RU2120649C1 - Method of commutation and modulation of unidirectional distributively-coupled waves ( versions ) and device for its realization - Google Patents

Abstract

FIELD: fibre-optical communication lines, optical logic circuits. SUBSTANCE: method of commutation and modulation of distributively-coupled waves is realized with the aid of nonlinear optical waveguide manufactured in the form of laminated structure of MQW type with alternating layers that is semiconductor birefrigent and/or optically active, includes lead-in of polarized optical signal emission and polarized optical radiation pumping, changes intensity or phase or polarization or wave length or angle of input of signal emission or simultaneously changes intensities or phases or polarization of pumping radiation and signal emission. Electric current is passed through waveguide in direction transverse to it. Unidirectional distributively - coupled waves are split at output of system. In accordance with another version first radiation of pumping only is input into waveguide and then intensity or polarization or length of radiation wave is changed across input of wave guide or electric or magnetic field applied to waveguide is changed. Device for realization of method includes input-output units, optical element splitting waves across output of waveguide. EFFECT: enhanced compactness and reliability of device, expanded field of its application, decreased pumping power. 49 cl, 7 dwg

Description

 The invention relates to non-linear integrated and fiber optics, and more specifically, to the field of fully optical switches, modulators, and optical transistors and can be used in fiber-optic communication lines, in optical logic circuits, and in other areas where fully optical switching, modulation, and amplification of radiation.

A known method and device for switching and modulating unidirectional distributed-coupled waves [1]. The method consists in switching or modulating emissions propagating in the form of various waveguide modes in a nonlinear waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers. Switching or modulation is achieved by changing the coefficient of energy transfer from one wave to another in a nonlinear medium when the radiation intensity at the input of the waveguide changes. The radiation wavelengths are chosen close to the exciton resonance wavelength λ _r to ensure the maximum cubic nonlinear coefficient of the waveguides. In this method, the transmission of the waveguide at the operating wavelength is small, which is due to the maximum absorption coefficient of the waveguide material at the exciton resonance wavelength. According to the experimental data given in [2], the transmission of the waveguide is 1%. Low transmission and the lack of control over the switching process limits the scope of the method. The disadvantage is the inability to switch and modulate when changing various parameters of the input radiation-polarization, phase, wavelength.

 A device that implements this method includes a nonlinear waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers. Micro lenses are installed at the input and output of the waveguide. In addition to the drawbacks noted above, such an optical switch introduces losses due to drawbacks of the collimating optics at the input and output, which do not take into account the cross-sectional shape of the waveguide. The disadvantages are the difficulty of installing and fixing micro-lenses relative to the waveguide and the lack of compactness of the device.

 Closest to the proposed method and device is a method of switching unidirectional distributed-coupled waves and a device for its implementation [3]. The method includes inputting optical pump radiation and signal radiation of various polarizations into a waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers. Switching is carried out during the interaction of TE and TM waves in a cubic nonlinear medium. When using this method, either large losses occur if the radiation wavelengths are close to the exciton resonance wavelength, or, when choosing a different wavelength, the threshold radiation intensity increases. The disadvantage is the impossibility of switching and modulation when changing various parameters of the input radiation, i.e., the limited scope of the method.

The device for implementing the method comprises a waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers, for example, GaAs / Al _x Ga _1-x As, and an optical element located at the output of the waveguide for separating unidirectional distributed-coupled waves.

 The disadvantages of this device are the inability to control the switching process, the limited scope and large losses due to the lack of collimating optics at the input and output.

 An object of the invention is a sharp decrease in the pump power at the input of the system while increasing the differential gain (i.e. sensitivity of the devices) and the switching depth, as well as achieving compactness and reliability of the device. In addition, an object of the invention is to provide the ability to control the switching process and expand the scope.

In the first variant of the method, the stated problem is solved in that in the method of switching and modulating unidirectional distributed-coupled waves, performed using a nonlinear optical waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers containing at least two heterojunctions, including polarized input optical radiation with an intensity above the threshold into a nonlinear waveguide, and the separation of radiation of various polarizations at the output of the system, a semiconductor The new structure is made of birefringent and / or optically active, and when optical radiation is introduced into the nonlinear waveguide, the intensity, or polarization, or wavelength, or angle of optical radiation input, or external electric or magnetic field applied to the nonlinear waveguide is changed, the length λ radiation waves are selected from the conditions 0.5λ _r ≤ λ ≤ 1.5λ _r , where λ _r is the wavelength of a single-photon and / or two-photon exciton resonance, and an electric current is passed through a nonlinear waveguide.

 In the particular case, radiation of linear, or circular, or elliptical polarization is used.

 In particular, radiation is introduced into the nonlinear waveguide, the polarization of which is directed at an angle π / 4 to the optical axis of the nonlinear waveguide.

 In order to increase the efficiency of radiation input-output, radiation is collimated using a cylindrical lens and / or gradian before radiation is entered into the nonlinear waveguide and / or after the waveguide passes through it, or radiation is introduced into the waveguide and / or radiation output through another optical waveguide, in particular, with on its input and / or output end of the lens.

 To provide modulation of the optical signal with an electric current based on the Faraday effect, the input waveguide is made of magneto-optical material and placed in a solenoid through which an alternating electric current is passed, modulating the radiation polarization, or made in the form of an electro-optical rotator of the plane of polarization.

 In order to ensure the possibility of controllability (in particular, to tune out noise and interference in optical communication lines), an electric current is passed through a semiconductor structure at predetermined time intervals.

In the second variant of the method, the stated problem is solved in that in the method of switching and modulating unidirectional distributed-coupled waves, carried out using a nonlinear optical waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers containing at least two heterojunctions, including polarized input optical signal radiation and polarized optical pump radiation with an intensity above the threshold in the waveguide, and the unidirectional separation of distributed distributed coupled waves at the system output, the semiconductor structure is birefringent and / or optically active, and when signal radiation is introduced into a nonlinear waveguide, the intensity, or phase, or polarization of the signal radiation, or the wavelength, or the angle of input of the signal radiation, is changed, or a simultaneous change in the intensities, or phases, or polarizations of the pump radiation and the signal radiation, while the wavelength λ of the pump radiation and / or signal radiation is selected from the conditions 0.5λ _r ≤ λ ≤ 1,5λ _r , where λ _r is the wavelength of one-photon and / or two-photon exciton resonance, an electric current is passed through the waveguide.

