COHERENT HIGH SPEED OPTICAL VALVE

A control circuit for controlling a timing, a pulse length, a valve electric field having the certain magnitude, and a pulse envelope of the valve electric field, so as to coherently control a response of a region of an insulator to a probe electric field, the response controlled with a temporal resolution equal to the pulse length and matching the pulse envelope.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to optical valves and methods of making the same.

2. Description of the Related Art

(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers as superscripts, e.g.,x. A list of these different publications ordered according to these reference numbers can be found below in the section entitled “References.” Each of these publications is incorporated by reference herein.)

Strong periodic driving with light offers the potential to coherently manipulate the properties of quantum materials on ultrafast timescales. Recently, strategies have emerged to drastically alter electronic and magnetic properties by optically inducing non-trivial band topologies1-6, emergent spin interactions7-11and even superconductivity12. However, the prospects and methods of coherently engineering optical properties on demand are far less understood.13

In many applications, the optical response of a material (e.g. transmission, absorption, index of refraction) needs to be altered at high speeds. For example, in a photonic computing circuit, the faster an optical logic gate can switch, the higher the information processing speed. Since the optical properties of a material are set by its electronic band structure, it is important to develop ways to tune electronic band structures at high speeds. Electro-optic effects and opto-mechanical effects are two of the primary pathways to achieve this and are used in commercial devices such as Pockel’s cells and acousto-optical modulators. However, these approaches are limited to MHz to GHz speeds. An alternative approach is the optical valve, or optical transistor - a device whose optical properties can be tuned by a second light source. Currently, optical valves are realized using materials that exhibit large changes in optical properties upon being heated by light (e.g. found in thermochromic smart glass), or with ensembles of atoms or atom-like objects confined in a cavity architectures whose optical properties change under irradiation. However, these schemes are typically limited to GHz speeds and only work for specific wavelengths of light. What is needed are improved methods of coherently controlling light. The present disclosure satisfies this need.

SUMMARY OF THE INVENTION

The present disclosure reports on a fundamentally new system for realizing an optical valve, which can be made using any electrically insulating crystal. Working embodiments described herein demonstrate significant changes in the optical properties (including, but not limited to, bandgap and nonlinear response) achieved by optically pumping an insulator at an optical frequency that is smaller than the bandgap of the insulator, and smaller than any in-gap excitation.

In one example, we demonstrate coherent control and giant modulation of optical nonlinearity in a van der Waals layered magnetic insulator (manganese phosphorus trisulfide MnPS3). By driving far off-resonance from the lowest on-site manganese d-d transition, we observe a coherent on-off switching of its optical second harmonic generation efficiency on the timescale of 100 femtoseconds with no measurable dissipation. At driving electric fields of the order of 109volts per metre, the on-off ratio exceeds 10 , which is limited only by the sample damage threshold. Floquet theory calculations14based on a single-ion model of MnPS3are able to reproduce the measured driving field amplitude and polarization dependence of the effect. This demonstration illustrates our approach can be applied to a broad range of insulating materials and can lead to dynamically designed nonlinear optical elements.

