Method and device for compensating temporal walk-off in quantum optical circuit

Abstract

A device for compensating temporal walk-off of a nonlinear quantum optical element according to the technical idea of the present disclosure includes an optical waveguide for propagating input light along a specific path. The optical waveguide includes: a nonlinear optical source section that transmits input light including a plurality of modes; a polarization separation section that separates the plurality of modes; a taper section that converts the separated modes; and a curve section that changes the direction of propagation of the input light. The plurality of modes include a pump wave, a signal wave, and an idler wave. The group velocities of the pump wave and the idler wave are identical, and the group velocity of the signal wave differs from that of the pump wave or the idler wave.

Description

Method and device for compensating temporal distance in quantum optical circuits

[0001] The present disclosure relates to a method for resolving temporal drift occurring in an optical waveguide of a quantum optical circuit, and more particularly, to a method and device for compensating for temporal drift by matching similar group velocities in a nonlinear optical process in which three or more optical modes participate.

[0002] Ultrafast nonlinear optical processes are of great importance not only for quantum technology applications such as quantum optical state generation and quantum frequency conversion, but also for classical optical applications such as second harmonic generation and optical parametric amplifiers. To increase the efficiency of this process, a method of pumping the medium more powerfully is typically used. However, the high power of pumping the medium causes various types of noise due to the secondary nonlinear effects that arise. This noise is particularly critical in quantum optical applications, limiting performance in various applications due to noise.

[0003] High optical power generates noise due to self-phase modulation, cross-phase modulation, two-photon absorption, and photorefractive effects, which lowers the performance indicators of nonlinear optical devices, causes reliability problems, and distorts the spectrum of optical modes in unpredictable ways, making it very difficult to control and design them.

[0004] Furthermore, being able to vary efficiency as desired is crucial for creating programmable quantum information processing devices. Typically, this is achieved by varying the pump power. However, because the impact of noise varies significantly depending on the pump power, the optical modes generated at different powers do not perfectly match each other. This mismatch is a source of errors in quantum information processing, and resolving it is a key challenge in generating optical quantum states.

[0005] That is, it is important to control the noise generated in the strong pumping region and to solve the noise problem for programmable quantum information processing devices.

[0006] To increase the efficiency of nonlinear optical processes while avoiding strong pumping, one strategy is to lengthen the medium length to allow longer interactions. However, this strategy is limited by the temporal separation of optical modes.

[0007]

[0008] *In ultrafast nonlinear optical processes, multiple optical modes propagate through a medium. Referring to Figure 1, the propagating optical modes generally have different group velocities, so they move apart as they traverse the medium. As these optical modes move apart, their spatial overlap decreases, limiting the efficiency and bandwidth of nonlinear optical phenomena. Because the temporal separation between modes increases as the medium length increases, the method of increasing the efficiency of nonlinear optical processes by lengthening the medium no longer works.

[0009] To address the temporal separation problem, a method has been proposed to compensate for the temporal separation by selectively delaying only the optical mode that propagates faster than the other optical modes after two optical modes have temporally separated. This method regroups the two optical modes that are moving apart due to different group velocities, making it appear as if the two modes have the same group velocities and are not moving apart. Therefore, this method is called quasi-group velocity matching.

[0010] Referring to Figure 2, in a pseudo-group velocity matching device, the mode with the faster group velocity among the two optical modes is transferred to a delay line by a directional coupler. After passing through this delay line, it returns from the delay line to the main line through a directional coupler. At this time, by carefully adjusting the length of the delay line, the two optical modes can converge at the same location without temporal separation.

[0011] However, extending this method to processes involving three or more optical modes requires the design of two or more delay lines and directional couplers, increasing implementation complexity. In particular, directional couplers are extremely difficult to design because they must selectively couple only the optical modes that need to be sent to the delay line among multiple optical modes, making designing multiple delay lines a significant burden. This is evident from the fact that the design and implementation of pseudo-group velocity matching in nonlinear optical processes involving three or more optical modes has never been reported.

[0012] Moreover, adding directional couplers and delay lines to the circuit incurs additional optical losses, thereby diminishing the high nonlinear optical efficiency achieved through pseudo-group velocity matching. For example, when quantum optical processes occur in nonlinear media, optical losses reduce the purity of the quantum squeezed state and hinder higher compression. Furthermore, in quantum frequency conversion, optical losses lower the conversion efficiency, which offsets the efficiency gains achieved through pseudo-group velocity matching.

[0013] The technical idea of ​​the present disclosure is to propose a method for implementing pseudo group velocity matching using only a number of delay lines less than n in an ultrafast nonlinear optical process in which n optical modes participate.

[0014] However, the problems to be solved in this disclosure are not limited to the problems mentioned above, and other problems not mentioned can be clearly understood based on the description below.

[0015] A device for compensating for temporal drift of a nonlinear quantum optical element according to the technical idea of ​​the present disclosure includes an optical waveguide for propagating input light along a specific path. The optical waveguide includes a nonlinear optical source section for transmitting input light including a plurality of modes, a polarization separation section for separating the plurality of modes, a taper section for converting the separated modes, and a curve section for changing the direction of propagation of the input light. The plurality of modes include a pump wave, a signal wave, and an idler wave. The group velocities of the pump wave and the idler wave are identical, and the group velocity of the signal wave is different from that of the pump wave or the idler wave.

