Optical phased array, laser assembly, and method for operating same

Abstract

The invention relates to an optical phased array having a signal input for supplying useful light of a first wavelength, and to a first modulation input for supplying modulation light of a second wavelength. A first waveguide array, having at least one signal output, is connected to the signal input and comprises a material that is transparent to the useful light and has a first band gap. A second waveguide array connected to the first modulation input is arranged in the vicinity of the first waveguide array and designed to guide modulation light onto the first waveguide array, wherein the first band gap is smaller than the energy of the modulation light.

Description

[0001] OPTICAL PHASE ARRAY, LASER ARRAY AND METHOD FOR OPERATING ONE

[0002] OF SUCH

[0003] The present invention claims the priority of the German first application DE 10 2022 109 220 . 8 of April 14, 2022, the disclosure content of which is hereby incorporated in its entirety by reference.

[0004] The present invention relates to an optical phased array, a resonator arrangement, and a laser arrangement comprising the optical phased array or the resonator arrangement. The invention further relates to a method for operating an optical phased array or a resonator arrangement.

[0005] BACKGROUND

[0006] Edge-emitting lasers are based on laser diodes and are now available across a wide frequency spectrum. Their high output power and mass production have made them interesting for a wide range of applications. In addition to edge-emitting lasers, VCSELs or pLEDs with a small etendue can also be used to couple the light into a waveguide. These are generally referred to as optoelectronic components.

[0007] Such optoelectronic components are characterized by a larger linewidth in the range of a few nanometers, with the output frequency also varying depending on the current and temperature. While this opens up a tuning option, it also influences the laser's output power, necessitating increased circuit complexity to compensate for or suppress unwanted effects.

[0008] However, in a number of applications, lasers with narrow linewidths or high stability of the emission wavelength and power are desired. For this, edge-emitting lasers must be stabilized. One way to achieve this is by using DBR structures along the laser resonator, although this is associated with increased costs. An alternative is to couple the laser arrays to external cavities with adjustable etalons, Bragg gratings, or even small-form-factor microresonators.

[0009] In all of these, line widths of only a few kHz can be achieved.

[0010] In other applications, the focus is on the ability to align a light beam, i.e. to cover a defined field of view with a previously defined resolution. Examples of such applications include RGB projections and LIDAR. This can be achieved using a component that expands the laser beam in order to cover a high-resolution LCD, SLM (Spatial Light Modulator) or DLP display. Alternatively, a laser beam or a light beam can be redirected using movable mirrors, either as MEMS or even macromechanical types. Neither technology is an ideal compromise: pixel array projections are less efficient and lack contrast and brilliance, while mechanically movable elements often lead to problems with robustness and increased complexity.

[0011] There is therefore a need for non-mechanical beam steering or scanning options that can be easily integrated into a housing and thus enable a significant reduction in the installation volume.

[0012] SUMMARY OF THE INVENTION

[0013] This need is met by the subject matter of the independent patent claims. Further developments and embodiments of the proposed principle are specified in the subclaims.

[0014] For this purpose, the inventors propose optical phased arrays (OPAs) that are optically controlled and enable large modulation bandwidths in very small form factors. In addition to optical phased arrays, other optical components such as resonators, modulators, or even optical switches can also be controlled very quickly and wear-free using the proposed principle.

[0015] In particular, in an optical component of the type mentioned above, the inventors take advantage of the fact that the refractive index can be influenced, among other things, by free charge carriers. For example, an optical component can have a transparent semiconductor material in which free charge carriers are generated by absorbing photons with an energy higher than the band gap. These photons are provided via what is known as modulation light. The photon flux is the basis for active modulation of the optical component and can be provided, for example, by a second planar waveguide component located underneath and / or above, which directs the modulation light onto the optical component to be modulated.

[0016] This results in a modulation of the refractive index, with the modulation speed being essentially limited by the lifetime of the charge carriers in the material. Especially in optical phased arrays in the narrower sense, this provides a waveguide ensemble tailored to the desired phase-shift function. A high-frequency intensity-modulated control laser or a laser diode (or possibly several of them) provides the required photon flux.