Devices and methods according to embodiments described herein include, but are not limited to, the following.1. An optical valve, comprising:an insulator comprising:a first state and a second state separated in energy by a bandgap andcoupled by a first dipole allowed transition; anda nonlinear susceptibility associated with the first dipole allowed transition;a source of a first (e.g., valving) electric field coupled to a region of the insulator, the valve electric field comprising:a first frequency corresponding to a photon energy smaller than the bandgap and any in gap energy corresponding to a second dipole allowed transition within the bandgap; anda certain magnitude selected for driving a virtual transition between the first state and the second state under Floquet conditions that increase the bandgap by an amount proportional to a square of the magnitude; anda control circuit controlling a timing, a pulse length, the magnitude and a pulse envelope of the valve electric field so as to coherently control a response of the region of the insulator to a second (e.g. probe) electric field, the response controlled with a temporal resolution equal to the pulse length and matching the pulse envelope.2. The optical valve of example 1, wherein the valve electric field having the certain magnitude dresses the states with Floquet sidebands characterized by the first state and the second state gaining a mixing factor cosα wherein α is proportional to the magnitude.3. The optical valve of example 1, wherein the probe electric field has a second frequency tuned for absorption by the bandgap prior to application of the valve electric field and the control circuit controls a transparency of the region of insulator for the probe electric field by modulating the bandgap.4. The optical valve of example 1, wherein the control circuit controls a nonlinear response of the region of the insulator to the probe electric field, wherein the nonlinear response is mediated by the nonlinear susceptibility being switched on or off by the valve electric field.5. The optical valve of example 4, wherein the probe electric field has a second frequency and the control circuit controls a detuning of the second frequency to either side of the first dipole allowed transition so as to enhance or suppress the nonlinear response.6. An optical rectifier or high harmonic generator comprising the optical valve of example 1, wherein the control circuit controls optical rectification or generation of higher harmonics of the probe electric field via the valve electric field.7. A cavity comprising the insulator of example 1, “wherein the cavity reduces the magnitude of the valve electric field required to modify the transparency for the electromagnetic radiation comprising the second electric field.8. An optical transistor comprising the optical valve of example 1, wherein the valve electric field modulates an optical response of the region to the probe electric field.9. The optical valve of example 1, wherein the insulator comprises a two-dimensional van der Waals layered magnetic insulator or a 2D exfoliable material.10. The optical valve of example 9, wherein the first state is a spin state comprising A1gsymmetry and the second state has charge transfer character.11. The optical valve of example 1, wherein the insulator comprises ions disposed in two dimensional layers of a honeycomb lattice.12. The optical valve of example 11, wherein the ions each have spin magnetic moment moments adopting a Neel antiferromagnetic (AFM) arrangement that breaks the inversion symmetry of the honeycomb lattice, allowing a second-order optical nonlinearity of the first dipole allowed transition.13. The optical valve of example 1, wherein the insulator comprises a magnetic insulator comprising manganese phosphorus trisulfide.14. The optical valve of example 1, wherein the pulse length is 500 femtoseconds or less.15. A device, comprising:a control circuit for controlling a timing, a pulse length, a first (e.g., valve) electric field having the certain magnitude, and a pulse envelope of the valve electric field, so as to coherently control a response of a region of an insulator to a second (e.g,. probe) electric field, the response controlled with a temporal resolution equal to the pulse length and matching the pulse envelope.16. The device of example 15, wherein the control circuit controls the magnitude so as to dress a first state and a second state of the insulator with Floquet sidebands characterized by the first state and the second state gaining a mixing factor cosα wherein α is proportional to the magnitude.17. The device of example 15, wherein the control circuit controls a transparency of the region of insulator for the probe electric field by modulating a bandgap of the insulator.18. The device of example 15, wherein the control circuit controls a nonlinear response of the region of the insulator to the probe electric field by gating or switching the valve electric field on or off.19. The device of claim 15, wherein the control circuit controls a detuning of a second frequency of the probe electric field to either side of the first dipole allowed transition between the first state and the second state so as to enhance or suppress a nonlinear response of the insulator to the probe electric field.20. A method of making an optical valve, comprising:providing an insulator comprising:a first state and a second state separated in energy by a bandgap andcoupled by a first dipole allowed transition; anda nonlinear susceptibility associated with the first the dipole allowed transition;coupling a first source of a valve electric field to a region of the insulator, the valve electric field comprising:a first frequency corresponding to a photon energy smaller than the bandgap and any in gap energy corresponding to a second dipole allowed transition within the bandgap; anda magnitude selected for driving a virtual transition between the first state and the second state under Floquet conditions that increase the bandgap by an amount proportional to a square of the magnitude; andcoupling a control circuit to the first source and a second source of a probe electric field, the control circuit controlling a timing, a pulse length, the valve electric field having the certain magnitude, and a pulse envelope of the valve electric field so as to coherently control a response of the region of the insulator to the probe electric field, the response controlled with a temporal resolution equal to the pulse length and matching the pulse envelope.21. The method of example 20 used for making the device of any of the examples 1-1922. A method of operating an optical valve, comprising:interacting a valve electric field with a probe electric field in a region of an insulator comprising:a first state and a second state separated in energy by a bandgap and coupled by a first dipole allowed transition; anda nonlinear susceptibility associated with the first the dipole allowed transition;wherein the valve electric field comprises:a first frequency corresponding to a photon energy smaller than the bandgap and any in gap energy corresponding to a second dipole allowed transition within the bandgap; anda magnitude selected for driving a virtual transition between the first state and the second state under Floquet conditions that increase the bandgap by an amount proportional to a square of the magnitude; andcontrolling a timing, a pulse length, the valve electric field having the certain magnitude, and a pulse envelope of the valve electric field so as to coherently control a response of the region of the insulator to the probe electric field, the response controlled with a temporal resolution equal to the pulse length and matching the pulse envelope.23. The method of example 22 used for operating the device of any of the examples 1-19.

DETAILED DESCRIPTION OF THE INVENTION

Technical Description

The present disclosure demonstrates the use of Floquet engineering as a non-thermal and broadly applicable strategy to modulate nonlinearity on ultrashort timescales, limited only by the drive pulse duration. Appreciable tuning requires strong driving (pump) electric fields Epucharacterized by a Floquet parameter

of order unity, where e is the electron charge, α is the atomic spacing, ℏ is the reduced Planck’s constant and Ω is the driving frequency. For a typical solid with α ≈ 3 Å, the requisite field is of the order of 109V m-1at optical or near-infrared frequencies, making runaway heating a major obstacle to experimentally realizing Floquet engineering. To mitigate this effect, embodiments described herein drive electrical insulators below their bandgap.

In typical examples, Floquet engineering can be used to modify the bandgap of a material. When the bandgap of a material changes, the wavelength range over which the material is transparent and absorbing changes. In one embodiment, a material that is naturally opaque to 400 nm light becomes transparent to that wavelength upon pumping at a wavelength above 600 nm. However, a variety of properties can be modulated using Floquet engineering, as illustrated in the following examples.

The layered honeycomb lattice magnetic insulator manganese phosphorus trisulfide (MnPS3) is an ideal demonstration platform for the following reasons. First, it exhibits a large direct bandgap Eg= 3.1 eV in the visible region24. Second, the Mn2+moments adopt a Neel antiferromagnetic (AFM) arrangement that breaks the inversion symmetry of its underlying lattice, allowing a finite second-order optical nonlinearity in the electric dipole (ED) channel. This has recently been detected by optical second harmonic generation (SHG) measurements with an SHG photon energy resonant with Egref.25). Third, the relatively low AFM ordering temperature (TN= 78 K) allows thermal- versus non-thermal-induced effects to be readily distinguished. Fourth, the timescale for spin dynamics, which may be induced by light directly via magneto-optical effects or indirectly via magneto-elastic coupling26, is limited to around 5 ps based on the magnetic exchange interaction strength27. Therefore, any dynamics occurring on the timescale of a femtosecond driving pulse can be confined to the charge sector. Lastly, as the Mn 3d electrons are highly localized, the optical response and transport properties of MnPS3are well captured within a single ion picture28, which enables an analytical derivation of Floquet engineering effects from a microscopic model.

