrier accumulation effect via a positive voltage bias or forward voltage bias will change the phase and reduce the effective refractive index of the first waveguide 803, while the plasma dispersion effect via a negative voltage bias or reverse voltage bias will increase the effective refractive index. Further details on the components of the first mesa 821 and the first MOSCAP 811 are provided below.

[0084] The second portion 802 also includes a second mesa 822 and a second MOSCAP 812. The second mesa 822 is provided for introducing optical loss or optical gain into the second optical waveguide 804 based on applying a voltage bias (e.g., a reverse bias or a forward bias) between a contact electrode 824 (referred to herein as electrode 824) and a contact electrode 818 (referred to herein as electrode 818). Similar to the first MOSCAP 811, the second MOSCAP 812 is configured to change the refractive index of the second optical waveguide 804 based on a voltage bias between a contact electrode 820 (referred to herein as electrode 820) and the electrode 818. Further details on the components of the second mesa 822 and the second MOSCAP 812 are provided below.

[0085] Thus, the directional coupler 800 provides modulated gain and / or loss while tuning the refractive index difference between the first optical waveguide 803 and the second optical waveguide 804 so as to optimize the gain-loss ratio and power extinction, thereby obtaining a PT-symmetric directional coupler. For example, one or more voltage biases may be applied to the first table 821 and / or the second table 821 to individually tune the optical gain and / or optical loss so as to optimize the gain-loss ratio relative to the exceptional point. For example, a voltage bias may be applied to the first table 821 to modulate the gain or loss depending on the polarity of the bias (e.g., forward bias or reverse bias). Separately, a voltage bias may be applied to the second table 822 to modulate the loss or gain depending on the polarity of the bias (e.g., reverse bias or forward bias) while, after, or before the first table 821 is biased.

[0086] In some examples, a voltage bias consistent with the bias of the first mesa 821 and / or the second mesa 822 may be applied to the first MOSCAP 811 and / or the second MOSCAP 812 to tune the refractive index difference between the optical waveguide 803 and the optical waveguide 804. For example, applying a voltage to either the first MOSCAP 811 or the second MOSCAP 822 may cause a change in the refractive index of the corresponding optical waveguides 803 and 804 (e.g., according to Equations 6 and 7 above). The change in the refractive index of either or both of the first optical waveguide 803 and the second optical waveguide 804 may be used to tune the refractive index difference to maximize power extinction while optimizing the gain-loss ratio.

[0087] Although this article refers to FIG. 8A to FIG. 8C The examples provided provide both gain tuning and loss tuning, but the technology disclosed herein is not limited thereto. For example, an embodiment including one of the mesas 821 and 822 instead of including both the first mesas 821 and the second mesas 822 may be provided. For example, in one embodiment, the first mesas 821 may be provided without including the second mesas 822. Thus, as described above, the first mesas 821 may be biased to modulate the gain while the loss remains constant. As another example, the second mesas 822 may be provided without including the first mesas 821. In this case, the first mesas 821 may be biased to modulate the loss while the gain remains constant.

[0088] Similarly, although this article refers to Fig. 8A and Figure 8B The example provided provides two MOSCAPs for independently modulating the refractive index of each waveguide, but the technology disclosed herein is not limited to this. For example, an embodiment including one of MOSCAPs 811 and 812 instead of including both the first MOSCAP 811 and the second MOSCAP 812 may be provided. For example, in one embodiment, a first MOSCAP 811 may be provided without including the second MOSCAP 812. Therefore, as described above, the first MOSCAP 811 may be biased to modulate the refractive index of the first optical waveguide 803, while the refractive index of the second optical waveguide 804 remains unchanged. As another example, a second MOSCAP 812 may be provided without including the first MOSCAP 811. In this case, the second MOSCAP 812 may be biased to modulate the refractive index of the second optical waveguide 804, while the refractive index of the first optical waveguide 803 remains unchanged.

[0089] Turning now to the first portion 801 in more detail, the first portion 801 includes a cathode 807 including a first material and a portion of which is formed in the first optical waveguide 803, and an anode 809 including a second material different from the first material and also formed in the first optical waveguide 803. In some embodiments, the cathode 807 tapers to the waveguide at the input and output of the waveguide 803 to achieve an optical transition from the waveguide to the cathode 807, such as Fig. 8A The anode 809 is adjacent to the cathode 807 within the first optical waveguide 803. The first capacitor 811 is defined between the anode 809 and the cathode 807. In various embodiments, the cathode 807 includes a stepped cross-sectional shape to reduce the presence of the first material in areas that are not necessary to perform the function and operation of the first portion 801.

[0090] The anode 809 is formed on the BOX layer 832, and the cathode 807 is formed above the anode 809 opposite to the BOX layer 832. The anode 809 includes a groove 813 formed therein, and the cathode 807 spans the groove 813. The groove 813 can be provided to confine the optical mode in the horizontal direction. In various embodiments, the cathode 807 includes a III-V group material layer as a first material, such as indium phosphide (InP), gallium arsenide (GaAs) or other compounds of indium, gallium, phosphorus and arsenic. The cathode 807 can be formed by, for example, but not limited to, deposition, wafer bonding, monolithic growth or other manufacturing techniques. The anode 809 can include silicon or another IV group material as a second material, for example, germanium, silicon carbide, silicon germanium, etc. The capacitor 811 can be a first MOSCAP defined between the cathode 807 and the anode 809.

[0091] A dielectric 815 (also referred to herein as an interface layer) is formed between the cathode 807 and the anode 809 and is formed in the first optical waveguide 803. The dielectric 815 can be a native oxide of the cathode or anode or both, or an external dielectric material such as a high-k dielectric or polymer that can be formed by deposition, oxidation, wafer bonding, or other dielectric coating methods. For example, the dielectric 815 can be similar to Fig. 6A and Figure 6B The dielectric 618 may include aluminum oxide (Al 2 O 3 ), hafnium oxide (HfO 2 ), vanadium dioxide (VO 2 ) or any compound listed in Table 1.