[0017] In some aspects of the principle presented here, an optical phased array is proposed. The term "optical phased array" should not be understood in a narrow sense. Rather, it includes a component whose optical behavior can be adjusted in a desired manner by changing the refractive index. The change in the refractive index is achieved by another element of the phased array, which deflects a modulation light so that it generates charge carriers through absorption, which change the refractive index. Possible components of this type, whose refractive index can be advantageously adjusted, include optical phased arrays in the narrow sense, i.e. with several waveguides of different lengths, optical resonators, in particular ring oscillators, Mach-Zehnder modulators or directional optical couplers, to name a few.

[0018] The adjustable optical phased array comprises a signal input for supplying useful light of a first wavelength and a first modulation input for supplying modulation light of a second wavelength. A first waveguide array is connected to the signal input and comprises at least one signal output and a material which is transparent to the useful light and has a first band gap. A second waveguide array is connected to the first modulation input and arranged in the vicinity of the first waveguide array such that modulation light can be guided onto the first waveguide array. The first band gap is smaller than the photon energy of the modulation light. In other words, the material of the first waveguide array is selected such that it absorbs light of the second wavelength to form charge carriers.The term waveguide array is also not overly narrow in the above-mentioned broader understanding of an optical phased array, but rather should be understood as an optical component that is intended to provide a certain functionality.

[0019] In this context, the first and second waveguide arrays can have the same or at least a similar shape. In particular, the second waveguide array should be designed such that it can effectively redirect the modulation light onto the first waveguide array, i.e. the first component whose refractive index is to be changed. Accordingly, in some aspects it is provided that the first waveguide array and the second waveguide array are arranged one above the other in two essentially parallel planes and additionally overlap in some areas. The overlap increases efficiency because the modulation light can shine better into the first waveguide array. The waveguides of the second waveguide array are matched to the first waveguide array such that the desired change in refractive index occurs in the individual waveguides of the first array at a predetermined intensity of the modulation light.

[0020] The intensity of the modulation light can be used to adjust the rate of charge carrier generation and thus modulate the refractive index in the first waveguide array. The modulation can be carried out digitally, e.g. by a pulsed modulation signal, but also as an amplitude-modulated signal. In some aspects, the first waveguide array of the optical phased array comprises a plurality of waveguides which lie essentially in one plane and have a defined light propagation time difference from one another. This can be achieved, for example, by a different length of the waveguides. The light propagation time difference results in a phase difference at the output of the array and thus a superposition and thus an interference. By modulating the refractive index according to the proposed principle, the phase difference is controllable so that a light beam emitted by the array can be controlled.

[0021] In a further aspect, the second waveguide array also comprises a plurality of waveguides that lie essentially in one plane and have a defined light propagation time difference. This can also be implemented with waveguides of different lengths.

[0022] In a further aspect, the optical phased array comprises a further second modulation input for supplying modulation light of the second or a third wavelength. The modulation light of the third wavelength also has a higher energy than the band gap of the material of the first waveguide array, such that absorption occurs with the generation of free charge carriers. The second modulation input is connected to a third waveguide array and arranged in the vicinity of the first waveguide array such that modulation light can be guided onto the first waveguide array. In this way, increased flexibility is achieved and, in addition, the range of refractive index modulation is increased by charge carrier generation. At this point, it is possible to arrange the first waveguide array between the second and the third waveguide array and thus to direct modulation light from both sides onto the first waveguide array.Depending on the design, the second and third waveguide arrays can either overlap or be arranged in a mirror image of one another. In a further aspect, the second and / or third waveguide array comprises an output coupling structure, in particular in the form of a diffractive optic. This serves to couple the modulation light out of the waveguide array in a defined manner. The diffractive optic or the output coupling structure can also guide the light and thus guide the modulation light to the first waveguide. In some designs, the output coupling structure faces the first waveguide array. The output coupling structure allows a definable part of the modulation light to be coupled out in a spatially localized manner.In an alternative embodiment, the second and / or third waveguide array are only slightly spaced from the first waveguide array, for example, less than 300 nm and in particular less than 100 nm. As a result, a portion of the light (a portion of the light field) enters the first waveguide array as evanescent light. For example, the waveguide arrays can also be so close to one another that crosstalk of the modulated light into the first waveguide array occurs.