[0016] Alternatively, the optical waveguide is characterized in that it is separated into a first waveguide and a second waveguide in the polarization separation section, the pump wave and the idler wave are transmitted to the first waveguide, and the signal wave is moved from the first waveguide to the second waveguide and transmitted.

[0017] Alternatively, the pump wave and the idler wave are characterized in that they are fundamental transverse magnetic mode (TM0) among transverse magnetic (TM) modes, and the signal wave is characterized in that they are fundamental transverse electric mode (TE0) among transverse electric (TE) modes.

[0018] Alternatively, the signal wave and the idler wave are characterized in that they are a first wavelength, and the pump wave is a second wavelength that is half of the first wavelength.

[0019] Alternatively, in the polarization separation section, the signal wave is characterized in that it is converted from the fundamental transverse electric mode (TE0) to the first transverse electric mode (TE1).

[0020] Alternatively, the polarization separation section includes a preparation region, a coupling region, and an escape region, wherein the coupling region is characterized in that it moves the signal wave from the first waveguide to the second waveguide based on adiabatic coupling.

[0021] Alternatively, the taper section is characterized by converting the signal wave from the primary transverse electric mode (TE1) to the fundamental transverse magnetic mode (TM0).

[0022] Alternatively, the first waveguide is characterized by including a first straight path set to a first length to control a delay time of the pump wave or idler wave in the taper section.

[0023] Alternatively, the curved section includes a first sub-section for rotating the path by a first angle, a second sub-section which is a straight path, and a third sub-section for rotating the path by a second angle, and in the first sub-section of the first waveguide, the pump wave is converted from a fundamental transverse magnetic mode (TM0) to a fundamental transverse electric mode (TE0), and the second sub-section of the first waveguide is characterized in that it is set to a second length so that the pump wave can return from the fundamental transverse electric mode (TE0) to the fundamental transverse magnetic mode (TM0).

[0024] A method for compensating for temporal drift of a nonlinear quantum optical element performed by a temporal drift compensation device according to the technical idea of ​​the present disclosure comprises the steps of transmitting input light including a pump wave, a signal wave, and an idler wave, transmitting the pump wave and the idler wave to a first waveguide, and separating the signal wave from the first waveguide to a second waveguide. The group velocities of the pump wave and the idler wave are identical, and the group velocity of the signal wave is different from that of the pump wave or the idler wave.

[0025] Alternatively, in the step of transmitting the input light, the pump wave and the idler wave are characterized in that they are fundamental transverse magnetic mode (TM0) among transverse magnetic (TM) modes, and the signal wave is characterized in that they are fundamental transverse electric mode (TE0) among transverse electric (TE) modes.

[0026] Alternatively, the sum of the frequency of the signal wave and the frequency of the idler wave is equal to the frequency of the pump wave.

[0027] Alternatively, the separating step is characterized by further comprising a step of converting the signal wave from a fundamental transverse electrical mode (TE0) to a first transverse electrical mode (TE1).

[0028] Alternatively, the method further comprises a step of converting the signal wave from a primary transverse electric mode (TE1) to a fundamental transverse magnetic mode (TM0) to reduce optical loss occurring as the signal wave passes through a curved path.

[0029] Alternatively, the method includes a step of changing the direction of propagation of input light in the first waveguide. The changing step includes a step of rotating the path of the input light by a first angle, a step of propagating the input light along a second straight path included in the first waveguide, and a step of rotating the path of the input light by a second angle. In the step of rotating the path by the first angle, the pump wave is converted from a fundamental transverse magnetic mode (TM0) to a fundamental transverse electric mode (TE0). The second straight path is characterized in that it is set to a second length so that the pump wave returns from the fundamental transverse electric mode (TE0) to the fundamental transverse magnetic mode (TM0).

[0030] According to the technical idea of ​​the present disclosure, the group velocity of an optical mode can be matched using a delay line, and the number of delay lines and directional couplers required for similar group velocity matching can be reduced.

[0031] The effects that can be obtained from the embodiments of the present disclosure are not limited to the effects mentioned above, and other effects not mentioned can be clearly derived and understood by those skilled in the art to which the embodiments of the present disclosure pertain from the following description. In other words, unintended effects resulting from practicing the embodiments of the present disclosure can also be derived from the embodiments of the present disclosure by those skilled in the art.

[0032] Figure 1 is a diagram showing two optical modes moving apart in time as they propagate through a medium.

[0033] Figure 2 is a diagram for explaining pseudo-group velocity matching in a nonlinear optical process in which two optical modes participate.

[0034] FIG. 3 is a block diagram showing a temporal distance compensation device in a quantum optical circuit according to an embodiment of the present disclosure.

[0035] FIG. 4 is a diagram showing a temporal distance compensation device in a quantum optical circuit according to an embodiment of the present disclosure.