[0092] The first MOSCAP 811 is formed at the boundary between the first material of the cathode 807 and the first optical waveguide 803 of the underlying semiconductor material (e.g., silicon or other Group IV material). A thin layer of silicon and a Group III-V oxide is formed at the boundary and serves as the dielectric of the capacitor (e.g., dielectric 815). In some examples, the dielectric layer 815 can have a nanometer-scale thickness, for example, the dielectric layer 815 can be a few nanometers thick. For example, as FIG. 7A to FIG. 7B As shown, the thickness of dielectric layer 815 can be between 5 nm and 25 nm. Fig. 7A and Figure 7B As described, for a smaller applied voltage bias, a smaller thickness means a larger change in the effective refractive index; however, a smaller thickness also means a larger FCA loss. Therefore, some embodiments utilize a dielectric with a smaller thickness (e.g., about 5 nm) and use gain / loss modulation through the first mesa 821 to address FCA losses. In some examples, no steps need to be taken to promote the formation of the dielectric 815. In other examples, the formation of the dielectric 815 can be stimulated, for example, by increasing the temperature, exposing the material to an oxygen-rich atmosphere, or other suitable techniques.

[0093] Electrode 817 is disposed on cathode 807, and electrode 819 is disposed on anode 809. When a voltage bias is applied to electrodes 817 and 819, carrier accumulation or depletion may occur around dielectric layer 815, as described in more detail below, based on the polarity of the voltage bias (e.g., forward bias or reverse bias, respectively), resulting in carrier or plasma dispersion effects. Since the capacitor region overlaps the optical waveguide, carrier concentration changes may result in changes in optical mode phase, effective refractive index, and propagation loss, for example, as explained in conjunction with equations 6 and 7. By biasing the voltage applied between electrode 817 and electrode 819, the refractive index may be modulated accordingly. For example, a voltage bias (e.g., a DC voltage bias) may be applied between anode 809 and cathode 807, such that a thin charge layer accumulates or depletes on both sides of dielectric layer 815. The resulting change in free carrier density results in a plasma or carrier accumulation effect, resulting in a phase change in the optical mode of the first optical waveguide 803. This phase change manifests itself as a change in the effective refractive index of the optical mode (Δn eff The change or modulation of the effective refractive index (Δn eff ) and the associated optical loss variation (Δα) can be described as set forth in Equations 6 and 7 above.

[0094] The cathode 807 may include a negatively doped material (e.g., an n-doped semiconductor layer including silicon or other Group IV materials), and the anode 809 may include a first portion 809a including a positively doped material (e.g., a p-doped semiconductor layer). In order to enhance the change of the effective refractive index and the optical phase shift induced in the first optical waveguide 803, the anode 809 includes a second portion 809b formed on the BOX layer 832, the second portion being adjacent to the first portion 809a opposite to the first optical waveguide 803. The electrode 819 may be disposed on the second portion 809b.

[0095] In various embodiments, the cathode 807 includes a heavily negatively doped material, the first portion 809a includes a positively doped material, and the second portion includes a heavily positively doped material. As used herein, heavily doped and lightly doped refer to the doping concentration relative to the doping material. That is, the heavily doped material includes a doping concentration (e.g., carrier concentration, holes or electrons, depending on whether the doping is p-type or n-type, respectively) greater than the doping material, while the lightly doped material includes a doping concentration less than the doping concentration of the doping material. In various examples disclosed herein, light doping can refer to a situation where the dopant concentration is approximately one atom per 100 million material atoms. Heavily doping can refer to a situation where the dopant concentration is much higher, such as approximately one atom per ten thousand material atoms. In an illustrative example, the cathode 807 can include a material having approximately 1e 18 cm -3 or higher n-type doping concentration of III-V materials. In another example, cathode 807 can be doped to about 1e 18 cm -3 With about 1e 19 cm -3 In an example, the first portion 809a may include a portion having approximately 1e 16 cm -3 and about 5e 18 cm -3 In some examples, the second portion 809b may include silicon or other Group IV materials that are heavily positively doped to, for example, greater than about 5e 18 cm -3 Other Group IV materials.

[0096] As described above, the first portion 801 also includes a first mesa 821, which is configured to cause optical gain and / or optical loss. For example, optical gain can be achieved by light emission generated in the first mesa 821, which generates light that can be absorbed in the optical energy region 805 and injected into the first optical waveguide 803. The light injected into the first optical waveguide 803 serves as optical gain introduced into the first optical waveguide 803. For example, light emission can be achieved by a light emitting diode, a laser diode, etc.

[0097] Alternatively, light loss can be achieved by light absorption in the first mesa 821 by absorbing light energy from the light energy region 805, thereby absorbing light propagating in the first optical waveguide 803. The reverse bias on the active region causes the electron-hole band to bend, thereby causing absorption. The light absorption from the second optical waveguide 804 corresponds to the propagation loss caused in the second optical waveguide 804. For example, light absorption can be achieved by applying a bias to the optically active medium.

[0098] To achieve modulation of optical gain or optical loss, the first mesa 821 includes an optically active region 825 (or a laser gain material in the case of a laser diode) formed on the cathode 807. The optically active region 825 may include, for example, a quantum dot (QD), a quantum well (QW), a quantum short wire (QD) structure, or any structure that can act as an optical gain medium to produce a carrier population inversion for optical gain. A semiconductor layer 827 is formed on the optically active region 825. The semiconductor layer 827 may include a positively doped III-V material, such as GaAs, etc. In an illustrative example, the semiconductor layer 827 may be doped with a p-type dopant to a value greater than about 5e 18 cm -3 concentration.

[0099] The electrode 823 may be formed on the semiconductor layer 827 opposite to the optically active region 825. In one example, when a forward voltage bias is applied between the electrode 823 and the electrode 817, stimulated emission in the optically active material 825 is caused by a cumulative carrier concentration change, thereby generating light. The generated light passes through these layers, is absorbed in the optical energy region 805, and is received at the first optical waveguide 803 and propagates therein. In another example, in response to a reverse voltage bias applied between the electrode 823 and the electrode 817, electron-hole band bending that causes absorption occurs, thereby absorbing the light propagating in the first optical waveguide 803 to cause propagation loss.