[0023] Another aspect deals with improving the coupling of the modulation light into the first waveguide array. In one aspect, a particularly planar DBR structure is provided, which is arranged on the side of the first waveguide array opposite the second waveguide, in particular for the back reflection of modulation light. As a result, modulation light can either be absorbed or reflected back. In a further embodiment, it is conceivable to provide a planar distribution layer, which is arranged on the side of the first waveguide opposite the second waveguide and is designed to reflect modulation light back or to distribute charge carriers generated by modulation light in the first waveguide array. A uniform distribution of the charge carriers is useful in order to produce a uniform change in the refractive index.

[0024] Some aspects deal with a suitable selection of materials. In some aspects, a semiconductor material is used as the material of the first waveguide array. This can have a direct or an indirect band gap, which is chosen such that it is essentially transparent to the useful light. In one aspect, the material comprises InP, Si, GaAs, AlGaAs, AlGaP or GaN. In contrast, these materials are not transparent to the light of the second wavelength; the modulation light is therefore absorbed in the material with the generation of charge carriers. However, the material of the second or even the third waveguide array should be transparent to the modulation light. It follows that it generally has a higher band gap than the material of the first waveguide array. Possible materials that can also be matched to the material of the first waveguide array would be AlN, SiNx, Al2O3 or SiO2.

[0025] In some aspects, a resonator arrangement is proposed which comprises a waveguide with a signal input for supplying useful light of a first wavelength and a signal output. The arrangement further comprises a resonator, in particular a ring resonator, which is optically coupled to the waveguide in order to amplify a frequency mode of the useful light in the waveguide. An arrangement which is designed to radiate modulation light of a second wavelength into the resonator is placed above the resonator. For this purpose, the resonator is formed from a material with a band gap which is essentially transparent to useful light and absorbs modulation light to form charge carriers. In this way, a tunable resonator arrangement is implemented which enables a particularly mode-stable, but tunable laser.Possible applications for such resonator arrangements are in the field of coherent distance measurement, high-resolution spectroscopy or image projection, for example for AR or VR projections.

[0026] In one embodiment, the arrangement placed above the resonator comprises one or more deflecting mirrors. Alternatively, the arrangement can also have a second waveguide with a diffractive optic that is designed to direct modulation light in the second waveguide onto the resonator. As with the optical phased array, a DBR structure, in particular a planar one, can be provided, which is arranged on the side of the resonator opposite the second waveguide, in particular for reflecting back modulation light. A further aspect relates to a laser arrangement that uses optical components according to the proposed principle. The laser arrangement comprises a first laser device for generating useful light and a second laser device for generating modulation light. The intensity of the modulation light is modulated by the second laser device.The two laser devices are connected to the optical phased array, the optical component or the resonator arrangement.

[0027] A further aspect relates to operating an optical phased array, wherein the phased array comprises a signal input for supplying useful light of a first wavelength and a first waveguide array with at least one signal output, which is connected to the signal input and has a material transparent to the useful light and having a first band gap. In the method, useful light is radiated into the first waveguide array. Likewise, modulation light is generated and at least partially coupled into the first waveguide array. By absorbing the radiated modulation light, charge carriers are generated in the first waveguide array, which change the refractive index in a characteristic manner. The change in the refractive index is controlled by varying the intensity of the modulation light.

[0028] In one aspect, the modulation light is coupled in by means of a second waveguide array which is arranged in the vicinity of the first waveguide array in such a way that modulation light can be guided onto the first waveguide array. Depending on the optical component, the first and second waveguide arrays have different properties and features. In some aspects, the first waveguide array comprises a plurality of waveguides which lie essentially in one plane and have a defined light propagation time difference from one another. The second waveguide array can also be designed in the same way and have a plurality of waveguides which lie essentially in one plane and have a defined light propagation time difference from one another.In some embodiments, the propagation time differences in the waveguides of the first or second waveguide array are formed by different lengths of the waveguides.