[0036] FIG. 5 is a diagram illustrating a temporal distance compensation device in a quantum optical circuit according to an embodiment of the present disclosure.

[0037] FIG. 6 is a drawing for explaining a mode in a polarization separation section according to an embodiment of the present disclosure.

[0038] FIG. 7 is a diagram for explaining the length of a straight path in an Euler band according to an embodiment of the present disclosure.

[0039] FIG. 8 is a drawing illustrating the use of N connected temporal distance compensation devices in a quantum optical circuit according to an embodiment of the present disclosure.

[0040] FIG. 9 is a drawing illustrating the result of compensating for temporal distance through a temporal distance compensation device in a quantum optical circuit according to an embodiment of the present disclosure.

[0041] Below, embodiments of the present disclosure are described in detail with reference to the attached drawings so that those skilled in the art can easily implement the present disclosure. The embodiments presented in this disclosure are provided to enable those skilled in the art to utilize or implement the contents of the present disclosure. Accordingly, various modifications to the embodiments of the present disclosure will be apparent to those skilled in the art. That is, the present disclosure may be implemented in various different forms and is not limited to the embodiments described below.

[0042] Throughout the specification of this disclosure, identical or similar drawing numbers refer to identical or similar components. Furthermore, for the purpose of clearly describing the disclosure, drawing numbers for parts in the drawings that are not relevant to the description of the disclosure may be omitted.

[0043] The term "or" as used herein is intended to mean an inclusive "or" rather than an exclusive "or." That is, unless otherwise specified herein or clear from context, "X employs A or B" should be understood to mean either of the natural inclusive permutations. For example, unless otherwise specified herein or clear from context, "X employs A or B" can be interpreted to mean either X employs A, X employs B, or X employs both A and B.

[0044] The term "and / or" as used herein should be understood to refer to and include all possible combinations of one or more of the related concepts listed.

[0045] The terms "comprises" and / or "comprising" as used herein should be understood to mean the presence of certain features and / or components. However, it should be understood that the terms "comprises" and / or "comprising" do not exclude the presence or addition of one or more other features, other components, and / or combinations thereof.

[0046] Unless otherwise specified in this disclosure or unless the context makes it clear that the singular form is intended to be referred to, the singular should generally be construed to include “one or more.”

[0047] The term "Nth (N is a natural number)" used in this disclosure can be understood as an expression used to distinguish components of this disclosure from each other based on a predetermined standard such as a functional perspective, a structural perspective, or convenience of explanation. For example, components performing different functional roles in this disclosure can be distinguished as a first component or a second component. However, components that are substantially the same within the technical spirit of this disclosure but must be distinguished for convenience of explanation may also be distinguished as a first component or a second component.

[0048] As used herein, "temporal walk-off" refers to the phenomenon in which different optical modes gradually separate in the time domain while propagating. For example, even if two modes start propagating simultaneously at the same location, their group velocities vary depending on the characteristics of each mode, such as wavelength and effective refractive index, and the arrival times of the two modes may vary as the modes progress. Temporal walk-off is an important factor in determining the bandwidth of nonlinear interactions, and the bandwidth of the phase-matching function becomes narrower as the temporal walk-off increases. The "effective index" is the refractive index related to the propagation constant of each mode, and can be calculated or experimentally derived by considering the overall optical properties of a complex structure.

[0049] As used herein, the term "mode" refers to a specific electromagnetic field distribution pattern in which light can propagate within an optical waveguide. For example, the mode may include a transverse electric (TE) mode or a transverse magnetic (TM) mode. The modes may each include order information, such as TE0 and TE1. For example, the order may be the number of nodes of the optical mode, where a "node" may be a node of a transverse electric field of a transverse electric mode or a transverse magnetic field of a transverse magnetic mode. In the present disclosure, the transverse magnetic mode or transverse electric mode may be a quasi-transverse electric mode or a quasi-transverse magnetic mode (quasi-TE / TM). This is because the shape of the optical waveguide is not always symmetrical, so there is coupling between the TE / TM modes.

[0050] The "input light" used in the present disclosure is a concept including one or more waves or modes having various characteristics. In the present disclosure, three expressions are used: "pump wave," "signal wave," and "idler wave" that propagate in a waveguide. When "pump mode," "signal mode," and "idler mode" are used, the expression "mode" may be redundant and cause confusion, so the expression "wave" is used instead of mode. When describing the characteristics of the "pump wave," "signal wave," and "idler wave," for example, the "pump wave" is expressed as changing from the "fundamental transverse electric mode (TE0)" to the "first transverse electric mode (TE1)".

[0051] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the attached drawings.

[0052] FIG. 3 is a block diagram showing a temporal distance compensation device in a quantum optical circuit according to an embodiment of the present disclosure.

[0053] Referring to FIG. 3, the first temporal distance compensation device (100) may be connected to a plurality of temporal distance compensation devices of corresponding types. For example, as illustrated in FIG. 3, the first temporal distance compensation device (100) and the second temporal distance compensation device (100_2) may be connected and used. For convenience of explanation, a configuration in which n temporal distance compensation devices are connected is expressed as a temporal distance compensation system (10). Since the structure and operating principles of each temporal distance compensation device are the same, the description will be based on the first temporal distance compensation device (100).