[0100] Thus, by biasing the voltage applied between the electrode 823 and the electrode 817, optical gain or optical loss can be added to the first optical waveguide 803 via the first mesa 821. The amount of optical gain or optical loss can be modulated based on changing the amplitude of the voltage bias applied to the first mesa 821, which can be tuned to reach the exceptional point according to the loss or gain in the second portion 802. In addition, by controlling the bias applied to the electrodes 823 and 817 and the bias applied to the electrodes 819 and 817, the optical gain-loss ratio can be tuned while tuning the refractive index difference between the first portion 801 and the second portion 802. Thus, while a change in gain can also cause a change in refractive index (and vice versa), both the refractive index and the gain-loss ratio can be tuned to ensure that power extinction is maintained and the gain-loss ratio is at or above the exceptional point.

[0101] The first mesa 821 also includes an ion region 829 within the semiconductor layer 827. The ion region 829 provides efficient electrical carrier confinement within the semiconductor layer 827. For example, in the case of induced optical gain, the ion region 829 limits carrier migration to a region vertically overlapping the first optical waveguide 803. Thus, the ion region 829 ensures that optical gain is generated toward the first optical waveguide 803, and in the horizontal direction, optical gain is not provided to the first optical waveguide 803. The ion region 829 can be formed by an ion implantation process for implanting ions into a portion of the semiconductor layer 827. The ions can be hydrogen ions (H 2 O 2 ) as desired for a given application. + ) or any other ions.

[0102] Now turn to the second portion 802 in more detail. The second portion 802 can be substantially similar to the first portion 801, with both having mirror-image structures. For example, the second portion 802 includes a cathode 808 that includes a first material and a portion of which is formed in the second optical waveguide 804. The second portion 802 also includes an anode 810 that includes a second material different from the first material and is also formed in the second optical waveguide 804. In some embodiments, the cathode 808 tapers to the waveguide at the input and output of the waveguide 804 to achieve an optical transition from the waveguide to the cathode 808, such as Fig. 8A 804. The anode 810 is adjacent to the cathode 808 within the second optical waveguide 804. The second capacitor 812 is defined between the anode 810 and the cathode 808. In various embodiments, the cathode 808 includes a stepped cross-sectional shape to reduce the presence of the first material in areas that are not necessary to perform the function and operation of the second portion 802.

[0103] The anode 810 is formed on the BOX layer 832, and the cathode 808 is formed above the anode 810 opposite to the BOX layer 832. The anode 810 includes a groove 814 formed therein, and the cathode 808 spans the groove 814. The groove 814 can limit the optical mode in the horizontal direction. In various embodiments, the cathode 808 includes a III-V material layer as a first material. The cathode 808 can be formed by, for example, but not limited to, deposition, wafer bonding, monolithic growth or other manufacturing techniques. The anode 810 may include silicon or another IV material as a second material. The capacitor 812 may be a second MOSCAP defined between the cathode 808 and the anode 810.

[0104] A dielectric 816 (also referred to herein as an interface layer) is formed between the cathode 808 and the anode 810 and in the second optical waveguide 804. The dielectric 816 can be a native oxide of the cathode or anode or both, or an external dielectric material such as a high-k dielectric or polymer that can be formed by deposition, oxidation, wafer bonding, or other dielectric coating methods. For example, the dielectric 816 can be similar to Fig. 6A and Figure 6B The dielectric 618 may include aluminum oxide (Al 2 O 3 ), hafnium oxide (HfO 2 ), vanadium dioxide (VO 2 ) or any compound listed in Table 1.

[0105] The second MOSCAP 812 is formed at the boundary between the first material of the cathode 808 and the underlying second optical waveguide 804. A thin layer of silicon and a III-V oxide is formed at the boundary and serves as a dielectric (e.g., dielectric 816) for the capacitor. In some examples, the dielectric layer 816 can have a nanometer-scale thickness, for example, the dielectric layer 816 can be a few nanometers thick. For example, as FIG. 7A to FIG. 7B As shown, the thickness of dielectric layer 816 can be between 5 nm and 25 nm. Fig. 7A and Figure 7B As described, for a smaller applied voltage bias, a smaller thickness means a larger change in the effective refractive index; however, a smaller thickness also means a larger FCA loss. Therefore, some embodiments utilize a dielectric with a smaller thickness (e.g., about 5 nm) and use gain / loss modulation through the second mesa 822 to address the FCA loss. In some examples, no steps need to be taken to promote the formation of the dielectric 816. In other examples, the formation of the dielectric 816 can be stimulated, for example, by increasing the temperature, exposing the material to an oxygen-rich atmosphere, or other suitable techniques.

[0106] An electrode 818 is disposed on the cathode 808, and an electrode 820 is disposed on the anode 810. When a voltage bias is applied to the electrodes 818 and 820, carrier accumulation or depletion may occur around the dielectric layer 816 based on the polarity of the voltage bias (e.g., forward bias or reverse bias, respectively), for example, similar to that described above in conjunction with the first MOSCAP 811. The change in carrier concentration in the overlapping portion of the first MOSCAP 811 and the second optical waveguide 804 may result in a change in the waveguide refractive index and propagation loss, for example, as explained in conjunction with Equations 6 and 7, which may be used to modulate the refractive index of the second optical waveguide 804. For example, a voltage bias (e.g., a DC voltage bias) may be applied between the anode 810 and the cathode 808 such that a thin charge layer accumulates or is depleted on both sides of the dielectric layer 816. The change in the free carrier density results in a change in the effective refractive index (Δn ) of the optical mode. eff ), as explained above in Equation 6 and Equation 7 above.

[0107] The cathode 808 may include a negatively doped material (e.g., an n-doped semiconductor layer including silicon or other Group IV materials), and the anode 810 may include a first portion 810a including a positively doped material (e.g., a p-doped semiconductor layer). In order to enhance the change of the effective refractive index and the optical phase shift induced in the second optical waveguide 804, the anode 810 includes a second portion 810b formed on the BOX layer 832, the second portion being adjacent to the first portion 810a opposite to the second optical waveguide 804. The electrode 820 may be disposed on the second portion 810b.