A single-ion model was developed to understand the AFM-order-induced static SHG from MnPS3. Owing to the absence of inversion symmetry, this response is dominated by a bulk ED process of the form

where the second-order susceptibility tensor

governs the relationship between the incident (probe) electric field

(w) at frequency ω and the polarization induced at twice the incident probing frequency Pi(2w), and the indices i, j, k run over the x, y and z coordinates. As shown in the experiments, we exclusively detect the time-reversal odd (c type)29component of

which couples linearly to the AFM order parameter. For a near resonant process where 2ℏω ≈ Eg, the quantum mechanical expression for

is given by30

where the sum is performed over Mn2+ions in a unit cell, |i〉, |m〉 and |f〉 are the ground, intermediate and final states of the SHG process, Ei, Emand Efdenote their respective energies, r is the position operator, and γfis a phenomenological decay rate of the final state (‘Determination of Egand γf’ in Methods). In the presence of an octahedral crystal field imposed by the sulfur ions, the five-fold degenerate Mn 3d orbitals split into a low-energy t2gtriplet and a high-energy egdoublet. The ground state is a high-spin (S = 5/2) state characterized by a

orbital configuration with6A1gsymmetry. According to previous optical absorption measurements (FIG.1A)28, the intermediate state has predominantly

character (S = 3/2) and the final state has predominantly S 3p → Mn 3d charge transfer (CT) character (S = 5/2). The |f〉 state has opposite parity to the |i〉 and |m〉 states.

By introducing spin-orbit coupling λ and a trigonal distortion of the crystal field η as perturbations to the states described above31, optical transitions |i〉 → |m〉 and |m〉 → |f〉 become ED allowed (FIG.1B). Upon coherently summing the single-ion contributions from two Mn2+sites in the unit cell, one obtains

, where (Sz,1- Sz,2) is the staggered moment perpendicular to the honeycomb plane. The coefficient βijkencodes the symmetry of the underlying crystal through the matrix elements in equation (1). To capture the loss of three-fold rotational symmetry owing to coupling between adjacent honeycomb layers displaced along x, we assign unequal weight to the dipole matrix elements along x and y.

To verify this static SHG model, rotational anisotropy (RA) measurements32were performed using near-resonant probe light (ℏω = 1.55 eV). The beam was focused obliquely onto a bulk MnPS3single crystal and specular reflected SHG light was collected as a function of the scattering plane angle φ (FIG.1C). Above TN, we observe a weak temperature-independent SHG signal arising from time-reversal even (i type) higher multipole bulk crystallographic SHG processes (FIG.1D), consistent with the report in25. Below TN, the intensity, collected at φ = 60°, undergoes a steep upturn that can be fitted to a power law

with β = 0.32. This is in excellent agreement with the critical exponent of the AFM order parameter (β = 0.32) obtained from neutron diffraction33(‘Linear coupling of

to the AFM order parameter’ in Methods), confirming its linear coupling to

as predicted in our model. The enhanced anisotropy of the RA pattern below TNarises from interlayer coupling and is fully captured in our model through the βijkcoefficient (FIG.1D, inset).

The effect of electric field oscillating at a subgap frequency on the electronic spectrum of MnPS3can be studied within our single-ion model. As this drive mainly hybridizes |i〉 and |f〉 owing to their opposite parity and equal spin, the three-level problem can be simplified to a two-level one, described by the following time-dependent Hamiltonian

where H0is the unperturbed 2 × 2 Hamiltonian, r is the position operator and t is time. By diagonalizing the time-independent Floquet Hamiltonian3(HF)mn=

truncated at the ±3 rd Floquet sector (FIG.2A, inset), where m and n denote the index of the Hilbert space basis and δ is the Kronecker delta, we obtain the pump field dressed initial and final states |i′〉 and |f′〉

where ΔE is the energy shift and the hybridization is parameterized by a mixing amplitude sin α and phase ϕ(t), which all depend on Epu(Supplementary Section 2 in ref. 38). In this model, periodic driving serves to modify the single-ion states involved in an SHG scattering process. This is distinct from Floquet engineering proposals where periodic driving is used to renormalize the low-energy Hamiltonian of a many-body system7. For a Gaussian pulsed drive, the calculations show that in the adiabatic limit where the pulse width far exceeds Ω-1, both the bandgap and hybridization undergo a temporal increase that follows the pulse envelope (FIG.2A), attaining maximum values at the peak pump field

The maximal mixing amplitude scales linearly with

as expected from a perturbative treatment, whereas the maximal bandgap increase (2ΔE) scales like the square of

Although this quadratic dependence is reminiscent of the optical Stark effect34,35, the Floquet treatment goes beyond the rotating wave approximation by including both optical Stark and Bloch-Siegert shifts36(FIG.2B) as well as the influence of higher Floquet sectors, predicting 2ΔEmaxas large as 188 meV for