[0054] The first temporal distance compensation device (100) or temporal distance compensation system (10) can move a wave with a fast group velocity (e.g., a signal wave) to a delay line to match the arrival time with other waves (e.g., a pump wave, an idler wave).

[0055] The first temporal distance compensation device (100) may include a nonlinear optical source 1 (140), a polarization separation section (110), a taper section 1 (120), and a curve section 1 (130).

[0056] Nonlinear optical source 1 (140) can convert and provide input light used in the first temporal distance compensation device (100) to have desired characteristics. For example, nonlinear optical source 1 (140) may include various materials such as periodically polarized materials such as PPLN (Periodically Poled Lithium Niobate) or PPKTP (Periodically Poled Potassium Titanyl Phosphate), semiconductor materials using quasi-phase matching (GaAs / AlGaAs multilayer structure), silicon nitride (Si3N4) waveguides, etc. In the present disclosure, for convenience of explanation, nonlinear optical source 1 (140) is described based on PPLN, but is not limited thereto and may include various nonlinear optical materials or configurations that perform the same role.

[0057] Nonlinear optical source 1 (140) can provide a pump wave, a signal wave, and an idler wave, and can set the group velocity of each wave in a desired form by considering the characteristics of the waveguide, the wavelength of each wave, the effective index, etc. For example, nonlinear optical source 1 (140) can provide a pump wave, a signal wave, and an idler wave by making the group velocity of the pump wave and the idler wave the same and setting the group velocity of the signal wave to be faster than the group velocity of the pump wave.

[0058] In the present disclosure, the sum of the energy (or frequency) of the signal wave and the idler wave can be set to be equal to the energy (or frequency) of the pump wave. For example, the frequencies of the signal wave and the idler wave may be equal, and the frequency of the pump wave may be twice the frequency of the signal wave or the idler wave.

[0059] In the present disclosure, the signal wave is separated by setting the pump wave and the idler wave to the transverse magnetic mode (TM0) and the signal wave to the transverse electric mode (TE0), but the present invention is not limited thereto. The signal wave may be separated by setting the pump wave and the idler wave to the transverse electric mode (TE0) and the signal wave to the transverse magnetic mode (TM0), or the waveguide may be designed to separate the signal wave based on different characteristics of each wave.

[0060] The polarization separation section (110) may be a mode selective adiabatic coupler (or APBS, adiabatic polarization beam splitter). By using an adiabatic coupler in the polarization separation section (110), the operating bandwidth can be increased and tolerance for process errors can be improved. In the present disclosure, the polarization separation section (110) is described based on an adiabatic coupler, but is not limited thereto, and an asymmetric Mach-Zehnder interferometer or various types of couplers can be utilized.

[0061] The polarization separation section (110) can separate only the signal wave among the pump wave, signal wave, and idler wave using a delay waveguide. The polarization separation section (110) can include a preparation region (not shown), a coupling region (not shown), and an escape region (not shown).

[0062] When the cross-sectional shapes of the nonlinear optical source 1 (140, or PPLN) and the polarization separation section (110) are different, optical loss due to mode mismatch may occur in the transmitted input light (or pump wave, signal wave, idler wave). To reduce such optical loss, a preparation region may be provided before the coupling region. From the preparation region, the optical waveguide may be separated into a first waveguide (primary waveguide) and a second waveguide (auxiliary waveguide). In the preparation region, the input light (or signal wave) is not transmitted to the second waveguide, but the shape of the cross-section can be gradually adjusted to match that of the coupling region through the preparation region.

[0063] In the coupling region, the input light (or signal wave) can move from the first waveguide to the second waveguide by the adiabatic coupling principle. For example, referring to Fig. 6 (a), mode coupling can occur in the section where mode 4 and mode 2 meet (P11) and then move away (P12). If this section (P11 to P12) is slowly passed, the input light (or signal wave) will continue to maintain mode 4, and through this, the input light (or signal wave) can move from the first waveguide to the second waveguide.

[0064] The escape region may be a region that gradually moves from the coupling region to a region where no coupling exists. The polarization separation region (110) and details of each region are described again in FIG. 5.

[0065] Taper section 1 (120) may be an adiabatic taper. Taper section 1 (120) can convert the mode of input light (e.g., signal wave). The signal wave, which is the primary transverse electric mode (TE1), may be susceptible to curve loss. Therefore, optical loss may be reduced by converting the signal wave into the fundamental transverse magnetic mode (TM0) in taper section 1 (120) before entering curve section 1 (130). Since the idler wave or pump wave may also experience increased curve loss in a wide-linewidth waveguide, taper section 1 (120) may be designed to reduce the linewidth of the waveguide. Taper section 1 (120) may include a straight path for controlling a delay time.

[0066] Curve section 1 (130) may be an Euler bend. In curve section 1 (130), the waveguide may be designed in a curved shape to rotate to change the direction of propagation of input light.