 To switch two or more signal radiations in the logical operation mode “AND”, “OR”, at least one more signal radiation is input at the same time as the signal radiation is input, moreover, the same parameters are variable for all signal radiations.

 In a particular case, the pump radiation may contain radiation of at least two polarizations, or two wavelengths, or two modes.

 In this case, the separation of unidirectional distributed-coupled waves at the output of the system is performed by separation of radiation of various polarizations and / or various wavelengths.

 In the particular case, the signal radiation and the pump radiation are different waveguide modes, and the separation of unidirectional distributed-coupled waves at the output of the system is performed by separation of the radiation of various modes.

 As a rule, the intensity of the pump radiation is at least an order of magnitude greater than the intensity of the signal radiation.

 In the particular case, pump radiation and signal radiation with intensities differing from their geometric mean value by no more than an order of magnitude are used.

 In various special cases of the implementation of the method, it is possible to use pump radiation and signal radiation with both the same and different linear polarization.

 In particular, pump radiation and signal radiation with linear mutually orthogonal polarization are used; one or opposite circular polarizations; the same or different elliptical polarization.

 To increase the efficiency of radiation input and output, radiation is collimated using a cylindrical lens and / or gradan before radiation is entered into the nonlinear waveguide and / or after the waveguide passes through them, or radiation is introduced into the nonlinear waveguide and / or radiation is removed from the waveguide by another optical waveguide, in particular with a lens made on its input and / or output end face.

 To provide modulation of the optical signal with an electric current based on the Faraday effect, the input waveguide contains a Y-connector, one of the input branches of which contains signal radiation, and the other contains pump radiation, while the branch into which signal radiation is supplied is made of magneto-optical material and placed in a solenoid through which an alternating electric current is passed, modulating the polarization of the signal radiation, or is made in the form of an electro-optical rotator of the plane of polarization.

In the particular case of implementation, the carrier frequencies of the signal and the pump differ by an amount greater than t ^-1 , where t is the characteristic time of the signal change.

 In order to ensure the possibility of controllability (in particular, to tune out noise and interference in optical communication lines), an electric current is passed through a semiconductor structure at predetermined time intervals.

 In a particular case, linear polarization radiation is introduced into the nonlinear waveguide, which is directed at an angle π / 4 to the optical axis of the nonlinear waveguide.

 The problem is also solved by the fact that in the device for switching and modulating unidirectional distributed-coupled waves, containing a nonlinear waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers, and an optical element for separating unidirectional distributed-coupled waves at the output of the device, layered the semiconductor structure is made of birefringent or optically active and provided with contacts for passing electric current through the structure in the direction and perpendicular to the layers, the device contains one or two optical input / output elements located respectively at the input and / or output of the nonlinear waveguide, as well as a current source connected to the contacts, the input and / or output elements and the nonlinear waveguide made in in the form of a single module, while the input and / or output elements are installed relative to the nonlinear waveguide with the accuracy provided by their alignment with the luminescent radiation of the semiconductor structure when an electric current.

 In this case, the optical element for separating unidirectional distributed-coupled waves at the output of the device is made in the form of an optical element for separating emissions of various polarizations, or wavelengths, or modes.

In particular, the semiconductor structure is made in the form of alternating layers of GaAs / Al _x , Ga _1-x As or In _1-x , Ga _x As _y P _1-y / GaAs.

 To increase the efficiency of radiation input-output into the waveguide, the input and / or output elements are made in the form of lenses.

 In particular, at least one lens consists of a cylindrical lens and / or gradan.

 In another particular case of the implementation of the method for increasing the efficiency of radiation input-output, the input and / or output elements are made in the form of an additional optical waveguide, in particular with a lens formed on its input and / or output end.

 To combine signal radiation and pump radiation, the device comprises a mixer for pump radiation and at least one signal radiation installed at the input of the device.

 In the particular case of execution, the mixer is made in the form of a waveguide connector, the output branch of which is an input waveguide.

 In particular, the waveguide connector is made in the form of at least one Y-connector or directional coupler.

 To enable the modulation of optical radiation by electric current based on the Faraday effect, one input branch of the waveguide connector is made of magneto-optical material and placed in a solenoid, or made in the form of an electro-optical rotator of the plane of polarization.

 In particular, the input and / or output elements are connected to the waveguide by gluing, or the input and / or output elements are connected to the waveguide by means of a miniature mechanical connector.

 In a particular case, an optical element for separating unidirectional distributed-coupled waves at the system output is designed to separate radiation of different polarizations and is made in the form of a polaroid, or a polarizing prism, or a birefringent prism, or a directional coupler that separates the polarization (for example, in the form of a Glan prism, a waveguide polarizer, film polarizer); in another particular case, it is intended for the separation of radiation of various wavelengths and is made in the form of a dispersion element, or filter, or directional coupler. An optical element for separating unidirectional distributed-coupled waves at the output of the system can be designed to separate the radiation of various modes and is made in the form of a diaphragm or waveguide mode splitter.

 Additionally, a diaphragm and / or quartz cubes can be installed at the input and / or output of the switch.

 In a particular case, the current source is a direct current source.

 In order to ensure the possibility of controllability (in particular, to tune out noise and interference in optical communication lines), the DC source is equipped with a high-speed switch.

 Typically, the device further comprises a laser connected to the input waveguide.

 To enable temperature stabilization, a nonlinear waveguide is soldered to a metal plate located on a Peltier element.

 In FIG. 1 shows a cross section of a waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers; in FIG. 2 and 3 schematically depict device variants for optical switching and modulation with lenses made in the form of a cylindrical lens and gradan; in FIG. 4 - a device for optical switching and modulation using a Faraday cell; in FIG. 5 is an embodiment of a device for optical switching and modulation with input and output waveguides; in FIG. 6 and 7 are versions of a device for optical switching and modulation with inputs for two signal emissions.