[0108] In various embodiments, cathode 808 includes a heavily negatively doped material, first portion 810a includes a positively doped material, and second portion includes a heavily positively doped material. In an illustrative example, cathode 808 may include a material having approximately 1e 18 cm -3 or higher n-type doping concentration of III-V materials. In another example, cathode 808 can be doped to about 1e 18 cm -3 With about 1e 19 cm -3 In an example, the first portion 810a may include a portion having approximately 1e 16 cm -3 and about 5e 18 cm -3 In some examples, the second portion 810b may include silicon or other Group IV materials that are heavily positively doped to, for example, greater than about 5e 18 cm -3 Other Group IV materials.

[0109] As described above, the second portion 802 also includes a second mesa 822, which is configured to cause optical loss and / or optical gain similar to that described in conjunction with the first mesa 821. In order to achieve modulation of optical gain or optical loss, the second mesa 821 includes an optically active region 826 (or a laser gain material in the case of a laser diode) formed on the cathode 808. The optically active region 826 may include, for example, a QD or a QW as an optical gain medium. A semiconductor layer 828 is formed on the optically active region 826. The semiconductor layer 828 may include a positively doped III-V material, such as GaAs, etc. In an illustrative example, the semiconductor layer 828 may be doped with a p-type dopant to a value greater than about 5e 18 cm -3 concentration.

[0110] The electrode 824 may be formed on the semiconductor layer 828 opposite to the optically active region 826. In one example, in the case where a forward voltage bias is applied between the electrode 824 and the electrode 818, stimulated emission in the optically active material 826 is caused by accumulated carrier concentration changes, thereby generating light. The generated light passes through these layers, is absorbed in the optical energy region 806, and is received at the second optical waveguide 804 and propagates therein. In another example, in response to a reverse voltage bias applied between the electrode 824 and the electrode 818, a carrier concentration change occurring by depletion causes energy absorption, thereby absorbing the light propagating in the second optical waveguide 804 to cause propagation loss.

[0111] Thus, by biasing the voltage applied between the electrode 824 and the electrode 818, optical gain or optical loss can be added to the second optical waveguide 804 via the second mesa 822. The amount of optical gain or optical loss can be modulated based on changing the amplitude of the voltage bias applied to the second mesa 822, which can be tuned to reach the exceptional point based on the loss or gain in the second portion 801. In addition, by controlling the bias applied to the electrodes 824 and 818 and the bias applied to the electrodes 820 and 818, the optical gain-loss ratio can be tuned while tuning the refractive index difference between the first portion 801 and the second portion 802. Thus, while a change in gain can also cause a change in refractive index (and vice versa), both the refractive index and the gain-loss ratio can be tuned to ensure that power extinction is maintained and the gain-loss ratio is at or above the exceptional point.

[0112] The second mesa 822 also includes an ion region 830 within the semiconductor layer 828. The ion region 830 provides efficient electrical carrier confinement within the semiconductor layer 828. For example, in the case of induced optical gain, the ion region 830 limits carrier migration to a region vertically overlapping the second optical waveguide 804. Thus, the ion region 830 ensures that optical gain is generated toward the second optical waveguide 804, and in the horizontal direction, optical gain is not provided to the second optical waveguide 804. The ion region 830, similar to the ion region 829, can be formed by an ion implantation process for implanting ions into a portion of the semiconductor layer 828. The ions can be hydrogen ions (H 2 O 2 ) as desired for a given application. + ) or any other ions.

[0113] In various examples, the first portion 801 and the second portion 802 may be formed simultaneously. For example, the anode 810 and the anode 809 may be formed as a single anode layer by, for example, but not limited to, deposition, wafer bonding, monolithic growth, or other manufacturing techniques. The gap 836 may then be formed by a chemical dry or wet etching process to form separate anodes 809 and 810 from the anode layer. At the same time or in different steps, grooves 814 and 813 may be etched from the anode layer. Next, a cathode layer of a III-V material may be formed on the anodes 809 and 810 as a single cathode layer, for example, but not limited to, by deposition, wafer bonding, monolithic growth, or other manufacturing techniques. For example, an optically active layer may be formed on the cathode layer by wafer bonding a donor wafer that already has an active region. The active region on the donor wafer is grown by metal organic chemical vapor deposition or molecular beam epitaxy. Then, another III-V material layer may be formed on the optically active layer, for example, but not limited to, by deposition, wafer bonding, monolithic growth, or other manufacturing techniques.

[0114] Next, an isolation region 838 may be formed in the cathode layer, the optically active layer, and another III-V material layer to form the first mesa 821 and the second mesa 822 by electrically isolating the first mesa 821 and the second mesa 822 from each other. Figure 8B In the illustrative example of FIG. 8 , isolation region 838 may be an ion region 838a formed by an ion implantation process similar to that used to form ion regions 829 and 830 to implant ions between mesas 821 and 822. The ions may be hydrogen ions (H + ) or any other ions. As another example, Figure 8CAs shown, the isolation region 838 can be formed by an etching process to remove material from the cathode layer, the optically active layer, and another III-V material layer to form a gap or space 838b between the first mesa 821 and the second mesa 822. In this case, the gap 836 can be formed as part of forming the isolation region 838, for example, forming the gap 838b can include forming the gap 836. In either example, the gap 838b or the ion region 838a electrically isolates the first mesa 821 and the second mesa 822, while also forming separate cathodes 808 and 807, optically active regions 826 and 825, and semiconductor layers 828 and 827. Then, the electrodes 820, 818, 824, 823, 817, and 819 can be formed on the corresponding layers by, for example, but not limited to, deposition, wafer bonding, monolithic growth, or other manufacturing techniques, as shown. Figure 8B and Figure 8C shown.

[0115] In various embodiments, such as Figure 8B and Figure 8C As shown, dielectrics 815 and 816 can span gap 836. For example, dielectrics 815 and 816 can be a single layer spanning first portion 801 and second portion 802, as illustrated herein. A single dielectric layer can be disposed in gap 836 and cover the sides of anodes 810a and 808b.

[0116] Although certain materials are described as being negatively doped or positively doped, embodiments are not limited thereto, and polarity doping can be switched. For example, although the above examples describe cathode 807 as negatively doped and anode 809 and semiconductor layer 827 as positively doped, the polarity of each layer can be switched such that cathode 807 is positively doped, while anode 809 and semiconductor layer 827 can be negatively doped. Similarly, the polarity of cathode 808, anode 810, and semiconductor layer 828 can be switched such that cathode 808 is positively doped, while anode 810 and semiconductor layer 828 can be negatively doped.