[0029] BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Further aspects and embodiments according to the proposed principle will become apparent with reference to the various embodiments and examples which will be described in detail in conjunction with the accompanying drawings.

[0031] Figure 1 shows an embodiment of an optical phase array;

[0032] Figure 2 shows a plan view of a design of a phased array according to the proposed principle;

[0033] Figure 3 is a sectional view of the phased array of Figure 2 showing some aspects of the proposed principle;

[0034] Figure 4 shows a second embodiment of an optical phased array with some aspects of the proposed principle;

[0035] Figure 5 is an alternative embodiment of Figure 4;

[0036] Figure 6 shows the sectional view of the phased array according to Figure 4 or 5 to explain some aspects of the proposed principle;

[0037] Figure 7 shows a sectional view of a further embodiment of a phased array according to the proposed principle;

[0038] Figure 8 shows a further sectional view of an embodiment of a phased array according to the proposed principle;

[0039] Figure 9 is a third embodiment of a phased array incorporating some aspects of the proposed principle;

[0040] Figures 10 to 12 are various sectional views of embodiments of a phased array according to the principle of Figure 9; Figure 13 is an embodiment of a method with some aspects of the proposed principle.

[0041] DETAILED DESCRIPTION

[0042] The following embodiments and examples show various aspects and their combinations according to the proposed principle. The embodiments and examples are not always true to scale. Likewise, various elements can be shown enlarged or reduced in size to emphasize individual aspects. It goes without saying that the individual aspects and features of the embodiments and examples shown in the figures can be combined with one another without thereby impairing the inventive principle. Some aspects have a regular structure or shape. It should be noted that in practice slight deviations from the ideal shape can occur without, however, contradicting the inventive idea.

[0043] Furthermore, the individual figures, features, and aspects are not necessarily shown in the correct size, and the proportions between the individual elements may not always be correct. Some aspects and features are emphasized by being shown enlarged. However, terms such as "top", "above", "below", "below", "larger", "smaller", and the like are correctly represented with reference to the elements in the figures. This makes it possible to infer such relationships between the elements from the illustrations.

[0044] Figure 1 shows the arrangement of a so-called optical phase array in the narrower sense, i.e. an arrangement in which beam shaping can be achieved by means of a phase shift generated by several optical waveguides of different lengths.

[0045] The arrangement comprises an edge-emitting laser 1, for example in the form of a laser diode or alternatively another laser arrangement. An optical phased array 3' is connected to the output of this laser arrangement. This comprises a waveguide 11 connected to the signal input, which further splits into several individual branches 11a, 11b to 11g. Each of these individual branches has a different length and leads to a corresponding signal output 12'.

[0046] When the arrangement is in operation, useful light NL is radiated in and distributed into the various branches 11a to 11g of the optical phase array 3". Due to the different lengths of the individual branches, this leads to signals with a phase shift between one another at the respective outputs 12". These signals interfere with one another. By suitably adjusting the length based on the frequency or wavelength of the scattered useful light, this leads to constructive or destructive interference. The position of the constructive interference on a screen S at the positions PI or P2, shown as an example in Figure 1, can be adjusted using various measures. In general, the position of this constructive interference depends on the geometric parameters and on the refractive index of the waveguides 11a to 11g. The position PI or P2 can be adjusted by changing the refractive index of the material.P2 on the screen S, so that a "scan" of the screen is achieved by means of the interfering output light.

[0047] Conventional methods use, for example, a thermal process in which the optical phased array 3" is heated or cooled, whereby the respective refractive index of the waveguide changes in a characteristic manner. However, such a process is relatively slow and can only be controlled to a limited extent. Alternatively, it is also possible to change the refractive index in the individual regions by applying a constant electric field. Although this is an improvement over a thermal process, it requires relatively high voltages to create the necessary electric field. This approach is therefore rather complex to implement, especially in applications with low available operating voltages.