 The method of switching unidirectional distributed-coupled waves is carried out by interacting (exchanging energy) waves of different polarizations of the same or different wavelengths in a single birefringent or having an optical activity waveguide. At the same time, signal input and pump radiation are applied to the input of the waveguide in one of the process variants. Signal radiation is a control or information signal; as a rule, the intensity of the signal radiation is at least an order of magnitude lower than the intensity of the pump radiation, however, in some cases the intensities of the indicated radiation can be comparable.

 The signal radiation and the pump radiation can be either different, for example, orthogonal or oppositely directed circular or elliptical polarizations, or one polarization. In the latter case, distributed-coupled waves of various polarizations “born” from the wave of the initial polarization interact inside the waveguide.

 The coefficient of energy transfer from one wave to another depends on the difference in the effective refractive indices of these waves (or on the difference in the phase velocities of these waves) and therefore depends on the radiation intensity at the input of the module, because a non-linear waveguide uses a cubic-nonlinear medium (structure, depicted in figure 1). Thus, when changing, for example, the intensity of the signal radiation and reaching the pump power above the threshold, the radiation switches (i.e., a sharp change in the ratio between the intensities of waves of different polarizations at the output of the nonlinear waveguide), and the amplified signal appears at the output. Due to this change in the ratio of wave intensities, modulation can also be carried out, i.e. introduce information into a coherent wave.

For example, at the input of a birefringent nonlinear optical waveguide with effective refractive indices of ordinary and extraordinary waves n _o and n _e , respectively, and cubic nonlinearity coefficient θ, powerful optical radiation (hereinafter referred to as pumping), characterized by an intensity I _n > 0.1 | n _o -n _e | / | θ |, with a field (polarization) vector directed at an angle π / 4 to the optical axis of the indicated object and linearly polarized optical signal radiation (signal) is simultaneously supplied, maximum intensity which is at least an order of magnitude less than the pump intensity, polarized orthogonally to the pump, and the intensity of this signal is varied from zero to the maximum value. This creates a linear distributed relationship between the signal and the pump, and at the output of the indicated object, the ratio of the intensities of the waves of different polarizations sharply changes. The radiation wavelength, as a rule, is chosen close to the wavelength of the exciton and / or two-photon exciton resonance, because the maximum nonlinear coefficient of the waveguides, and, therefore, provides the most efficient switching. However, the absorption of radiation along the exciton resonance wavelength is maximum. Therefore, an electric current is passed through the waveguide (in the transverse direction), which ensures a decrease in absorption near the resonance absorption region (where the maximum, record-breaking nonlinearity is achieved) by at least an order of magnitude compared with the absence of this current. Due to the transmission of current, the populations of the upper and lower levels approach each other and absorption decreases, and thus the critical intensity and threshold intensity (i.e., the input pump intensity necessary for efficient switching) of the optical radiation introduced into the waveguide sharply decreases.

 Another embodiment of the method can be obtained using non-linear waveguides with optical activity, both natural and artificial.

 You can also switch radiation from one frequency to another. Such switching is carried out in a quadratically nonlinear medium by applying to the input of a nonlinear waveguide, for example, powerful constant pump radiation and weaker signal radiation with a wavelength different from the pump wavelength. Switching the radiation at the output from one frequency to another can also be carried out in a cubic nonlinear medium using several signal radiations with different wavelengths.

 In addition, the modes of pump radiation and signal radiation may vary.

 Switching and modulation of optical radiation can also be carried out under the influence of electric current. For this, the Faraday effect is used (see Fig. 4). At zero current through a solenoid wound on an input waveguide made of magneto-optical glass, the polarization of the field at the output and input of the solenoid, as well as at the entrance to the nonlinear waveguide, is directed along one axis, for example, the vertical axis. When an alternating electric current is passed through a solenoid, the change of which corresponds to a useful alternating signal (analog or digital), the plane of polarization of the optical radiation passing through the input waveguide rotates. The magnitude and sign of the angle of deviation (rotation) of the plane of polarization of optical radiation from the vertical axis (at the output of the Faraday cage) corresponds to the magnitude and sign of the electric current passed through the solenoid, and, therefore, to the magnitude and sign of the useful signal. Since the horizontal component of the field vector at small angles of deviation (rotation) from the vertical is proportional to the angle of deviation (rotation), and the vertical component is almost unchanged, we can assume that the input of a nonlinear waveguide based on MQW receives an alternating signal with a polarization vector directed along horizontal axis, and carrying useful information; simultaneously vertically polarized pumping, almost constant in intensity and almost equal to the input radiation intensity. Under these conditions, the output produces an amplified useful signal.

 Thus, switching and modulation of radiation is achieved not only by changing the intensity at the input of the nonlinear waveguide, but also by changing the polarization, as well as changing the phase difference of the signal radiation and the pump radiation, or changing the radiation frequency, or changing the angle of radiation input into the waveguide, or changing the coupling coefficient between unidirectional distributed-coupled waves or the difference in the effective refractive indices of these waves (for example, due to a change in the birefringence of the waveguide) by position to the waveguide of an electric or magnetic field and its changes.

 In addition, switching or amplification of the modulation can occur when not two different radiations (signal and pump) are applied to the input of the waveguide, but one beam of sufficiently powerful radiation (pump).

 Switching or amplification of the modulation will be achieved with a small input modulation of such radiation in some parameter (intensity or direction of polarization), while at least the maximum values of the input intensity must exceed the threshold.

 For certain values of the radiation intensity at the input of the optical module and a certain value of the current, two switch operation modes can be provided: in the absence of a switching current, there is no switching (there is no radiation at the output), and when current is passed, effective switching occurs (at the same radiation intensity). This creates the ability to control switching modes. Such control can occur by a predetermined program or by a special (service) signal, which is extracted from the information (signal radiation) and sets the boundaries of the time interval during which the signal is to be amplified. At the same time, noise and false signals are cut off.