Both mixing and bandgap widening, imparted by a coherent modulation of the two-level Hamiltonian composed of |i〉 and |f〉, should suppress the magnitude of

because the former reduces the amplitude of states in the zeroth Floquet sector-the dominant contribution to

-by a factor of cos α, whereas the latter shifts the resonance condition away from ℏω = 1.55 eV. The fast-oscillating pump field induces a quasi-static change in the time-averaged value of

that follows the slower pump-pulse envelope, consistent with a Floquet description. To quantify these effects, we computed the expected change in χ

and the resulting modulation of the magnetic contribution to the SHG intensity ƒmag(FIG.1D) within our single-ion model using the dressed initial and final states, assuming ℏΩ well below the6A1g→4T1gtransition and Epuparallel to the nearest-neighbour Mn - Mn bond (pump field polarization angle θ = 90° ). As shown in the inset ofFIG.2B, the model predicts an inverse power-law-like dependence of |∧mag on the driving field amplitude, indicating that the suppression is predominantly caused by energy shifts that affect the denominator in equation (1). Remarkably , the model predicts that Floquet engineering can impart a giant suppression exceeding 90% at readily attainable field strengths of the order of 109V m-1.

To experimentally test our prediction, time-resolved pump-probe RA SHG measurements were performed in the AFM phase of MnPS3. To minimize dissipation and decoherence, the pump photon energy was tuned below the6A1g→4T1gtransition edge near 2 eV to avoid absorption, but above 0.5 eV to suppress the effects of quantum tunnelling between the valence and conduction bands, phonon resonances and photo-assisted inter-site hopping (Supplementary Section 3 in ref. 38) that are more pronounced at lower frequencies. Gaussian pump- and probe-pulse envelopes of 120 fs and 80 fs duration were used, respectively, satisfying the adiabatic condition.FIG.3Ashows instantaneous RA patterns at selected time delays measured using θ = 90° and

. The magnitude of the RA patterns is drastically reduced during pumping and can be fit by simply decreasing all

elements uniformly. The temporal evolution of the RA patterns is completely symmetric about time t = 0-the instant when pump and probe pulses are exactly overlapped-and the transient SHG intensity change

ΔImag/Imagexhibits a temporal profile that matches the theoretically predicted SHG profile convolved with the probe pulse (FIG.3B). These data indicate a coherent and uniform modulation of the 2′/m magnetic point group allowed

elements with no measurable dissipation (‘Time-resolved SHG data at 70 K and 90 K’ in Methods), in accordance with a Floquet engineering process. The maximal suppression of Imagreaches around 90% and is unchanged upon sweeping ℏΩ from 0.66 eV to 1.55 eV, in full agreement with our theoretical model (Supplementary Section 2 in ref. 38).

In contrast, measurements performed with ℏΩ tuned near

the6A1g→4T1gabsorption peak reveal dynamics that are strongly asymmetric about t = 0. Following an initial fast coherent reduction of Imag, there is a slow exponential decay to 100% suppression, where it remains for more than 500 ps (FIG.3D). The decay and plateau are consistent with an incoherent quasi-thermal melting of the AFM order via heat transfer from the optically excited electronic subsystem to the spin subsystem, followed by a very slow cooling of the pumped region through diffusion (‘Proof of the heating picture for ℏΩ = 2.07 eV drive’ in Methods in ref. 38). This interpretation is further corroborated by instantaneous RA data acquired within the exponential decay time window, which directly map onto our temperature-dependent RA data (FIG.3C).

To directly confirm the predicted bandgap widening effect (FIGS.2A2B), transient SHG spectroscopy measurements were performed with ℏΩ = 0.66 eV. The equilibrium SHG spectrum exhibits a steep intensity upturn near the band edge of MnPS3(FIG.3E), closely following the linear optical absorption spectrum24. This is expected as the absorption spectrum is featureless over the measured range of incident (fundamental) photon energies. Upon driving, the band edge feature instantaneously shifts to higher energy, which is opposite to the typical response of electronic gaps to photoexcitation. The size of the positive shift at t = 0 increases monotonically with

and agrees reasonably well with our theoretically predicted values (FIGS.3F,3G), further supporting the Floquet engineering interpretation.

As both the bandgap widening and level mixing are dependent on the Rabi frequency 〈f|er • Epu/ℏ|i〉, we expect the magnitude of SHG modulation to be tunable by both the electric field amplitude and polarization of the pump pulse. To study this relationship, a comprehensive experimental mapping of ΔI/Imag(t = 0) was performed as a function of both

and θ using ℏΩ = 0.66 eV (FIG.4A). A comparison with our model calculation performed over the same parameter space (FIG.4B), using the same weighting of dipole matrix elements along x and y as in our static model to account for inter-layer coupling, shows excellent agreement in overall trend. More detailed comparisons can be drawn by taking different one-dimensional cuts through our dataset. For a fixed θ, ΔImag/Imagexhibits an expected inverse power-law-like dependence on the pump field in both experiment and theory (FIG.4C), with good agreement on the level of suppression. For a fixed pump field, we observe a sinusoidal dependence of ΔImag/Imagon θ that is reproduced in our calculations (FIG.4D). Although the three-fold rotational symmetry of an isolated honeycomb layer forbids an anisotropic Rabi frequency, this is broken in bulk MnPS3owing to the layer stacking (FIG.1D, inset), resulting in a maximum (minimum) Rabi frequency at θ = 90°(0°). The fact that the θ dependence remains largely unchanged upon rotating φ (FIG.4E) confirms that the anisotropy is intrinsic to the crystal and is unrelated to the relative polarization of the pump and probe light. The close agreement between our measurements and theoretical calculations, which contain no free parameters, confirms the validity of our single-ion treatment and highlights its dominant role over photo-assisted inter-site hopping effects in our experiments (Supplementary Section 3 in ref. 38).