[0067] Due to the anisotropy of lithium niobate (LN), the effective refractive index changes when the propagation direction of the waveguide changes, and the effective refractive indices of the fundamental transverse magnetic mode (TM0) and the fundamental transverse electric mode (TE0), which are two modes that can exist in the waveguide in the pump wave, may become the same. This may cause the pump wave, which is the fundamental transverse magnetic mode (TM0), to move to the fundamental transverse electric mode (TE0). Curve section 1 (130) and curve section 2 (130_2) are each curves that rotate by 90 degrees, and may be curves that rotate by 180 degrees in total. The regions where the modes move may also exist in curve section 1 (130) and curve section 2 (130_2), respectively.

[0068] In order for the input light (pump wave) that has moved from the fundamental transverse magnetic mode (TM0) to the fundamental transverse electric mode (TE0) to return from the fundamental transverse electric mode (TE0) to the fundamental transverse magnetic mode (TM0), curve section 1 (130) and curve section 2 (130_2) may include a straight path of a preset length.

[0069]

[0070] FIG. 4 is a diagram showing a temporal distance compensation device in a quantum optical circuit according to an embodiment of the present disclosure.

[0071] The first temporal distance compensation device (100) of FIG. 4 may be an exemplary form of the first temporal distance compensation device (100) described in FIG. 3. Descriptions of each component of FIG. 4 are the same as those described in FIG. 3 and are therefore omitted. The first temporal distance compensation device (100) and the second temporal distance compensation device (100_2) may be connected as illustrated in FIG. 4 through curve section 1 (130) and curve section 2 (130_2).

[0072]

[0073] FIG. 5 is a diagram illustrating a temporal distance compensation device in a quantum optical circuit according to an embodiment of the present disclosure.

[0074] Referring to FIG. 5, the temporal distance compensation device (200) may include a nonlinear optical source (240), a polarization separation section (210), a taper section (220), and a curve section (230).

[0075] From the polarization separation section (210), the waveguide can be separated into a first waveguide and a second waveguide, and thereafter, the tapered section (220) and the curved section (230) can also be separated into a first waveguide and a second waveguide.

[0076] A nonlinear optical source (240) can provide input light used in a temporal distance compensation device (200) by converting it to have desired characteristics. For example, the nonlinear optical source (240) can be Periodically Poled Lithium Niobate (PPLN).

[0077] The nonlinear optical source (240) can provide a pump wave, a signal wave, and an idler wave, and can set the group velocity of each wave in a desired form by considering the characteristics of the waveguide, the wavelength of each wave, the effective index, etc. The nonlinear optical source (240) can provide a pump wave, a signal wave, and an idler wave by making the group velocity of the pump wave and the idler wave the same and setting the group velocity of the signal wave to be faster than the group velocity of the pump wave.

[0078] In integrated photonics, the vertical and horizontal lengths of the waveguide through which light (e.g., pump wave, signal wave, idler wave) propagates can be smaller than the wavelength of the light. In this case, the dispersion of the light is affected not only by the material dispersion but also by the geometric dispersion due to the waveguide structure. Leveraging this characteristic of integrated optics, dispersion engineering through the waveguide structure is possible. Furthermore, dispersion engineering can be used to design the group velocities of the optical modes (e.g., pump wave, signal wave, idler wave) participating in the nonlinear optical process. By matching the group velocities of the optical modes, the number of delay lines and directional couplers required for pseudo-group velocity matching can be reduced. For example, three optical modes, pump wave, signal wave, and idler wave, can be used in the polarization separation section (210). At this time, if the group velocities of the pump wave and the idler wave are matched through a distributed design, only the signal wave has a different group velocity, so similar group velocity matching can be implemented with only a delay line and directional coupler for the signal wave.

[0079] Therefore, only one delay line (e.g., the second waveguide) needs to be designed. For example, in the case of a waveguide structured by directly etching a thin-film lithium niobate (TFLN) film, the group velocities of the pump and idler waves can be matched under specific wavelength conditions.

[0080] This situation where the group velocities of two modes (e.g., the pump wave and the idler wave) match is called asymmetric group velocity matching (aGVM). Asymmetric group velocity matching can be used to improve the purity of heralded single-photon sources and enhance the mode selectivity of quantum frequency converters by implementing a single Schmidt mode. Therefore, not only can quasi-group velocity matching be efficiently implemented through a distributed design, but it can also enable the fabrication of nonlinear quantum devices operating in a single Schmidt mode.

[0081] For example, the key parameters can be a) waveguide width b) waveguide height c) etch depth d) sidewall angle e) material composition (e.g., doping concentration). The design process can include the following steps: a) Initial structure setup: Define the basic waveguide structure. b) Mode analysis: Calculate the dispersion characteristics of each mode using FDE or other mode analysis tools. c) Parameter optimization: Adjust the design parameters to match the group velocities of the desired modes. d) Iterative calculation: Repeat steps b) and c) until the optimal structure is found. e) Performance verification: Verify the performance of the final design using EME or FDTD simulation. In the present disclosure, asymmetric group velocity matching is implemented through a design method including waveguide width: 890 nm, film thickness: 500 nm, etch depth: 300 nm, sidewall angle: 68°, and platform: x-cut thin film lithium niobate (TFLN).