 Switching can also be carried out using several independent signal radiations, in each of which the same parameters are variable. The choice of the relationship between the magnitude of the signals and the width of the gain section determines the switching mode ("AND" or "OR"). For the AND gate, the magnitude of the signals and the width of the gain section are selected so that switching occurs only if all (or several) signal radiations are present at the input at the same time. Switching in the "OR" mode is carried out for each of the signal radiations received at the input, which is also achieved by choosing the magnitude of the signals and the width of the gain section.

 The optical switching module contains a single waveguide 1, made in the form of the structure shown in figure 1, which can be located on the substrate. The semiconductor structure contains at least two layers. On the upper layer of the semiconductor structure there is one electrical contact 2, on the back surface of the substrate or the lower layer of the structure - another contact 3.

 To ensure optimal conditions for inputting radiation into a nonlinear waveguide and outputting radiation from it, an input lens and an input lens or input and output waveguides are used. The input (output) lens, as a rule, consists of a cylindrical lens 4 and gradan 5, in the focal plane of which a diaphragm 6 can be located. Effective input and output of radiation can be achieved by using additional input waveguides 7, and / or output waveguides 8, having a formed on its input and / or output end face lens 9. The modulation of such radiation by any parameter (intensity or direction of polarization) is carried out by means of a modulator 10.

 In FIG. 2 shows a variant of the device in which only pump radiation is supplied to the input. Modulation or switching is achieved by changing a parameter of the pump radiation.

 In the case of using signal radiation and pump radiation (Fig. 3), a mixer 11 can be used to combine them.

 To separate the radiation of orthogonal polarizations, wavelengths or modes, an optical element 12 is installed at the output. In various embodiments of the device, the optical element 12 for separating radiation has a different implementation. So in a device in which separation of different polarizations is required, element 12 is a polaroid, or a polarizing prism, or a birefringent prism. In the case of using the output waveguides 8, the optical element for separating the various polarizations can be made in the form of a directional coupler that separates the polarization, or a single waveguide, mainly absorbing a wave of one polarization.

 To separate the radiation of different wavelengths, the optical element 12 for separating the radiation is a dispersion element or a filter, for example, an interference one. In this case, the optical element for separating radiation can also be made in the form of a directional coupler (output waveguide 8).

 To separate the radiation of various modes, the optical element 12 for separating radiation may be a mode selection device, made, for example, in the form of a diaphragm. The mode selection device can be made in the form of a waveguide mode splitter (output waveguide 8).

 When the Faraday effect is used in the device, an input waveguide 7 is used, made in this case of magneto-optical glass with a solenoid 13 wound on it. The solenoid can also be wound on one branch 14 of the Y-connector. The solenoid windings are connected to a modulating current source. In ordinary Faraday cells using magneto-optical glass, only a small level of modulation, or low speed, is achieved; in the proposed device, these parameters are many times higher. The input waveguide 7 can be connected to the laser 15, while all the elements of the device and the laser form a single module. The device shown in FIG. 3, allows to achieve a high level of modulation with high speed.

 Embodiments of the device shown in FIG. 6 and 7 are logical elements ("AND" or "OR").

 Electrical contacts 2 and 3 are connected to a direct current source, which can be equipped with a high-speed switch. The switch is tripped either in accordance with a predetermined program, or by a special (service) signal emitted from the signal radiation. In this case, the control input of the switch can be connected to the receiver of the service signal. In addition, the presence of electrical contacts greatly facilitates the alignment of the device and increases its accuracy and reliability, which makes it possible to combine the optical elements of the switch into a single unit. With the passage of current, the multilayer light-bearing structure begins to luminesce, which allows using weak luminescence radiation to install cylindrical lenses and gradients or additional waveguides at the input and output ends of the waveguide, thereby significantly increasing the efficiency of radiation input and output. This also makes it possible to work with collimated cylindrical beams at the input and output of the optical waveguide, and the device itself (optical transistor, modulator, logic element) becomes a ready-made module.

 The possibility of implementing various variants of the method and the execution of the device is illustrated by examples.

Example 1. A pump with a wavelength of λ = 0.83 μm from a semiconductor laser polarized along the vertical axis was passed through a Glan prism, then through a Faraday cell representing a magneto-optical glass doped with terbium (diamagnetic Faraday glass) placed in a solenoid, and then they were introduced into a nonlinear optical waveguide, the light-carrying core of which was made of a layered structure of the GaAs-Al _x Ga _1-x As type, with x = 0.2, representing a set of quantum wells and having birefringence. The optical axis of this birefringent structure was oriented along the vertical axis. The period of the structure was 200 A. The thickness of the light-carrying core was 0.5 μm and approximately 25 periods of the structure were laid on it. The wavelength corresponding to the exciton resonance in this structure was approximately 0.83 μm. Above and below the quantum-well structures are symmetrical horizontal layers of Ga _1-y Al _y As, with y = 0.22 1 .mu.m thick and more (for better waveguide limitation) - layers of Ga _1-y Al _y As, 0.5 microns thick, with y = 0.35. The width of the strip waveguide was 4 μm. The difference in the refractive indices of two orthogonally polarized waves was Δn = 4 × 10 ^-3 . The cross-sectional area is approximately 10 ^-7 cm ² . A weak electric current of the order of 50 mA was passed through the waveguide in a direction perpendicular to the beam (axis of the waveguide). To do this, a film electrode was deposited on top of the waveguide, to which thin metal wires were soldered using thermal compression. The top layer of the semiconductor structure, directly to the film electrode and providing electrical contact, was heavily doped with p ⁺ type GaAs with a carrier concentration of 10 ¹⁹ cm ³ and had a thickness of 0.35 μm. From below, the waveguide was soldered to a metal plate located on the Peltier element. In the region of exciton resonance at the used wavelength, the nonlinear waveguide coefficient was θ = 10 ^-4 GCE. The waveguide length was 600 μm. Input and output of their radiation was carried out using cylindrical lenses and gradans, mounted at the input and output of a nonlinear waveguide. The whole structure containing the input gradan, the input cylindrical lens, the nonlinear waveguide, the output cylindrical lens and the output gradan, had the form of a single module. An alternating electric current was passed through a solenoid, the change of which corresponded to a useful alternating signal (analog or digital). The output received a useful signal amplified by 10 ⁴ times, and the power of orthogonally polarized waves at the system output changed out of phase and the change in each of them was 10 ⁴ times higher than the change in signal intensity at the input of a nonlinear waveguide.