Possible Modifications and Variations

The Floquet engineering strategy demonstrated here can be broadly applied to coherently control a variety of nonlinear optical processes including optical rectification and higher harmonic generation. Moreover, both coherent enhancement and suppression of the nonlinear response can in principle be realized by tuning the probe photon energy to either side of an absorption resonance peak. Introducing few-layer exfoliable materials such as MnPS3into cavity architectures37enables coherently switchable optical, optoelectronic and magnetic devices with reduced external field thresholds.

Hardware Environment

FIG.5is an exemplary hardware and software environment 1500 (referred to as a computer-implemented system and/or computer-implemented method) used to implement one or more embodiments of the invention. The hardware and software environment includes a computer502and may include peripherals. Computer502may be a user/client computer, server computer, or may be a database computer. The computer502comprises a hardware processor504A and/or a special purpose hardware processor504B (hereinafter alternatively collectively referred to as processor504) and a memory506, such as random access memory (RAM). The computer502may be coupled to, and/or integrated with, other devices, including input/output (I/O) devices such as a keyboard514, a cursor control device516(e.g., a mouse) a pointing device, pen and tablet, touch screen, multi-touch device, etc.) and a printer528. In one or more embodiments, computer502may be coupled to, or may comprise, a portable or media viewing/listening device532. In yet another embodiment, the computer502may comprise a multi-touch device, mobile phone, or other internet enabled device executing on various platforms and operating systems.

In one embodiment, the computer502operates by the hardware processor504A performing instructions defined by the computer program510under control of an operating system508. The computer program510and/or the operating system508may be stored in the memory506and may interface with the user and/or other devices to accept input and commands and, based on such input and commands and the instructions defined by the computer program510and operating system508, to provide output and results.

Output/results may be presented on the display522or provided to another device for presentation or further processing or action. The image may be provided through a graphical user interface (GUI) module518. Although the GUI module518is depicted as a separate module, the instructions performing the GUI functions can be resident or distributed in the operating system508, the computer program510, or implemented with special purpose memory and processors.

Some or all of the operations performed by the computer502according to the computer program510instructions may be implemented in a special purpose processor504B. In this embodiment, some or all of the computer program510instructions may be implemented via firmware instructions stored in a read only memory (ROM), a programmable read only memory (PROM) or flash memory within the special purpose processor504B or in memory506. The special purpose processor504B may also be hardwired through circuit design to perform some or all of the operations to implement the present invention. Further, the special purpose processor504B may be a hybrid processor, which includes dedicated circuitry for performing a subset of functions, and other circuits for performing more general functions such as responding to computer program510instructions. In one embodiment, the special purpose processor504B is an application specific integrated circuit (ASIC) or field programmable gate array (FPGA). In other examples, special purpose processor may comprise a graphics processing unit (GPU).

The computer502may also implement a compiler512that allows an application or computer program510written in a programming language such as C, C++, Assembly, SQL, PYTHON, PROLOG, MATLAB, RUBY, RAILS, HASKELL, or other language to be translated into processor504readable code. Alternatively, the compiler512may be an interpreter that executes instructions/source code directly, translates source code into an intermediate representation that is executed, or that executes stored precompiled code. Such source code may be written in a variety of programming languages such as JAVA, JAVASCRIPT, PERL, BASIC, etc. After completion, the application or computer program510accesses and manipulates data accepted from I/O devices and stored in the memory506of the computer502using the relationships and logic that were generated using the compiler512.

In one embodiment, instructions implementing the operating system508, the computer program510, and the compiler512are tangibly embodied in a non-transitory computer-readable medium, e.g., data storage device520, which could include one or more fixed or removable data storage devices, such as a zip drive, floppy disc drive524, hard drive, CD-ROM drive, tape drive, etc. Further, the operating system508and the computer program510are comprised of computer program510instructions which, when accessed, read and executed by the computer502, cause the computer502to perform the steps necessary to implement and/or use the present invention or to load the program of instructions into a memory506, thus creating a special purpose data structure causing the computer502to operate as a specially programmed computer executing the functions of the control circuit controlling the valve electric field and probe electric field according to the functionalities described herein. Computer program510and/or operating instructions may also be tangibly embodied in memory506and/or embodied in or coupled to source530of the pulses206comprising electromagnetic fields (e.g.,530may comprise sources804,808), thereby making a computer program product or article of manufacture according to the invention. As such, the terms “article of manufacture,” “program storage device,” and “computer program product,” as used herein, are intended to encompass a computer program accessible from any computer readable device or media. Computer500may comprise or be coupled to530.