[0048] Figure 2 shows an embodiment of the proposed principle in which the refractive index of the optical component is not adjusted using a thermal or electro-optical process, but rather by means of a purely optical process. This takes advantage of the fact that the material of the waveguides 11a to 11g, i.e. the material of the optical component 3, also has a band gap and can therefore also absorb light. Although the waveguides 11a to 11g are transparent to the useful light, photons with higher energies can be absorbed in the waveguides and thus generate free charge carriers. These free charge carriers then bring about a change in the refractive index in a characteristic manner. Figure 2 now shows a possible embodiment of this principle.

[0049] The arrangement according to the proposed principle comprises an optical component 3, which in the present case is also designed as an optical phased array in the narrower sense. A laser device 1 is arranged at a signal input, which in turn is coupled to a waveguide 11. This can be an edge-emitting laser, a laser diode or also a laser device not based on semiconductor structures. The optical phased array comprises a plurality of waveguides 11a, 11b to 11g which are connected to one another on the input side and each lead to a signal output 12' on the output side. The length of the respective waveguides between the signal input and signal output is different and matched to one another in such a way that an interference pattern of incident light is produced at the output on a screen in a similar way to that in Figure 1.

[0050] According to the invention, the optical component 3 now comprises a second signal input, which in turn is connected to a second laser diode 2 for supplying a modulation light ML. This modulation input is in turn connected to a plurality of waveguides 21a, 21b to 21g. The waveguides also form a waveguide structure for the modulation light ML and are designed such that the individual waveguides 21a, 21b to 21g lie over a portion of the waveguides 11a, 11b to 11g.

[0051] In this regard, Figure 3 shows a sectional view of the arrangement according to the proposed principle. It can be seen here that the individual waveguides 11a, 11b to 11g for the useful light NL are arranged essentially along one plane. Above this plane, also in one plane, are the waveguide structures 21a, 21b to 21g for the modulated light ML. Each of these waveguides 21a, 21b to 21g of the structure for the modulated light ML has an output coupling optic 22 facing the respective waveguide 11a, 11b to 11g.

[0052] During operation of the proposed arrangement, a modulation light ML is radiated whose photon energy is greater than the band gap of the material in the waveguides 11a, 11b to 11g. For the sake of simplicity, it is assumed here and in the following for the explanation of the inventive principle that the band gap is constant and that it makes no distinction with regard to crystal direction or direct / indirect band gap. Indeed, the present principle is possible when light is absorbed in the material of the waveguide or in the surrounding area, which then generates free charge carriers in the material of the waveguide.

[0053] The modulation light ML exits through the existing output optics and is optically absorbed by the waveguides 11a, 11b to 11g. As a result of the absorption, charge carriers are generated in the conduction band of the material of the waveguides 11a, 11b to 11g, as a result of which the refractive index of this material changes. Due to the length of the individual waveguides 21a, 21b to 21g for the modulation light ML, as shown in plan view in Figure 2, there is intensity-dependent irradiation and also a resulting absorption in a predetermined manner, so that a characteristic change in the refractive index occurs in the individual waveguides 11a, 11b to 11g for the useful light NL. A change in the intensity of the modulation light ML also changes the refractive index. An intensity modulation of the light ML thus brings about a characteristic modulation of the refractive index.

[0054] The material of the waveguides for the modulation light ML is selected such that it is transparent to the modulation light ML itself. The energy of the photons of the modulation light ML is so high that it exceeds the band gap of the waveguides 11a to 11g and is thus absorbed by them, generating free charge carriers. By adjusting the intensity of the modulation light, the charge carrier generation and thus also the resulting change in the refractive index can be adjusted or changed. In this way, it is possible to adjust the interference pattern at the output of the optical component 3 and, for example, to achieve the effect shown in Figure 1, namely changing a constructive interference maxima along a position.