Example 2. Pumping in the form of a sequence of ultrashort pulses with a duration of 10 ps and a wavelength of λ = 1.55 μm from a NaCl: OH laser in the mode synchronization mode, polarized along the vertical axis, was passed through a Glan prism, then through a Faraday cell representing a garnet ferromagnetic crystal (YIG, yttrium-iron garnet), placed in a solenoid, and then introduced into a nonlinear optical waveguide, the light-carrying core of which was made of a layered structure of the type GaAs-Al _x Ga _1-x As, with x = 0.2, representing a set of quantum wells. The period of one pit was 200 A. The thickness of the light-carrying core was 1 μm, and approximately 40 periods of the structure were laid on it. The wavelength corresponding to the exciton resonance in this structure was approximately 0.78 μm. The width of the strip waveguide was 4 μm. The cross-sectional area of about 10 ^-7 cm ² . The difference in the refractive indices of two orthogonally polarized waves was Δn = 4 • 10 ^-3 . A weak electric current of about 70 mA was passed through the waveguide in a direction perpendicular to the beam (axis of the waveguide). To do this, a film electrode was deposited on top of the waveguide, to which thin metal wires were soldered using thermal compression. From below, the waveguide was soldered to a metal plate located on the Peltier element. In the region of two-photon exciton resonance at the used wavelength, the nonlinear waveguide coefficient is θ = 10 ^-11 GCE. The waveguide length was 1 mm. The input and output of radiation from the waveguide was carried out using cylindrical lenses and gradans, mounted at the input and output of a nonlinear waveguide. The entire structure containing the input gradan, the input cylindrical lens, the nonlinear waveguide, the output cylindrical lens and the output gradan had the form of a single module. An alternating electric current was passed through a solenoid, the change of which corresponded to a useful alternating signal (analog or digital). At the output, a useful signal was amplified 10 times, and the powers of orthogonally polarized waves at the system output changed out of phase and each of them changed 10 times the change in signal intensity at the input of a nonlinear waveguide.

Example 3. A pump with a wavelength of λ = 1.3 μm from a semiconductor laser polarized along the vertical axis was passed through a Glan prism, then through a Faraday cell representing a ferromagnetic garnet crystal (YIG, yttrium-iron garnet) placed in a solenoid, and then was introduced into a nonlinear optical waveguide, the light-carrying core of which was made of a layered structure of the type (Fig. 3) In _1-x Ga _x As _y P _1-y / GaAs, with X = 0.2, y = 2.2x, representing a set of quantum wells . The period of the structure was 200 A. The thickness of the light-carrying core was 0.5 μm, and about 20 periods of the structure were laid on it. The wavelength corresponding to the exciton resonance in this structure was approximately 1.3 μm. The width of the strip waveguide was 4 μm. The waveguide is approximately 1 mm long. The difference in the refractive indices of two orthogonally polarized waves was Δn = 4 • 10 ^-3 . The cross-sectional area of about 10 ^-7 cm ² . A weak electric current of about 70 mA was passed through the waveguide in a direction perpendicular to the beam (axis of the waveguide). To do this, a film electrode was deposited on top of the waveguide, to which thin metal wires were soldered using thermal compression. From below, the waveguide was soldered to a metal plate located on the Peltier element. In the region of exciton resonance at the used wavelength, the nonlinear waveguide coefficient was θ = 10 ^-4 GCE. The input and output of radiation from the waveguide was carried out using cylindrical lenses and gradans, mounted at the input and output of a nonlinear waveguide. The entire structure containing the input gradan, the input cylindrical lens, the nonlinear waveguide, the output cylindrical lens and the output gradan had the form of a single module. An alternating electric current was passed through a solenoid, the change of which corresponded to a useful alternating signal (analog or digital). The output received a useful signal amplified by 10 ³ times, and the power of orthogonally polarized waves at the system output changed out of phase and each of them changed 10 ³ times higher than the change in signal intensity at the input of a nonlinear waveguide.

Example 4. We used the lasers and waveguides from examples 1 to 3, but at zero current through the solenoid the polarization of the field at the output and input of the solenoid, as well as at the entrance to the nonlinear waveguide, was directed at an angle of 45 ^o to the vertical axis. The gain of the optical signal and the modulation depth (at the same current amplitude in the solenoid circuit) were approximately an order of magnitude smaller.

Example 5. We used a strip optical waveguide based on a quantum-dimensional layered GaAs / Al _x Ga _1-x As structure with a value of x = 0.2. The period of the structure was 200 A. The thickness of the GaAs layers was 100 A. The thickness of the light-carrying waveguide layer was 1 μm and 50 periods of a quantum-well structure were laid on it. The width of the strip waveguide was 4 μm. The waveguide is approximately 1 mm long. The wavelength corresponding to the edge of the absorption zone was approximately 0.85 μm. Radiation with a wavelength of λ = 0.86 mm from a semiconductor laser was introduced into the waveguide using a cylindrical lens and gradan. Before entering a nonlinear waveguide, this radiation was given circular polarization (for example, by passing through a quarter-wave plate or through an optical waveguide to which an electrical voltage was applied). The radiation was also removed from the waveguide by a cylindrical lens and gradan. Moreover, the entire structure, consisting of an optical waveguide, input and output cylindrical lenses and gradans, was designed as a single module. An electric current of the order of 100 mA was passed through an optical waveguide in a transverse ray (waveguide) in the direction (vertical), due to which the absolute value of the population difference between the valence band and the conduction band decreased and, accordingly, the resonance absorption of radiation sharply decreased. At the same time, due to the proximity to the resonance, a very large nonlinear coefficient of waveguides of the order of 10 ^-4 GGE was achieved. The critical pump power, near which the effective self-switching of radiation occurred, was of the order of 10 mW. A small change in the signal power at the input of the order of 1 μW caused a thousandfold stronger change in the power at the output of the waveguide of the order of 1 mW, and the power at the output of the waveguide in orthogonal polarizations changed in antiphase. The total power at the output and input of the waveguide was approximately the same, which confirms the fact of a sharp decrease in absorption. It should be noted that the radiation of a semiconductor laser used as a pump was formed into a collimated axially symmetric beam using a cylindrical lens and gradan.