FIG.6schematically illustrates a typical distributed/cloud-based computer system600using a network604to connect client computers602to server computers606. A typical combination of resources may include a network604comprising the Internet, LANs (local area networks), WANs (wide area networks), SNA (systems network architecture) networks, or the like, clients602that are personal computers or workstations (as set forth inFIG.5), and servers606that are personal computers, workstations, minicomputers, or mainframes (as set forth inFIG.5). However, it may be noted that different networks such as a cellular network (e.g., GSM [global system for mobile communications] or otherwise), a satellite based network, or any other type of network may be used to connect clients602and servers606in accordance with embodiments of the invention.

A network604such as the Internet connects clients602to server computers606. Network604may utilize ethernet, coaxial cable, wireless communications, radio frequency (RF), etc. to connect and provide the communication between clients602and servers606. Further, in a cloud-based computing system, resources (e.g., storage, processors, applications, memory, infrastructure, etc.) in clients602and server computers606may be shared by clients602, server computers606, and users across one or more networks. Resources may be shared by multiple users and can be dynamically reallocated per demand. In this regard, cloud computing may be referred to as a model for enabling access to a shared pool of configurable computing resources.

Clients602may execute a client application or web browser and communicate with server computers606executing web servers610. Such a web browser is typically a program such as MICROSOFT INTERNET EXPLORER/EDGE, MOZILLA FIREFOX, OPERA, APPLE SAFARI, GOOGLE CHROME, etc. Further, the software executing on clients602may be downloaded from server computer606to client computers602and installed as a plug-in or ACTIVEX control of a web browser. Accordingly, clients602may utilize ACTIVEX components/component object model (COM) or distributed COM (DCOM) components to provide a user interface on a display of client602. The web server610is typically a program such as MICROSOFT’S INTERNET INFORMATION SERVER.

Web server610may host an Active Server Page (ASP) or Internet Server Application Programming Interface (ISAPI) application612, which may be executing scripts.

Although the terms “user computer”, “client computer”, and/or “server computer” are referred to herein, it is understood that such computers602and606may be interchangeable and may further include thin client devices with limited or full processing capabilities, portable devices such as cell phones, notebook computers, pocket computers, multi-touch devices, and/or any other devices with suitable processing, communication, and input/output capability.

Of course, those skilled in the art will recognize that any combination of the above components, or any number of different components, peripherals, and other devices, may be used with computers602and606. Embodiments of the invention are implemented as a software protocol application on a client602or server computer606. Further, as described above, the client602or server computer606may comprise a thin client device or a portable device that has a multi-touch-based display.

Process Steps

FIG.7is a flowchart illustrating a method of making an optical valve or a system implementing the optical valve (referring also toFIGS.1A-1D2A2B3A–3G4A–4E5–6and8).

Block700represents obtaining an insulator100,802comprising a first state and a second state separated in energy by a bandgap and coupled by a first dipole allowed transition; and a nonlinear susceptibility associated with the first the dipole allowed transition. The step can comprise defining a input to the insulator (for receiving the probe and pump electromagnetic fields), a gating or channel region for interacting the pump and probe fields, and an output for outputting the probe electromagnetic field. The insulator may be patterned with waveguides and couplers, e.g., a photonic integrated circuit, for inputting and interacting the valve and probe electric fields.

Block702represents providing and coupling a source (e.g., a laser804) of electromagnetic radiation104having a pump (valving/valve/driving) electromagnetic/electric field806and a source808of electromagnetic radiation106comprising the second (e.g., probe) electromagnetic field. In one or more examples, the source808comprises a laser or a nonlinear medium, e.g., optical parametric amplifier, pumped by valving source804.

Without being bound by any specific scientific theory,FIG.3Bshows the frequency of the drive electric field does not play a big role in the gating, as long as it is sufficiently detuned from any in-gap transitions. If it is not detuned sufficiently, heating dominates the process (as illustrated inFIG.3D) and the gating effect will not be seen.

Block704represents coupling one or more control circuits500,810to the sources804,808for controlling the output of the sources (e.g., at least one of a timing, amplitude, pulse length204or frequency of the pump and/or probe electromagnetic fields or pulses206comprising the fields). ). In one or more examples, the sources of the pulses of the fields (e.g., the laser(s)) comprise the one or more control circuits e.g., as an embedded system or processor, e.g., so as to form smart or programmable sources. The one or more circuits may be in central controller or distributed among the sources. In one or more examples, the control circuit comprises an arbitrary waveform generator (AWG) outputting the timing control signals to the laser sources. In one or more examples, the AWG comprises an FPGA connected to a digital to analog converter.

In one or more examples, the one or more control circuits comprise a computer comprising or coupled to one or more processors; one or more memories; and one or more programs stored in the one or more memories, wherein the one or more programs executed by the one or more processors control the implementation of the coherent control described herein using the valving electric field.

Block706represents the end result, a device800or system comprising or implementing an optical valve or optical transistor, as illustrated inFIG.8.

Block708represents coupling the device (e.g., optical valve/transistor) in or to an application or system814comprising, for example, a circuit (e.g., photonic integrated circuit), a modulator, a cavity, a computer, a detector, or a rectifier. The probe electric field may be transmitted through system and carry signals or other information used by the system. The device may modulate the signals according to the configuration or requirements of the system.