[0082] The nonlinear optical source (240) can be set so that the sum of the energy (or frequency) of the signal wave and the idler wave is equal to the energy (or frequency) of the pump wave. At the first point (ST1) where the input light is transmitted to the polarization separation section (210) in the nonlinear optical source (240) of the embodiment of FIG. 5, the pump wave may be in a transverse magnetic mode (TM0) at a wavelength of 775 nm, the signal wave may be in a transverse electric mode (TE0) at a wavelength of 1550 nm, and the idler wave may be in a transverse magnetic mode (TM0) at a wavelength of 1550 nm. Some characteristics, such as the modes of the pump wave, the signal wave, and the idler wave, may change during the process of propagating through the waveguide.

[0083] The dimensions included in the temporal distance compensation device (200) of FIG. 5 can be designed as follows. In the preparation area (211) of the polarization separation section (210), the width of the first waveguide (211_1) can be designed to linearly increase from 0.89 um to 1.24 um, the width of the second waveguide (211_2) can be designed to linearly increase from 2.41 um to 2.95 um, and the gap between the first waveguide and the second waveguide can be designed to decrease from 0.75 um to 0.3 um.

[0084] The coupling region (212) can be designed so that the total width (sum of the upper widths of the two waveguides) is maintained at 4.2 um, the lower gap between the first waveguide (212_1) and the second waveguide (212_2) is maintained at 0.3 um, the width of the first waveguide (212_1) is expanded to 1.32 um, and the width of the second waveguide (212_2) is reduced to 2.88 um.

[0085] The escape region (213) can be designed so that the lower gap between the first waveguide (213_1) and the second waveguide (213_2) is maintained at 0.3 um, the width of the first waveguide (213_1) is expanded to 1.55 um, and the width of the second waveguide (213_2) is reduced to 2.65 um.

[0086] The length of the preparation area (211) may be 1.5 mm, the length of the coupling area (212) may be 1.25 mm, and the length of the escape area (213) may be 1.5 mm.

[0087] In the polarization separation section (210), the signal wave of the first waveguide can be converted from the fundamental transverse electric mode (TE0) to the first transverse electric mode (TE) and moved to the second waveguide. The pump wave and the idler wave can remain in the first waveguide in the fundamental transverse magnetic mode (TM0).

[0088] When examining the cross sections (S_ST2, S_ST3) of the first waveguide and the second waveguide from the second point (ST2) entering the coupling region (212) to the third point where the coupling region (212) ends, it can be confirmed that the signal wave moves from the first waveguide to the second waveguide.

[0089] The taper section (220) may be an adiabatic taper. The taper section (220) may convert the mode of the signal wave. The signal wave, which is the first transverse electric mode (TE1), may be susceptible to curve loss. Therefore, the signal wave may be converted to the fundamental transverse magnetic mode (TM0) in the taper section (220) before entering the curve section (230), thereby reducing optical loss. Since the idler wave or pump wave may also increase curve loss in a waveguide with a wide linewidth, the taper section (220) may be designed in a form that reduces the linewidth of the waveguide. The taper section (220) may include a straight path for controlling the delay time.

[0090] The curve section (230) may be an Euler bend. In the curve section (230), the waveguide may be designed in a curved shape to rotate in order to change the direction of propagation of the input light.

[0091] Due to the anisotropy of lithium niobate (LN), the effective refractive index changes as the propagation direction of the waveguide changes, and the effective refractive indices of the fundamental transverse magnetic mode (TM0) and the fundamental transverse electric mode (TE0), which are two modes that can exist in the waveguide in the pump wave, may become the same. This may cause the pump wave, which is the fundamental transverse magnetic mode (TM0), to shift to the fundamental transverse electric mode (TE0).

[0092] The curve section (230) may include a straight path of a preset length so that the input light (pump wave) that has moved from the fundamental transverse magnetic mode (TM0) to the fundamental transverse electric mode (TE0) can return from the fundamental transverse electric mode (TE0) to the fundamental transverse magnetic mode (TM0). The curve section (230) illustrated in Fig. 5 corresponds to a 90-degree rotation, which is half of a 180-degree rotation curve.

[0093] a01 may be 1.5 mm, a02 may be 1.25 mm, a03 may be 1.5 mm, a04 may be 0.1 mm, and a06 may be 1 mm. a05 may be the length of the first straight path (222) included in the first waveguide, and may be configured to compensate for the temporal separation between the pump wave / idler wave and the signal wave. The length of the first straight path (222) is adjustable, and for example, the length a05 of the first straight path (222) may be set to 306.8 um (hereinafter, micrometers are expressed as um) to compensate for the temporal separation occurring in the nonlinear optical source (240) which is a 6 mm PPLN.

[0094] b01 can be 0.75um, b02 can be 0.89um, b03 can be 2.41um, b04 can be 0.3um, b05 can be 1.24um, b06 can be 2.96um, b07 can be 1.32um, b08 can be 2.88um, b09 can be 1.55um, b10 can be 2.65um, b11 can be 1.1um, b12 can be 1.1um, b13 can be 50um, and b14 can be 55.3um.