[0055] The change in a refractive index based on charge carriers is essentially determined by three effects. Firstly, there is a filling of the density of states or filling of the allowed band states with free charge carriers according to Burstein Moss, which generally leads to a change in the refractive index towards lower values. Band gap normalisation or even a slight change in the band gap towards smaller energies leads to a change in the refractive index towards larger values. Finally, the refractive index in the transparency region of the EM spectrum, which is of interest, can be changed towards smaller values ​​via free charge carrier generation and subsequent characteristic absorption in the IR range. In the proposed principle, these three aspects work together, with free charge carrier absorption according to the Drude model being the main consideration.

[0056] In this process, charge carriers absorb a light particle in the medium, thereby raising them to a higher energy state. Charge carriers within the valence band are raised to the conduction band, forming an electron-hole pair. In this way, freely moving electrons are generated in the conduction band, which act similarly to an eh-plasma. This plasma generates a characteristic absorption band in the IR range, which can be described using the Drude model. Via the so-called Kramers-Kronig relation, this in turn produces a reduction in the refractive index at shorter wavelengths. According to the Drude model, this is represented by formula (1). This results in a change in the refractive index, which essentially depends on the number of negative electrons in the conduction band or holes in the valence band. The values ​​N and P are the free charge carriers, the masses m denote the effective masses of the electrons or holes, but the mass m H of the holes p is significantly larger than the mass of the electrons , so that the term — mh is often negligible .

[0057] The change in refractive index is negative, i.e., the absorption of light within the waveguide reduces the refractive index. Furthermore, the change in refractive index is proportional to the square of the wavelength A, which generally results in a greater change in refractive index at longer wavelengths, i.e., at lower energies.

[0058] In the following, the charge carrier generation for an irradiated modulation light will be estimated and the resulting change in the refractive index will be reproduced at least qualitatively. The modulation light in this estimation is generated by a laser with a power of 100 mW and a beam diameter of d=100 pm. The wavelength of the modulation light is A=400 nm. A combination of InP and GaP is used as waveguide material for the optical component, the parameters used refer to InP. For InP, the refractive index at A=400 nm is equal to n=4.4. GaP, on the other hand, has a refractive index of n=4.2 at A=400 nm. The intensity I is then

[0059] For simplicity, it is assumed that the modulation light is completely absorbed in the material without reflection or loss.

[0060] The intensity of the laser beam decreases exponentially within the material, i.e. the intensity is approximately proportional to e <-z / z0) , where zo is the absorption length . The absorption length corresponds to the length z at which the intensity of the light is reduced to 1 / e (or 1 / e 2 for I ) of the original I . This results in an absorption length of approximately with zo approx. 40 nm

[0061] The decrease in light means that charge carriers have been created there. In this way, the number of charge carriers can be calculated in the absorption length.

[0062] Estimate charge carriers with

[0063] This is therefore in the range of about 10 26 1 / ( scm 3 ) . With an irradiation duration of about 1 ns, n,-„ ; = 6 * 1017 — - are generated .

[0064] The electron-hole plasma thus generated also recombines, causing the number of free charge carriers to decrease. The recombination rate follows various mechanisms. These mechanisms include recombination via direct recombination, i.e., the electron and hole recombine together to produce a corresponding photon, plasmon, or phonon. Alternatively, there is also the possibility of so-called Auger recombination, which, however, is several orders of magnitude lower than direct recombination and can therefore be disregarded.

[0065] The recombination rate R thus results from the concentration n, p of the available charge carriers and a material-dependent parameter C , which characterizes the two mechanisms mentioned above in the respective material.