[0117] Fig. 9 Illustrated is carrier concentration migration within an example directional coupler according to embodiments disclosed herein. Fig. 9 Shows FIG. 8A to FIG. 8C A directional coupler 800 having carrier concentration and power supply overlaid thereon.

[0118] exist Fig. 9In the illustrative example shown, multiple power supplies are provided. For example, in the first part 801, the first power supply 910 is electrically coupled between the electrode 817 and the electrode 819, and the second power supply 920 is electrically coupled between the electrode 817 and the electrode 823, so that the first power supply 910 and the second power supply 920 share a common ground. In the second part 802, the third power supply 930 is electrically coupled between the electrode 818 and the electrode 820, and the fourth power supply 940 is electrically coupled between the electrode 818 and the electrode 824, so that the third power supply 930 and the fourth power supply 940 share a common ground. Power supplies 910 and 920 can be DC power supplies having a negative terminal connected to the electrode 817 and a positive terminal connected to the electrodes 819 and 823, respectively. Power supplies 930 and 940 can also be DC power supplies having a positive terminal connected to the electrode 818 and a negative terminal connected to the electrodes 820 and 824, respectively. Each power supply 910-940 can be, for example, by a controller (for example, implemented as Fig.11 The computer system described in (described in) controls to apply voltage biases between corresponding electrodes. That is, a first bias can be applied between electrode 817 and electrode 819, a second bias can be applied between electrode 817 and electrode 823, a third bias can be applied between electrode 818 and electrode 820, and a fourth bias can be applied between electrode 818 and electrode 824. Each of the first bias to the fourth bias can be applied simultaneously or selectively as needed. Each voltage bias can be independently controlled across the corresponding electrodes as needed to modulate each connected component, for example, each bias can be applied simultaneously or sequentially.

[0119] When the first power supply 910 applies the first bias voltage as a forward bias voltage between the electrode 817 and the electrode 819, negative charges and holes are accumulated around the dielectric 815, and the first MOSCAP 811 of the portion 801 operates in an accumulation mode. Fig. 9 As shown, negative charges from cathode 807 are directed to light energy region 805 (which includes Figure 8B and Figure 8C In the embodiment, the first optical waveguide 803 (shown in FIG. 1 ) migrates to accumulate on the upper surface of the dielectric 815, while holes (positive charges) migrate from the anode 809 to the first optical waveguide 803 to accumulate on the lower surface of the dielectric 815. As described above, the accumulation of charges and the change in carrier concentration at the dielectric 815 result in a carrier accumulation effect, thereby changing the refractive index and propagation loss of the first optical waveguide 803.

[0120] When the third power supply 930 applies a third bias voltage as a reverse bias voltage between the electrode 818 and the electrode 820, the second MOSCAP 812 operates in a depletion mode, and the free carrier concentration around the dielectric 815 moves away from the dielectric layer 816 in the optical energy region 806. That is, the free carriers (positive free carriers or holes are shown as circles with "+", and negative free carriers or electrons are shown as circles with "-") migrate away from the optical energy region 806, leaving a higher percentage of fixed carriers (positive fixed carriers or holes are shown as boxes with "+", and negative fixed carriers or electrons are shown as boxes with "-"). For example, as Fig. 9 As shown, negative charges from the optical energy region 806 migrate toward the electrode 818 to deplete the free carrier concentration and increase the fixed carrier concentration at the upper surface of the dielectric 815. Similarly, holes migrate from the optical energy region 806 to the electrode 820 to deplete the free carrier concentration and increase the fixed carrier concentration at the lower surface of the dielectric 816. As described above, the depletion of charge and the change in carrier concentration at the dielectric 816 lead to a plasma dispersion effect, thereby changing the second optical waveguide 804 (for example, in the case of Figure 8B and Figure 8C The refractive index and propagation loss of the optical energy region 806 are shown.

[0121] Therefore, selective control of the first power source 910 and / or the third power source 930 provides for modulating the refractive index of the optical waveguide 803 and / or the optical waveguide 804, respectively. As described above, by modulating the refractive index of the optical waveguide 803 and / or the optical waveguide 804, the refractive index difference therebetween can be changed so as to tune the refractive index difference as desired. For example, tuning the refractive index difference enables addressing the attenuation of gain / loss in the system and maintaining power extinction to achieve PT symmetry, thereby obtaining a PT symmetric directional coupler.

[0122] When the second power supply 920 applies the second bias voltage as a forward bias voltage between the electrode 817 and the electrode 823, the first mesa 821 is used to introduce optical gain, and the control of the second bias voltage provides gain tuning via the first mesa 821. As an illustrative example, negative charges and holes are accumulated in the optically active region 825 of the first mesa 821, and the optically active region is used as a pump source that can provide optical gain. For example, negative charges from the cathode 807 migrate to the optically active region 825, and holes migrate to the optically active region 825 through the semiconductor layer 827. The accumulation of charges and holes in the optically active region 825 provides an energy transition state to produce stimulated emission, thereby generating optical gain in the optical energy region 805 where light can be emitted. The emitted light propagates through the cathode 807 into the first optical waveguide 803 within the optical energy region 805. Therefore, the optical gain introduced into the first optical waveguide 803 can be modulated by selectively controlling the second bias voltage. This modulation can be used to tune the gain-loss ratio of the directional coupler 800 to locate the exception point and obtain a PT-symmetric directional coupler.

[0123] When the fourth power supply 940 applies a fourth bias voltage as a reverse bias voltage between the electrode 818 and the electrode 824, the second table 822 is used to introduce optical loss, and the control of the fourth bias voltage provides loss tuning via the second table 822. As an illustrative example, free carriers (e.g., negative charges and holes) are depleted from the optically active region 826 of the second table 821, leaving an increased concentration of fixed carriers within the optically active region 826, which is used to bend the electron-hole band diagram, thereby causing the band gap energy to decrease and thus absorb higher energy light. This absorption of higher energy light provides optical loss. Therefore, when the fourth bias voltage is applied, the higher energy light propagating in the waveguide 804 is absorbed by the cathode 808. Therefore, the optical loss introduced into the second optical waveguide 804 can be modulated by selective control of the fourth bias voltage. This modulation can be used to tune the gain-loss ratio of the directional coupler 800 to locate the exception point and obtain a PT-symmetric directional coupler.