 Example 6. The same optical waveguide was used, through which an electric current of the order of 100 mA was passed in the transverse direction. The radiation to the waveguide was fed through an optical fiber waveguide, from which this radiation was introduced into the waveguide through an optical contact. The left circular polarization signal was applied to the waveguide, and the right circular polarization was pumped. At the input, the pump power was 10 mW, and the signal power was about 1 μW, and the input power of the signal was changed by about 1 μW. The change in power at the output of the waveguide was 1 mW.

 Example 7. The same optical waveguide was used, through which an electric current of the order of 50 mA was passed in the transverse direction. The radiation to the waveguide was fed through an optical fiber waveguide, from which this radiation was introduced into the waveguide through an optical contact. A signal of one linear polarization was applied to the waveguide, and a pump of another linear polarization orthogonal to the signal polarization was pumped. The input pump power was 10 mW, and the signal power was about 1 μW, and the power at the output of the waveguides was 1 mW.

 Example 8. The same optical waveguide was used, through which an electric current of about 50 mA was passed in the transverse direction. The radiation to the waveguide was fed through an optical fiber waveguide, from which this radiation was introduced into the waveguide through an optical contact. Radiation of one circular polarization with a power of about 10 mW was supplied to the waveguide, and its input intensity was varied by an amount of the order of 1 μW. The maximum change in power at the output of the waveguide in the left and right circular polarizations was 1 mW and occurred in antiphase.

Example 9. We used a strip optical waveguide based on a quantum-sized layered structure In _1-x Ga _x As _y P _1-y with a value of x = 0.2. The period of the structure was 200 A. The thickness of the GaAs layers was 100 A, and 50 periods of the structure fit the entire thickness of the waveguide (vertically) equal to 1 μm. The width of the strip waveguide was 4 μm. The waveguide was approximately 1 mm long. The wavelength corresponding to the edge of the absorption zone was approximately 1.3 μm. Radiation with a wavelength of λ = 1.3 μm from a semiconductor laser was introduced into the specified waveguide using a cylindrical lens and gradan. The radiation was also removed from the waveguide by a cylindrical lens and gradan. At the same time, the entire structure, consisting of an optical waveguide, input and output cylindrical lenses and gradans, was designed as a single module. An electric current of the order of 70 mA was passed through the waveguide in the transverse ray direction (vertical), due to which the absolute value of the difference between the populations of the valence band and the conduction band decreased and, accordingly, the resonance absorption of radiation sharply decreased. At the same time, due to the proximity to the resonance, a very large nonlinear coefficient of waveguides of the order of 10 ^-4 GGE was achieved. The critical pump power near which there was an effective self-switching of radiation was of the order of 20 mW. A small change in the signal power at the input of the order of 1 μW caused a thousand times stronger change in the power in each polarization at the output of the waveguide (about 10 mW), and the power at the output of the waveguide in orthogonal polarizations changed in antiphase. The total power at the output and input of the waveguides was approximately the same, which confirms the fact of a sharp decrease in absorption. It should be noted that the radiation of a semiconductor laser used as a pump was formed into a collimated axially symmetric beam using a cylindrical lens and gradan.

 Example 10. The optical waveguide of Example 2 was used, through which an electric current of the order of 100 mA was passed in the transverse direction. The waveguide was pumped with a wavelength close to 1.7 μm of linear, or circular polarization, or elliptical polarization, and a signal of another or the same linear, or circular polarization, or elliptical polarization with a wavelength close to 0.85 μm. The input pump power was 50 mW, and the signal power was about 1 μW, and the signal power was changed by a value of about 1 μW. The change in power at the output of the waveguides was 5 mW.

Example 11. A pump with a power of about 60 mW with a wavelength of λ = 0.78 μm from a semiconductor laser polarized along the vertical axis was introduced into a nonlinear optical waveguide, the light-carrying core of which was made of a layered structure of the GaAs-Al _x Ga _1-x As type, with x = 0.3, representing a set of quantum wells. The period of the structure was 200 A. The thickness of the light-carrying core was 0.5 μm and approximately 25 periods of the structure were laid on it. The wavelength corresponding to the exciton resonance in this structure was approximately 0.77 μm. The width of the strip waveguide was 4 μm. The waveguide is approximately 1 mm long. The difference in the refractive indices of two orthogonally polarized waves was Δn = 4 • 10 ^-3 . The cross-sectional area is approximately 10 μm. A weak electric current of the order of 50 mA was passed through the waveguide in a direction perpendicular to the beam (axis of the waveguide). For this, a film electrode was deposited on top of the waveguide, to which thin metal wires were soldered using thermal compression. From below, the waveguide was soldered to a metal plate located on the Peltier element. In the region of exciton resonance at the used wavelength, the nonlinear waveguide coefficient was 10 ^-4 GCE. The waveguide length was 1 mm. The input and output of radiation from the waveguide was carried out using cylindrical lenses and gradans, mounted at the input and output of a nonlinear waveguide. The entire structure containing the input gradan, the input cylindrical lens, the nonlinear waveguide, the output cylindrical lens and the output gradan had the form of a single module. If at the same time a signal modulated in intensity with a wavelength λ = 1.55 μm and a maximum power of 0.5 mW, polarized orthogonally pumped, is introduced into the same nonlinear waveguide using a mixer, then amplified radiation (with a power of the order of 50 mW) with a length of waves λ = 1.55 μm, the modulation of which almost without distortion repeats the modulation of the signal radiation at the input, and the maximum power is 40 mW. In the absence of signal radiation at the input, there is no radiation with a wavelength of λ = 1.55 μm. If the signal radiation at the input has its power of 0.5 mW, then the output power of the radiation with a wavelength of λ = 1.55 μm is 40 mW. In this example, the parametric frequency down conversion is considered, i.e. frequency division. It is based on the quadratic nonlinearity of the medium, which, like cubic nonlinearity, sharply increases near the exciton resonance. Moreover, in this example, the pump falls into the region of exciton resonance, and the signal radiation falls into the region of two-photon exciton resonance.