[0095] As described in curve section 1 (130) of FIG. 3, the pump wave (pump) that has moved from the basic transverse magnetic mode (TM0) to the basic transverse electric mode (TE0) can return from the basic transverse electric mode (TE0) to the basic transverse magnetic mode (TM0), so that the curve section 1 (130) and the curve section 2 (130_2) may have a length b15 corresponding to a straight path of a preset length. In the case of the temporal distance compensation device (200) of the present disclosure, the horizontal axis s1 position may correspond to the length of the straight path as illustrated in FIG. 7. The s1 position corresponds to 5.4 um, and b15 may be 2.7 um since it corresponds to half of the second straight path.

[0096] The performance of the temporal distance compensation device (200) can be more accurately predicted and the structure can be optimized through the EME (Eigenmode Expansion) method, the FDE (Finite Difference Eigenmode) method, or various simulation analysis techniques.

[0097]

[0098] FIG. 6 is a drawing for explaining a mode in a polarization separation section according to an embodiment of the present disclosure.

[0099] Referring to FIGS. 5 and 6, the polarization separation section may be an adiabatic polarizing beam splitter (APBS). FIG. 6 (a) is a diagram of the effective refractive index of supermodes in a second waveguide (auxiliary waveguide) of a polarization separation section having a wavelength of 1550 nm and a width of 4.2 μm, and FIG. 6 (b) is a diagram of the effective refractive index of supermodes in a first waveguide (primary waveguide) of a wavelength of 775 nm.

[0100] Fig. 6 (a) The signal wave, which is the fundamental transverse electric mode (TE0) at 1550 nm, can be converted into the first transverse electric mode (TE1) through the anti-crossing of mode 3 and mode 4. In Fig. 6 (a), there is a region where mode 4 and mode 2 come closer (P11) and move away (P12). This region is where mode coupling occurs. When the signal wave slowly passes through this region, the signal wave continues to maintain mode 4, and through this, the signal wave can move from the first waveguide to the second waveguide.

[0101]

[0102] FIG. 7 is a drawing for explaining the length of a straight path in a curved section according to an embodiment of the present disclosure.

[0103] Referring to FIGS. 5 and 7, the curved section may be an Euler band. The horizontal axis of the graph of FIG. 7 represents the length of the second straight path in the first waveguide curved section (231), which is a length corresponding to twice b15 in FIG. 5, and the vertical axis represents TM0 - TM0 transmission rate. FIG. 7 shows the transmission efficiency of the fundamental transverse magnetic mode (TM0) according to the length of a straight waveguide (or second straight path) inserted between two curved sections (each section corresponding to a 90-degree rotation of the Euler band). The transmission rate of the fundamental transverse magnetic mode (TM0) can be optimized by adjusting the length of the straight waveguide in the curved section. Since the maximum transmission rate occurs at a length of approximately 5.4 um, b15 in Fig. 5 can be set to 2.7 um, in which case stability can be secured by maintaining the fundamental transverse magnetic mode (TM0) while the pump wave passes through the curve section (231).

[0104]

[0105] FIG. 8 is a diagram illustrating the use of N connected temporal distance compensation devices in a quantum optical circuit according to an embodiment of the present disclosure. FIG. 9 is a diagram illustrating the result of correcting temporal distance using a temporal distance compensation device in a quantum optical circuit according to an embodiment of the present disclosure.

[0106] The temporal distance compensation devices described in FIG. 5 can be used by connecting N of them as illustrated in FIG. 8. For example, after the first nonlinear optical source (400_1), a polarization separation section, a taper section, and a curve section are formed, and a first device (300_1) in which the curve section, the taper section, and the polarization separation section are repeatedly formed in a symmetrical shape is connected, and then a second nonlinear optical source (400_2) can be connected. Depending on the number of temporal distance compensation devices (or nonlinear interaction regions), quantum compression can be increased.

[0107] Referring to Fig. 9, when temporal drift is fully compensated for (full compensation, FC), it can be seen that quantum compression increases linearly with the number of interaction regions (N). Compared to when temporal drift is not compensated for at all (no compensation, NC), a large quantum compression gain can be confirmed even considering realistic optical losses (NC). This allows for high nonlinear optical effects without increasing the optical power, and high compression states can be achieved while avoiding parasitic effects such as temporal alignment effects. High compression states are essential for implementing error-tolerant optical quantum computing, and the present disclosure can also play an important role in implementing non-Gaussian states, which are essential for implementing continuous-variable optical quantum computing technology through high nonlinearity.

[0108] In quantum frequency conversion, selectivity is also a key performance indicator, in addition to photon conversion efficiency. However, due to the temporal separation between optical modes (e.g., pump wave / signal wave / idler wave), it is difficult to simultaneously achieve high conversion efficiency and selectivity. This is because strengthening the interaction for high conversion efficiency increases the conversion efficiency of undesired optical modes due to the temporal alignment effect. However, using the temporal separation compensation proposed in this disclosure, high conversion efficiency can be achieved while avoiding the temporal alignment effect.