[0124] By combining the above Fig. 9 The controlled biasing of the directional coupler 800 described above can tune the refractive index difference to maximize the power extinction at the output of the first waveguide 803 and the second waveguide 804, while tuning the gain loss ratio to provide optical switching. FIG. 3A to FIG. 3C , the first MOSCAP 811 and the second MOSCAP 812 may be biased to tune the directional coupler 800 to Figure 3A At the same time, the first mesa 821 and the second mesa 822 can be tuned to provide switching between inputs. As an illustrative example, the first light is input into the first waveguide 803, the second light is input into the second waveguide 804, and the refractive index difference is such that Figure 3AThe condition of exists in the directional coupler 800. If it is desired to switch the first light output from the first waveguide 803 to the second light, the first mesa 821 and the second mesa 822 can be tuned as follows Figure 3A 870cm shown -1 The gain-loss ratio of the transmitted light intensity matrix T 11 is -50 dB, and the output power corresponds to substantially all of the second light input into the second waveguide 804. Alternatively, if it is desired that the second light output from the first waveguide 804 be switched to the second light, the gain loss ratio may be tuned as follows: Figure 3A 499cm shown -1 At this time, the transmitted light intensity matrix T 12 is −70 dB, and the output power corresponds to substantially all of the first light input into the first waveguide 803 .

[0125] Fig.10 is an example flow chart illustrating an example process for tuning a directional coupler according to an embodiment disclosed herein. In this example, the process may be implemented by one or more controllers (e.g., as described below). Fig.11 One or more computer systems 1100) are executed. Fig.10 The flowchart of can be stored as a set of instructions in a machine-readable storage medium, which, when executed by a processor, causes the processor to perform the flowchart. The process can be performed to tune a directional coupler, such as in combination with FIG. 8A to FIG. 9 A directional coupler 800 is described.

[0126] At block 1002, a first voltage bias is applied to a first MOSCAP. For example, the first MOSCAP may be a first MOSCAP 811 formed in the first optical waveguide 803. As described above, the first MOSCAP 811 may be formed between an anode 809 and a cathode 807 with a dielectric 815 therebetween. The first voltage bias may be applied by a power source, such as Fig. 9 A first power source 910 is provided.

[0127] At block 1004, the first refractive index of the first waveguide is modulated by adjusting the first voltage bias. As described above, the first refractive index changes based on the carrier concentration in the first MOSCAP in response to the first voltage bias. That is, for example, the first voltage bias can be adjusted via one or more controllers, and the carrier concentration at the dielectric layer 815 of the first MOSCAP 811 changes in response to the adjustment. Based on the change in the carrier concentration, the refractive index of the waveguide changes as set forth in Equations 6 and 7 above.

[0128] At block 1006, a second voltage bias is applied to a first mesa disposed on a first MOSCAP. For example, the first mesa may be a first mesa 821 disposed on a first MOSCAP 811. As described above, the first mesa 821 includes an optically active region 825 to which a bias may be applied to produce optical gain and / or optical loss based on the polarity of the bias. The second voltage bias may be applied by a power source, such as Fig. 9 A second power source 920 is provided.

[0129] At block 1008, the optical gain or optical loss caused by the first mesa in the first waveguide is modulated by adjusting the second voltage bias. As described above, the gain or loss changes in response to the second voltage bias based on the carrier concentration in the optically active region 825 of the first mesa 821. That is, for example, the second voltage bias can be adjusted via one or more controllers, and the carrier concentration within the optically active region 825 changes in response to the adjustment. Based on the change in carrier concentration, the gain or loss (depending on the polarity of the bias) changes as described above.

[0130] At block 1018, the gain-loss ratio and the refractive index difference between the first optical waveguide and the second optical waveguide are tuned based on modulating at least the first refractive index at block 1004 and modulating the optical gain or optical loss at block 1008. For example, modulating the first refractive index can be used to tune the refractive index difference between the first optical waveguide 803 and the second optical waveguide 804 to maintain power extinction. Simultaneously or sequentially before or after, the optical gain or optical loss can be modulated to tune the gain-loss ratio between the first optical waveguide 803 and the second optical waveguide 804 to locate or exceed the exception point. By tuning the gain-loss ratio and the refractive index difference, a PT-symmetric directional coupler can be obtained at block 1020, for example, where the gain-loss ratio is tuned to be equal to or exceed the exception point, while the refractive index difference is tuned to maintain power extinction.

[0131] Optionally, at block 1010, a third voltage bias may be applied to the second MOSCAP. For example, the second MOSCAP may be a second MOSCAP 812 formed in the second optical waveguide 804. As described above, the second MOSCAP 812 may be formed between the anode 810 and the cathode 808, with the dielectric 816 therebetween. The third voltage bias may be applied by a power source, such as Fig. 9 A third power source 930 is provided.

[0132] Optionally, at block 1012, the second refractive index of the second waveguide may be modulated by adjusting the third voltage bias. As described above, the second refractive index changes based on the carrier concentration in the second MOSCAP in response to the third voltage bias. That is, for example, the third voltage bias may be adjusted via one or more controllers, and the carrier concentration at the dielectric layer 816 of the second MOSCAP 812 changes in response to the adjustment. Based on the change in the carrier concentration, the refractive index of the second waveguide changes as described in Equations 6 and 7 above.

[0133] Optionally, at block 1014, a fourth voltage bias may be applied to a second mesa disposed on the second MOSCAP. For example, the second mesa may be a second mesa 822 disposed on the second MOSCAP 812 (and therefore disposed on the second optical waveguide 804). As described above, the second mesa 822 includes an optically active region 826 that may be biased to produce optical gain and / or optical loss based on the polarity of the bias. The fourth voltage bias may be applied by a power source, such as Fig. 9 The fourth source 940.

[0134] Optionally, at block 1016, the optical gain or optical loss caused by the second mesa in the second waveguide is modulated by adjusting the fourth voltage bias. As described above, the gain or loss changes in response to the fourth voltage bias based on the carrier concentration in the optically active region 826 of the second mesa 822. That is, for example, the fourth voltage bias can be adjusted via one or more controllers, and the carrier concentration within the optically active region 826 changes in response to the adjustment. Based on the change in carrier concentration, the gain or loss (depending on the polarity of the bias) changes as described above.