 To increase the birefringence of the layered structure in order to increase the efficiency of frequency conversion and switching by improving the phase matching of waves at different frequencies ((ω and 2ω)), one can use the GaAs / AlAs structure in which AlAs layers are converted into oxide layers with a refractive index of n ≈ 1.6.

 Example 12. A nonlinear waveguide was used, similar to that considered in example 1, but with twice the thickness of the light-carrying layer. Therefore, two transverse modes could propagate in this waveguide. The input in the Y-mode was pumped in the zero mode and the signal in the first mode. At the output, the radiation of the zero and first modes were spatially separated. A linear connection between the modes can be present (due to spatial heterogeneity [4], but it can be absent. In both the first and second cases, switching between the modes and amplification of the input modulation occurs when the pump exceeds the threshold value.

 Example 13. A nonlinear semiconductor waveguide was used, similar to that described in Example 1. Signal radiation is passed through a phase modulator, which is a waveguide, on the sides of which there are film electrodes, to which a modulating voltage is applied, which changes the phase shift between the signal and the pump linear waveguide inlet. The indicated phase modulator is shown, for example, in Fig. 4.5 (on p. 213) from the book [4].

 Example 14. A nonlinear semiconductor waveguide was used, similar to that considered in Example 1. A stationary spatially periodic along electric field is applied to the waveguide, generated using a periodic electronic structure (see Fig. 4.26 on p. 256, 257 from [4]). In linear mode, a rotation of the plane of polarization occurs in such a structure. In the nonlinear mode (when the threshold is exceeded by pumping) and a small change in the input signal or pump intensity, the radiation sharply switches from TE polarization to TM polarization or vice versa, accompanied by a sharp increase in output modulation.

Literature:
1. P. Li. Kam Wa, PNRobson, JSRoberts, MAPate, JPRDavid. All-optical switching between modes of a GaAs / GaAlAs multiple quantum well waveguide Appl.Phys.Lett. v. 52, No. 24, 2013-2014, 1988.

 2. PCT Application No. 96/01441, CL G 02 F 1/01, 1996.

 3. Wave optoelectronics. Ed. T. Tamira, M., Mir, 1991.

 4. R. Jin. , C. L. Chuang, H.M. Gibbs, S.W. Kohh, J.N. Polky, G.A. Pubans "Picosecond all-optical switching in single-mode GaAs / AlGaAs strip-loaded nonlinear directional couplers", Appl.Phys. Lett., 53 (19), 1977, p. 1791-1792.

Claims (49)