Devices or systems according to embodiments described herein include, but are not limited to, the following.1.FIGS.1A-1D,FIG.2A, andFIG.8illustrate an example of an optical valve800, comprising:an insulator802,100comprising:a first state |i> and a second state |f>separated in energy by a bandgap Eg of the insulator802and coupled by a first dipole allowed transition102; anda nonlinear susceptibilityχijkEDassociated with the first dipole allowed transition102;a source (e.g., laser804) of a valve (or valving, or gating or first) electric field806,106coupled to a region820(e.g., gating or channel region) of the insulator, the valve electric field comprising:a first frequency corresponding to a photon energy smaller than the bandgap Eg and any in gap energy corresponding to a second dipole allowed transition within the bandgap; anda (e.g., a certain, predetermined, or particular) magnitude selected for driving a virtual transition200between the first state and the second state under Floquet conditions that increase the bandgap Eg by an amount proportional to a square of the magnitude; anda computer500or control circuit500,810controlling a timing, a pulse length204, the magnitude205and a pulse envelope208of the valve electric field806so as to coherently control a response of the region820of the insulator802to a probe or second electric field812,104the response controlled with a temporal resolution equal to the pulse length204and matching the pulse envelope208.2. The optical valve of example 1, wherein the valve electric field806having the certain magnitude205dresses the states with Floquet sidebands202characterized by the first state |i> and the second state |f> gaining a mixing factor cosα wherein α is proportional to the magnitude.3. The optical valve of example 1 or 2, wherein the probe electric field812has a second frequency tuned for absorption by the bandgap Eg prior to application of the valving electric field806and the control circuit500controls a transparency of the region820of insulator802for the probe electric field812by modulating the bandgap.4. The optical valve of any of the examples 1-3, wherein the control circuit500controls a nonlinear response of the region820of the insulator802to the probe electric field812, wherein the nonlinear response is mediated by the nonlinear susceptibility being switched on or off by the valve electric field806.5. The optical valve of example 4, wherein the probe electric field812has a second frequency and the control circuit500controls a detuning of the second frequency to either side of the first dipole allowed transition102so as to enhance or suppress the nonlinear response.6. An optical rectifier814or high harmonic generator comprising the optical valve800of any of the examples 1-5, wherein the control circuit500controls optical rectification or generation of higher harmonics of the probe electric field812via the valving electric field806.7. A cavity comprising the insulator of any of the examples 1-5, wherein the cavity reduces the magnitude of the valve electric field806required to modify the transparency for the electromagnetic radiation comprising the second/probe electric field812.8. An optical transistor comprising the optical valve of any of the examples 1-5, wherein the valve electric field806modulates an (e.g., optical) response of the region820to the probe electric field812.9.FIGS.1A-1Dillustrates an example of the optical valve of any of the examples 1-8, wherein the insulator100comprises a two- dimensional van der Waals layered magnetic insulator or a 2D exfoliable material.10.FIGS.1A-1Dillustrates an example of the optical valve of example 9, wherein the first state |i> is a spin state comprising A1gsymmetry and the second state |f> has charge transfer character.11.FIGS.1A-1Dillustrates an example of the optical valve of any of the examples 1-10, wherein the insulator100comprises ions108disposed in two dimensional layers of a honeycomb lattice110.12.FIGS.1A-1Dillustrates an example of the optical valve of example 11, wherein the ions108each have spin magnetic moment moments adopting a Neel antiferromagnetic (AFM) arrangement that breaks the inversion symmetry of the honeycomb lattice, allowing a second-order optical nonlinearity of the first dipole allowed transition.13.FIGS.1-14illustrate an example of the optical valve of example 1, wherein the insulator802comprises a magnetic insulator comprising manganese phosphorus trisulfide.14. The optical valve of any of the examples 1-13, wherein the pulse length204(FWHM) is500femtoseconds or less.15. A device800, comprising:a control circuit810or computer500for controlling a timing, a pulse length204, a valve electric field806having the magnitude205, and a pulse envelope208of the valve electric field, so as to coherently control a response of a region820of an insulator802to a probe electric field812, the response controlled with a temporal resolution equal to the pulse length204and matching the pulse envelope208.16. The device of example 15, wherein the control circuit810or computer500controls the magnitude205so as to dress a first state |i> and a second state |f> of the insulator with Floquet sidebands202characterized by the first state and the second state gaining a mixing factor cosα wherein α is proportional to the magnitude.17. The device of example 15 or 16, wherein the control circuit500or computer controls a transparency of the region820of insulator for the probe electric field812,106by modulating a bandgap Eg of the insulator.18. The device of any of the examples 15-17 , wherein the control circuit500or computer controls a nonlinear response of the region of the insulator802to the probe electric field812by gating or switching the valve electric field104,806on or off.19. The device of example 15, wherein the control circuit500or computer controls a detuning of a second frequency of the probe electric field812to either side of the first dipole allowed transition102between the first state |i> and the second state |f> so as to enhance or suppress a nonlinear response of the insulator802to the probe electric field.20. The device of any of the examples, wherein the insulator is patterned with an input, and output, waveguides, and couplers for inputting, outputting and interacting the valving and probe electric fields.21.FIG.9illustrates s method of operating an optical valve, comprising:interacting (Block900) a valving electric field with a probe electric field in a region of an insulator (or gating a response of the insulator to a probe electric field using a valve electric field) comprising:a first state and a second state separated in energy by a bandgap and coupled by a first dipole allowed transition; anda nonlinear susceptibility associated with the first the dipole allowed transition;wherein the valve electric field comprises:a first frequency corresponding to a photon energy smaller than the bandgap and any in gap energy corresponding to a second dipole allowed transition within the bandgap; anda magnitude selected for driving a virtual transition between the first state and the second state under Floquet conditions that increase the bandgap by an amount proportional to a square of the magnitude; andcontrolling (Block902) a timing, a pulse length, the valve electric field having the certain magnitude, and a pulse envelope of the valve electric field so as to coherently control a response of the region of the insulator to the probe electric field, the response controlled with a temporal resolution equal to the pulse length and matching the pulse envelope.22. The device or method of any of the examples 1-120, wherein the insulator comprises a charge transfer insulator.23. The device or method of any of the examples 1-21, wherein the insulator has the bandgap of around 1 eV or larger.24. The device or method of any of the examples, wherein the dipole allowed transitions are defined as transitions between states with opposite parities but the same spin quantum number.25. The device or method of any of the examples 1-23, wherein the valving electric field has the first frequency sufficiently detuned from any in-gap transitions so as to avoid the valving electric field from heating the insulator (see e.g.,FIG.3B), or to prevent any heating caused by the valving electric field from dominating (as illustrated inFIG.3D) the coherent control modulated by the magnitude of the valving electric field according to the valving/gating effects described herein.26. The device or method of any of the examples, wherein the control circuit comprises or is coupled to a computer comprising or coupled to one or more processors; one or more memories; and one or more programs stored in the one or more memories, wherein the one or more programs executed by the one or more processors control controlling a timing, a pulse length, the valve electric field having the certain magnitude, and a pulse envelope of the valve electric field.27. A computer500and/or control circuit810for controlling a timing of a valve electric field, a pulse length204of the first (e.g., valve) electric field806, a magnitude205or amplitude of the first (e.g., valve) electric field, and a pulse envelope206of the valve electric field incident with a probe electric field on a region820of an insulator802, so as to coherently control a response of the region of the insulator to the probe electric field812such that the response is controlled with a temporal resolution equal to the pulse length and matching the pulse envelope.28. A method of operating an optical valve, comprising:at least providing, selecting, or controlling a timing of a valve electric field806, a pulse length204of the valve electric field, a magnitude or amplitude205of the valve electric field, and a pulse envelope206of the valve electric field incident with a probe electric field on an insulator, so as to coherently control a response of the insulator to the probe electric field812such that the response is controlled with a temporal resolution equal to the pulse length and matching the pulse envelope, wherein:the insulator comprises:a first state and a second state separated in energy by a bandgap and coupled by a first dipole allowed transition; anda nonlinear susceptibility associated with the first the dipole allowed transition; andthe valve electric field comprises:a first frequency corresponding to a photon energy smaller than the bandgap and any in gap energy corresponding to a second dipole allowed transition within the bandgap; andthe magnitude is selected for driving a virtual transition between the first state and the second state under Floquet conditions that increase the bandgap by an amount proportional to a square of the magnitude.29. An optical valve, comprising:an insulator comprising:a first state and a second state separated in energy by a bandgap and coupled by a first dipole allowed transition; anda nonlinear susceptibility associated with the first dipole allowed transition;a source of a valving electric field coupled to a region of the insulator, the valving electric field comprising:a first frequency corresponding to a photon energy smaller than the bandgap and any in gap energy corresponding to a second dipole allowed transition within the bandgap; anda magnitude selected for driving a virtual transition between the first state and the second state under Floquet conditions that increase the bandgap by an amount proportional to a square of the magnitude; anda computer and/or control circuit810controlling a timing of the valve electric field806, a pulse length204of the valve electric field, the magnitude205(e.g. amplitude), and a pulse envelope206of the valve electric field so as to coherently control a response of the region of the insulator to a probe electric field, the response controlled with a temporal resolution equal to the pulse length and matching the pulse envelope.30 A system, device, or method of any of the examples 1-26 utilizing or comprising the circuit, method or valve of any of the examples 27-29.