[0109]

[0110] The various embodiments of the present disclosure described above can be combined with additional embodiments and modified within the scope understood by those skilled in the art in light of the detailed description above. It should be understood that the embodiments of the present disclosure are illustrative in all respects and not restrictive. For example, each component described as a single component may be implemented in a distributed manner, and likewise, components described as distributed may be implemented in a combined manner. Accordingly, all changes or modifications derived from the meaning, scope, and equivalent concepts of the claims of the present disclosure should be construed as being included within the scope of the present disclosure.

Claims

1. In a device that compensates for the temporal distance of a nonlinear quantum optical element, It includes an optical waveguide that propagates input light along a specific path, The above optical waveguide is A nonlinear optical source section transmitting input light containing multiple modes; A polarization separation section that separates the above multiple modes; a taper section for converting the above separated mode; and Includes a curve section that changes the direction of propagation of input light; The above multiple modes include a pump wave, a signal wave, and an idler wave, The group velocities of the pump wave and the idler wave are identical, and the group velocity of the signal wave is different from that of the pump wave or the idler wave. Temporal distance compensation device.

2. In paragraph 1, The optical waveguide is separated into a first waveguide and a second waveguide in the polarization separation section, The above pump wave and idler wave are transmitted to the first waveguide, The signal wave is characterized in that it is transmitted by moving from the first waveguide to the second waveguide. Temporal distance compensation device.

3. In paragraph 2, The pump wave and idler wave are characterized in that they are fundamental transverse magnetic mode (TM0) among transverse magnetic (TM) modes, and the signal wave is characterized in that they are fundamental transverse electric mode (TE0) among transverse electric (TE) modes. Temporal distance compensation device.

4. In paragraph 3, The above signal wave and idler wave are the first wavelength, The pump wave is characterized in that the second wavelength is half of the first wavelength. Temporal distance compensation device.

5. In paragraph 4, In the above polarization separation section, the signal wave is characterized in that it is converted from the fundamental transverse electric mode (TE0) to the first transverse electric mode (TE1). Temporal distance compensation device.

6. In paragraph 2, The above polarization separation section includes a preparation region, a coupling region, and an escape region, The coupling region is characterized in that it moves the signal wave from the first waveguide to the second waveguide based on adiabatic coupling. Temporal distance compensation device.

7. In paragraph 5, The above taper section is characterized in that it converts the signal wave from the first transverse electric mode (TE1) to the fundamental transverse magnetic mode (TM0). Temporal distance compensation device.

8. In paragraph 7, The first waveguide is characterized in that it includes a first straight path set to a first length to control the delay time of the pump wave or idler wave in the taper section. Temporal distance compensation device.

9. In paragraph 8, The above curve section includes a first sub-section for rotating the path by a first angle, a second sub-section which is a straight path, and a third sub-section for rotating the path by a second angle. In the first sub-section of the first waveguide, the pump wave is converted from the fundamental transverse magnetic mode (TM0) to the fundamental transverse electric mode (TE0), The second sub-section of the first waveguide is characterized in that it is set to a second length so that the pump wave can return from the fundamental transverse electric mode (TE0) to the fundamental transverse magnetic mode (TM0). Temporal distance compensation device.

10. A method for compensating for temporal drift of a nonlinear quantum optical element performed by a temporal drift compensation device, A step of transmitting input light including a pump wave, a signal wave, and an idler wave; and The step of transmitting the pump wave and the idler wave to the first waveguide and separating the signal wave from the first waveguide to the second waveguide; The group velocities of the pump wave and the idler wave are identical, and the group velocity of the signal wave is different from that of the pump wave or the idler wave. How to compensate for temporal distance.

11. In paragraph 10, In the step of transmitting the above input light, the pump wave and idler wave are the fundamental transverse magnetic mode (TM0) among the transverse magnetic (TM) modes, The above signal wave is characterized in that it is a basic transverse electric mode (TE0) among transverse electric (TE) modes. How to compensate for temporal distance.

12. In paragraph 11, Characterized in that the sum of the frequency of the signal wave and the frequency of the idler wave is equal to the frequency of the pump wave. How to compensate for temporal distance.

13. In paragraph 12, The step of separating further comprises a step of converting the signal wave from the basic transverse electrical mode (TE0) to the first transverse electrical mode (TE1). How to compensate for temporal distance.

14. In paragraph 13, characterized in that it further includes a step of converting the signal wave from the first transverse electric mode (TE1) to the fundamental transverse magnetic mode (TM0) to reduce optical loss that occurs when the signal wave passes through a curved path. How to compensate for temporal distance.

15. In paragraph 14, A step of changing the direction of propagation of input light in the first waveguide; The above conversion step is, A step of rotating the path of the input light by a first angle; A step of propagating the input light along a second straight path included in the first waveguide; and A step of rotating the path of the input light by a second angle; In the above first angle rotating step, the pump wave is converted from the fundamental transverse magnetic mode (TM0) to the fundamental transverse electric mode (TE0), The second straight path is characterized in that the second length is set so that the pump wave returns from the fundamental transverse electric mode (TE0) to the fundamental transverse magnetic mode (TM0). How to compensate for temporal distance.

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