1. The method of switching and modulation of unidirectional distributed-coupled waves, carried out using a nonlinear optical waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers containing at least two heterojunctions, including the input of polarized optical radiation with an intensity above the threshold into the nonlinear waveguide , and separation of radiation of various polarizations at the output of the system, characterized in that the semiconductor structure is birefringent general and / or optically active, and when optical radiation is introduced into a nonlinear waveguide, the intensity, or polarization, or wavelength, or angle of optical radiation or external electric or magnetic field applied to the nonlinear waveguide is changed, while the radiation wavelength λ choose from the conditions 0.5λ _r ≤λ≤1.5λ _r , where λ _r is the wavelength of a single-photon and / or two-photon exciton resonance, and an electric current is passed through a nonlinear waveguide.  2. The method according to claim 1, characterized in that they use the radiation of linear, or circular, or elliptical polarization.  3. The method according to claim 2, characterized in that radiation is introduced into the nonlinear waveguide, the polarization of which is directed at an angle π / 4 to the optical axis of the nonlinear waveguide.  4. The method according to any one of claims 1 to 3, characterized in that before the radiation is introduced into the nonlinear waveguide and / or after the radiation waveguide passes through it, the radiation is collimated using a cylindrical lens and / or gradan.  5. The method according to any one of claims 1 to 3, characterized in that the input of radiation into the nonlinear waveguide and / or output of radiation from the waveguide is carried out by means of an input and / or output optical waveguide.  6. The method according to claim 5, characterized in that the lens is made at the input and / or output end of the input and / or output optical waveguide.  7. The method according to p. 5, characterized in that the input waveguide is made of magneto-optical material and placed in a solenoid through which an alternating electric current is passed, modulating the radiation polarization, or made in the form of an electro-optical rotator of the plane of polarization.  8. The method according to any one of claims 1 to 7, characterized in that the electric current is passed through the semiconductor structure at predetermined time intervals. 9. The method of switching and modulation of unidirectional distributed-coupled waves, carried out using a nonlinear optical waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers, containing at least two heterojunctions, including the input of polarized optical signal radiation and polarized optical pump radiation with intensity above the threshold in a nonlinear waveguide, and the separation of unidirectional distributed-coupled waves at the output of the system, from characterized in that the semiconductor structure is birefringent and / or optically active, and when the signal radiation is introduced into the non-linear waveguide, a change in intensity, or phase, or polarization, or wavelength, or angle of input of signal radiation, or a simultaneous change in intensities or phases, or polarizations of pump radiation and signal radiation, pump radiation and / or signal radiation are selected from the conditions 0,5≤λ _r ≤1,5λ _r, where λ _r - wavelength-photon and / or two-photon exciton D onansa through nonlinear waveguide electric current is passed.  10. The method according to claim 9, characterized in that at the same time as the input of the signal radiation, at least one more signal radiation is input, and all signal radiations have the same parameters.  11. The method according to claim 9 or 10, characterized in that the pump radiation contains radiation of at least two polarizations, or two wavelengths, or two modes.  12. The method according to any one of claims 9 to 11, characterized in that the separation of unidirectional distributed-coupled waves at the output of the system is carried out by separating emissions of different polarizations and / or different wavelengths.  13. The method according to any one of claims 9 to 11, characterized in that the signal radiation and the pump radiation are different waveguide modes, and the separation of unidirectional distributed-coupled waves at the output of the system is carried out by separating the radiation of various modes.  14. The method according to any one of claims 9 to 13, characterized in that the intensity of the pump radiation is at least an order of magnitude greater than the intensity of the signal radiation.  15. The method according to any one of claims 9 to 13, characterized in that they use pump radiation and signal radiation with intensities that differ from their geometric mean value by no more than an order of magnitude.  16. The method according to any one of claims 9 to 15, characterized in that they use pump radiation and signal radiation with the same or different linear polarization.  17. The method according to clause 16, characterized in that the use of pump radiation and signal radiation with linear mutually orthogonal polarization.  18. The method according to any one of claims 9 to 15, characterized in that they use pump radiation and signal radiation of one or opposite circular polarizations.  19. The method according to any one of claims 9 to 15, characterized in that they use pump radiation and signal radiation of the same or different elliptical polarization.  20. The method according to any one of claims 9 to 19, characterized in that before the radiation is introduced into the nonlinear waveguide and / or after the radiation waveguide passes through them, the radiation is collimated using a cylindrical lens and / or gradan.  21. The method according to any one of paragraphs.9 to 19, characterized in that the input of radiation into a nonlinear waveguide and / or output of radiation from the waveguide is carried out by means of an input and / or output optical waveguide.  22. The method according to item 21, wherein the lens is made at the input and / or output end of the input and / or output optical waveguide.  23. The method according to item 21, wherein the input waveguide contains a Y-connector, signal radiation is supplied to one of the input branches, and pump radiation is supplied to the other, the branch to which signal radiation is supplied is made of magneto-optical material and placed in a solenoid through which an alternating electric current is passed, modulating the polarization of the signal radiation, or is made in the form of an electro-optical rotator of the plane of polarization. 24. The method according to any one of claims 9 to 23, characterized in that the carrier frequency of the signal radiation and the pump radiation differ by an amount greater than t ^-1 , where t is the characteristic time of the signal change.  25. The method according to any one of claims 9 to 24, characterized in that the electric current is passed through the semiconductor structure at predetermined time intervals.  26. The method according to any one of claims 9 to 25, characterized in that radiation is introduced into the nonlinear waveguide, the polarization of which is directed at an angle π / 4 to the optical axis of the nonlinear waveguide.  27. A device for switching and modulating unidirectional distributed coupled waves, comprising a nonlinear waveguide made in the form of a layered semiconductor structure of the MQW type with alternating layers containing at least two heterojunctions, and an optical element for separating unidirectional distributed coupled waves at the output of the device, characterized in that the layered semiconductor structure is made of birefringent or optically active and provided with contacts for passing electric current through without a structure in the direction perpendicular to the layers, the device contains one or two optical input / output elements located respectively at the input and / or output of a nonlinear waveguide, as well as a current source connected to the contacts, the input and / or output elements and nonlinear the waveguide is made in the form of a single module, while the input and / or output elements are mounted relative to the nonlinear waveguide with the accuracy provided by their alignment with the luminescent radiation of the semiconductor structure during transmission electric current through it.  28. The device according to item 27, wherein the optical element for separating unidirectional distributed-coupled waves at the output of the device is made in the form of an optical element for separating emissions of different polarizations or wavelengths.  29. The device according to item 27, wherein the optical element for separating unidirectional distributed-coupled waves at the output of the device is made in the form of an optical element for separating emissions of various modes. 30. The device according to item 27, wherein the semiconductor structure is made in the form of alternating layers of GaAs / Al _x Ga _1-x As or In _1-x Ga _x As _y P _1-y / GaAs.  31. The device according to any one of paragraphs.27-30, characterized in that the input and / or output elements are made in the form of lenses.  32. The device according to p, characterized in that at least one lens consists of a cylindrical lens and / or gradan.  33. The device according to any one of paragraphs.27-30, characterized in that the input and / or output elements are made in the form of an input and / or output optical waveguide.  34. The device according to p. 33, wherein a lens is formed on the input and / or output end of the input and / or output optical waveguide.  35. The device according to any one of paragraphs.27 to 34, characterized in that it further comprises a mixer for pump radiation and at least one signal radiation mounted at the input of the device.  36. The device according to clause 35, wherein the mixer is made in the form of a waveguide connector, the output branch of which is an input waveguide.  37. The device according to clause 36, wherein the waveguide connector is made in the form of at least one Y-connector or directional coupler.  38. The device according to clause 37, wherein one input branch of the waveguide connector is made of magneto-optical material and placed in a solenoid, or made in the form of an electro-optical rotator of the plane of polarization.  39. The device according to any one of paragraphs.27 to 38, characterized in that the input and / or output elements are connected to a non-linear waveguide by gluing.  40. The device according to any one of paragraphs.27 to 38, characterized in that the input and / or output elements are connected to the waveguide via a miniature mechanical connector.  41. The device according to any one of paragraphs.27-40, characterized in that the optical element for separating radiation of different polarizations is made in the form of a polaroid, or a polarizing prism, or a birefringent prism, or a directional coupler that separates the polarization.  42. The device according to any one of paragraphs.27-40, characterized in that the optical element for separating emissions of different wavelengths is made in the form of a dispersion element, or a filter, or a directional coupler.  43. The device according to any one of paragraphs.27 - 40, characterized in that the optical element for separating the radiation of various modes is made in the form of a diaphragm or waveguide splitter mode.  44. The device according to any one of paragraphs.27 to 42, characterized in that a diaphragm is installed at the input and / or output of the nonlinear waveguide.  45. The device according to any one of paragraphs.27 to 42, characterized in that a quartz cube is installed at the input and / or output of the device.  46. The device according to any one of paragraphs.27 to 45, characterized in that the current source is a constant current source.  47. The device according to item 46, wherein the constant current source is equipped with a high-speed switch.  48. The device according to any one of paragraphs 33 to 47, characterized in that it further comprises a laser connected to the input waveguide.  49. The device according to any one of paragraphs.27 to 48, characterized in that the non-linear waveguide is soldered to a metal plate located on the Peltier element.

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