Advantages and Improvements

The ability to widely tune the optical nonlinearity of a material with ultrafast speed is crucial for advancing photonics technologies spanning optical signal processing, on-chip nonlinear optical sources and optical computing. However, the nonlinear optical properties of materials, dictated by their electronic and crystallographic structures, are largely set at the synthesis and fabrication stages. Further in situ tuning may be achieved by changing the temperature, pressure15, electric field16, current density17,18or carrier concentration19,20, but these approaches are static and often materials specific. Dynamical tuning based on light-induced phase transitions21,22or photocarrier density modulation23have been demonstrated. However, these approaches impart significant heating and are limited in speed owing to electronic and structural relaxation bottlenecks.

Unlike heat based optical valves, the mechanism described herein is completely coherent (i.e., heat free). This means that the duration of this bandgap change is determined by the duration of the light pulse, not requiring any waiting time for trapped heat to dissipate. It also means less wear and tear on the material with repeated use. Embodiments disclosed herein demonstrate that the optical valve can be switched on/off on a time scale faster than 100 femtoseconds, but this is not a fundamental limit (we were limited by the available instrumentation in our laboratory). The magnitude of the pump induced bandgap change depends on the intensity and polarization of the pump light. Moreover, this scheme can in principle to applied to any insulating material. Therefore, optical valves can be made compatible with a wide range of wavelengths using this approach, by choosing a material with the appropriate bandgap and tuning the intensity or polarization of the pump light. Currently, intense optical pumping fields need to be used, but this can be achieved in one or more embodiments using a commercial high power ultrafast laser.

References

Conclusion