[0135] In the case of performing such a process, the operation of block 1018 may include the modulation of blocks 1016 and 1012. For example, at block 1018, modulation of the first refractive index and the second refractive index may be used to tune the refractive index difference between the first optical waveguide and the second optical waveguide. Additionally, at block 1018, modulation of the gain and loss via the first mesa 821 and the second mesa 822 provides tuning of the gain-loss ratio.

[0136] Fig.11A block diagram of an example computer system 1100 is depicted in which various embodiments described herein may be implemented. The computer system 1100 includes a bus 1102 or other communication mechanism for transmitting information, one or more hardware processors 1104 coupled to the bus 1102 for processing information. The hardware processor(s) 1104 may be, for example, one or more general purpose microprocessors. As described above, the computer system 1100 may be implemented to control the above-described power supplies (e.g., one or more of the power supplies 910, 920, 930, and / or 940).

[0137] The computer system 1100 also includes a main memory 1106, such as a random access memory (RAM), cache, and / or other dynamic storage device, coupled to the bus 1102 for storing information and instructions to be executed by the processor 1104. The main memory 1106 may also be used to store temporary variables or other intermediate information during the execution of instructions to be executed by the processor 1104. Such instructions, when stored in a storage medium accessible to the processor 1104, cause the computer system 1100 to become a special-purpose machine customized to perform the operations specified in the instructions.

[0138] The computer system 1100 further includes a read only memory (ROM) 1108 or other static storage device coupled to the bus 1102 for storing static information and instructions for the processor 1104. A storage device 1110, such as a magnetic disk, optical disk, or USB thumb drive (flash memory drive), is provided and coupled to the bus 1102 for storing information and instructions.

[0139] The computer system 1100 may be coupled to a display 1112, such as a liquid crystal display (LCD) (or touch screen), via the bus 1102 for displaying information to a computer user. An input device 1114, including alphanumeric and other keys, is coupled to the bus 1102 for communicating information and command selections to the processor 1104. Another type of user input device is a cursor control 1116, such as a mouse, trackball, or cursor direction keys, for communicating direction information and command selections to the processor 1104 and for controlling cursor movement on the display 1112. In some embodiments, the same direction information and command selections as with a cursor control may be implemented by receiving touches on a touch screen without a cursor.

[0140] The computing system 1100 may include a user interface module for implementing a GUI, which may be stored in a mass storage device as executable software code executed by the computing device(s). By way of example, this module and other modules may include components (such as software components, object-oriented software components, class components, and task components), processes, functions, properties, procedures, subroutines, program code segments, drivers, firmware, microcode, circuits, data, databases, data structures, tables, arrays, and variables.

[0141] Generally, the words "component", "engine", "system", "database", "data storage", etc. as used herein may refer to logic implemented in hardware or firmware, or to a software instruction set written in a programming language such as Java, C or C++, which may have entry points and exit points. Software components can be compiled and linked to executable programs, installed in dynamic link libraries, or written in interpretive programming languages ​​such as BASIC, Perl, or Python. It should be understood that software components can be called from other components or from themselves, and / or can be called in response to detected events or interrupts. Software components configured for execution on a computing device can be provided in a computer-readable medium, such as a compact disk, a digital video disk, a flash memory drive, a disk, or any other tangible medium, or can be provided as a digital download (and can be originally stored in a compressed format or an installable format that needs to be installed, decompressed or decrypted before execution). Such software code can be stored in part or in whole on a memory device of an executing computing device for execution by the computing device. Software instructions can be embedded in firmware such as an EPROM. It will be further understood that hardware components may include connected logic units such as gates and flip-flops, and / or may include programmable units such as programmable gate arrays or processors.

[0142] The computer system 1100 may implement the techniques described herein using custom hard-wired logic, one or more ASICs or FPGAs, firmware, and / or program logic that is combined with the computer system to make the computer system 1100 a special purpose machine or to program it as a special purpose machine. According to one embodiment, the techniques herein are performed by the computer system 1100 in response to the processor(s) 1104 executing one or more sequences of one or more instructions contained in the main memory 1106. Such instructions may be read into the main memory 1106 from another storage medium, such as the storage device 1110. Execution of the sequences of instructions contained in the main memory 1106 causes the processor(s) 1104 to perform the process steps described herein. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions.

[0143] As used herein, the term "non-transitory media" and similar terms refer to any medium that stores data and / or instructions that cause a machine to operate in a specific manner. Such non-transitory media may include non-volatile media and / or volatile media. Non-volatile media include, for example, optical disks or magnetic disks, such as storage device 1110. Volatile media include dynamic memory, such as main memory 1106. Common forms of non-transitory media include, for example, floppy disks, floppy disks, hard disks, solid-state drives, magnetic tapes or any other magnetic data storage media, CD-ROMs, any other optical data storage media, any physical media with a pattern of holes, RAM, PROMs and EPROMs, flash EPROMs, NVRAMs, any other memory chips or boxes, and networked versions of these media.

[0144] Non-transient media are distinct from transmission media but can be used in conjunction with transmission media. Transmission media participate in the transfer of information between non-transient media. For example, transmission media include coaxial cables, copper wire, and optical fiber, including the wires that comprise bus 1102. Transmission media can also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications.

[0145] Computer system 1100 also includes a communication interface 1118 coupled to bus 1102. Communication interface 1118 provides bidirectional data communication coupled to one or more network links, and the one or more network links are connected to one or more local networks. For example, communication interface 1118 can be an integrated services digital network (ISDN) card, a cable modem, a satellite modem, or a modem for providing data communication connection to a telephone line of a corresponding type. As another example, network interface 1118 can be a local area network (LAN) card for providing data communication connection with a compatible LAN (or a WAN component for communicating with a WAN). Wireless links can also be implemented. In any such implementation, communication interface 1118 sends and receives electrical signals, electromagnetic signals, or optical signals carrying digital data streams representing various types of information. Communication interface 1118 can be communicatively coupled to one or more power supplies (e.g., one or more power supplies in power supplies 450, 460, 550, 560, 650, and 660 of Figures 4 to 6).

[0146] A network link typically provides data communications to other data devices through one or more networks. For example, a network link can provide a connection through a local network to a host computer or to data devices operated by an Internet Service Provider (ISP). The ISP in turn provides data communications services through a global packet data communications network now commonly referred to as the "Internet". Both the local network and the Internet use electrical, electromagnetic, or optical signals that carry digital data streams. Signals through various networks and signals on the network link and through the communication interface 1118 (which carry digital data to and from the computer system 1100) are example forms of transmission media.

[0147] Computer system 1100 can send messages and receive data, including program code, through the network(s), network links and communications interface 1118. In the Internet example, a server can transmit the requested code for an application program through the Internet, an ISP, a local network and communications interface 1118.

[0148] The received code may be executed by the processor 1104 as it is received and / or stored in the storage device 1110, or other non-volatile memory, for later execution. Thus, the computer system 1100 may be configured to control the voltage bias applied between the contact electrodes by sending instructions to one or more power supplies via the communication interface(s) 1118 in accordance with instructions stored in the main memory 1106 and / or the ROM 1108.

[0149] Each process, method, and algorithm described in the previous sections can be implemented in a code component executed by one or more computer systems or computer processors including computer hardware and automated in whole or in part by these code components. The one or more computer systems or computer processors can also operate to support the carrying out of related operations in a "cloud computing" environment, or operate as "software as a service" (SaaS). These processes and algorithms can be implemented in part or in whole in a dedicated circuit. The various features and processes described above can be used independently of each other, or can be combined in various ways. Different combinations and sub-combinations are intended to fall within the scope of the present disclosure, and some method boxes or process boxes can be omitted in some embodiments. The methods and processes described herein are also not limited to any specific order, and the boxes or states related to these methods and processes can be carried out in other appropriate orders, or can be carried out in parallel, or in some other way. Boxes or states can be added to or removed from the disclosed example embodiments. The carrying out of certain operations or processes can be distributed to multiple computer systems or computer processors so that it does not reside only in a single machine, but is deployed across multiple machines.

[0150] As used herein, circuits can be implemented using any form of hardware, software or a combination thereof. For example, one or more processors, controllers, ASIC, PLA, PAL, CPLD, FPGA, logic components, software routines or other mechanisms can be implemented to form circuits. In an embodiment, the various circuits described herein can be implemented as discrete circuits, or the described functions and features can be shared partially or entirely among one or more circuits. Even if various features or functional elements can be described or advocated separately as separate circuits, these features and functions can also be shared between one or more common circuits, and this description should not require or imply that separate circuits are needed to implement such features or functions. In the case of using software to implement circuits in whole or in part, such software can be implemented to operate together with a computing system or processing system (such as computer system 1100) that can perform the functions described about the software.

[0151] As used herein, the term "or" may be interpreted in an inclusive or exclusive sense. Furthermore, descriptions of resources, operations, or structures in the singular should not be construed to exclude the plural. Unless expressly stated otherwise, or otherwise understood within the context as used, conditional language (such as, among others, "can," "could," "might," or "may") is generally intended to convey that certain embodiments include and other embodiments do not include certain features, elements, and / or steps.

[0152] Unless otherwise expressly stated, the terms and phrases used in this document and their variations should be interpreted as open-ended rather than restrictive. Adjectives such as "conventional", "traditional", "normal", "standard", "known" and terms of similar meaning should not be interpreted as limiting the items described to items available in a given time period or at a given time, but should be understood to include conventional, traditional, normal or standard technologies that may be available or known at any time now or in the future. In some cases, the presence of broad words and phrases such as "one or more", "at least", "but not limited to" or other similar phrases should not be understood to mean that narrower situations are intended or required where such broad phrases may not be present.

Claims

1. A directional coupler, comprising: A first silicon layer, wherein the first silicon layer is disposed above the buried oxide BOX layer, wherein the first silicon layer comprises: a first doping region, the first doping region having a first trench, a second doping region, wherein the second doping region has a second trench, a first gap region, the first gap region being disposed between the first doped region and the second doped region; a first oxide layer, the first oxide layer being disposed above the first doping region and the second doping region; A first mesa, wherein the first mesa is disposed on the first doped region of the first silicon layer, wherein the first mesa comprises: a first III-V family layer, the first III-V family layer being disposed above the first oxide layer; a first optically active region disposed over the first III-V family layer; and a second III-V family layer disposed over the first optically active region; and A second mesa, wherein the second mesa is disposed on the second doping region of the first silicon layer, wherein the second mesa comprises: a third III-V family layer, the third III-V family layer being disposed above the first oxide layer; a second optically active region disposed above the third III-V family layer; and A fourth III-V family layer is disposed above the second optically active region.

2. The directional coupler according to claim 1, wherein: The first oxide layer includes at least one of HfO2, Al2O3 and VO2.

3. The directional coupler according to claim 1, wherein: The first optically active region and the second optically active region are one of a quantum dot layer, a quantum well layer and a quantum short wire layer.

4. The directional coupler according to claim 1, wherein: The first III-V group layer, the second III-V group layer, the third III-V group layer, and the fourth III-V group layer include one of gallium arsenide and indium phosphide.

5. The directional coupler of claim 1, further comprising: a first waveguide disposed in a first doped region between the first trench and the gap region; as well as A second waveguide is disposed in a second doping region between the second trench and the gap region.

6. The directional coupler of claim 1, wherein: The second III-V family layer includes a first ion region, and The fourth III-V group layer includes a second ion region.

7. The directional coupler of claim 1, wherein: The gap area is disposed between the first table and the second table, and An isolation region is disposed on the first gap region between the first mesa and the second mesa.

8. The directional coupler of claim 7, wherein: The isolation region includes a third ion region.

9. The directional coupler of claim 7, wherein: The isolation region includes a second gap region.

10. The directional coupler of claim 1, wherein: The first doped region, the second doped region, the second III-V family layer, and the fourth III-V family layer are doped with a first polarity, and the first III-V family layer and the third III-V family layer are doped with a second polarity different from the first polarity.

11. The directional coupler of claim 10, wherein: The first polarity is a p-type, and the second polarity is an n-type.

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