[0066] R = C * (n * p — n 2 ) ( 4 )

[0067] For an indicated charge carrier density n=p in the range of 6 * 10 17 1 / cm 3 and a parameter C of 6 * IO -11 cm 3 / s , which indicates direct recombination , equation ( 4 ) yields a recombination rate R in the range of 2 * 10 16 1 / nscm 3 . With a roughly constant

[0068] Recombination rate, the generated charge carriers would therefore be completely combined after approximately 10 ns. The generation rate of charge carriers and the recombination rate can also be represented by a differential equation, which is given by dn(t)

[0069] Equation (5) is given. The generation rate thus corresponds to a constant value given by a parameter a, which corresponds to the charge carrier density and can be derived from (3) and the intensity I, which is minus the product of the recombination rate and the number of charge carriers over time. The following applies:

[0070] = al — Cn(t) 2 with the Catch condition n ( 0 ) =0

[0071] The solution to this differential equation is a function increasing at 0 over time, reaching equilibrium after approximately 15 ns. With a continuously irradiated modulation light or a modulation of the intensity of the irradiated modulation light, the frequency of which is significantly lower than the recombination rate, an equilibrium is established between the charge carrier generation and the recombination. The intensity in equilibrium corresponds essentially to the square root of the charge carriers induced by the recombination: ninj

[0072] For the example of a laser of the above-mentioned power, the equilibrium charge carrier density is in the range of a few 10 18 1 / cm 3 .

[0073] From the above-mentioned differential equation and the estimates regarding the irradiated modulation light and the other parameters, a charge carrier concentration in the range of 10 17 up to 10 19 Charge carriers per cm 3 This can be used to calculate a refractive index change according to the Drude Model in the range of ICh 2 i.e. , it can be estimated in the range of a few percent. Larger intensities of the modulation light increase the absorption within the material and thus the charge carrier concentration, which also increases the

[0074] In order to achieve, for example, a phase change of n between two waveguides due to a change in the refractive index, it is sufficient to provide a waveguide with a length of approximately 100 pm and a charge carrier density in the range of 10 18 up to about 10 19This results in the addition of an additional

[0075] Modulation light can be generated either by a single additional laser or by several lasers, a sufficient charge carrier concentration of free charge carriers within the material of the optical component in order to generate a required refractive index change for a phase shift of 180 °, corresponding to n.

[0076] Following this principle, various designs for optical components can be implemented in which charge carriers are formed in a part of the optical component by means of an application of high-energy light, so that the refractive index changes.

[0077] Figure 4 shows a further embodiment in which greater flexibility in adjusting the refractive index can be achieved by means of several additional laser devices for generating modulation light ML, possibly also of different wavelengths. In addition, such a design also allows a certain symmetrical shape, so that a more uniform charge carrier distribution is achieved. Figure 4 shows an optical component 3. A laser device 1 for supplying the useful light NL is connected to the signal input. In this exemplary embodiment, two laser devices 2 and 2' are provided, each of which supplies a modulation light ML and ML' to the two additional modulation inputs of the optical component 3. The waveguide structure, connected to the modulation inputs, is designed in the same way and is shown as an example in a cross-section in Figure 6.

[0078] It can be seen here again that the first waveguide structure with the waveguides 11a, 11b to 11g is arranged in one plane.

[0079] In contrast, the two waveguide structures with the branches 21a, 21b to 21g for the modulation light ML and 21a', 21b' to 21g' for the modulation light ML' are arranged above and below the first waveguide structure, respectively. In other words, the waveguides 11a, 11b to 11g are surrounded on both sides by a corresponding modulation waveguide structure. When the modulation light ML is switched on, indicated here by the arrows in Figure 6, the light is thus guided as evenly as possible onto the first waveguide structure by the coupling-out structure 22. This results in a more uniform distribution of the scattered modulation light ML in the waveguide structure with the waveguides 11a, 11b to 11g, which in turn leads to a more uniform charge carrier distribution.In addition, in this embodiment, depending on the degree of absorption, a significantly larger refractive index jump can be achieved, since the intensity can be adjusted in a larger range due to the possible higher intensity with the waveguides 21a ', 21b ' to 21g '.

[0080] A modification of this kind is shown in Figure 5. In this case, the waveguide structures for the modulation light ML and for the modulation light ML' are arranged mirror-symmetrically above and below the waveguide structure for the useful light NL. This results in the individual waveguides 21a, 21b to 21g and 21a', 21b' to 21g' being of different lengths above and below the respective waveguides 11a, 11b to 11g. This provides a degree of freedom in adjusting the interference pattern and the change in the refractive index.

[0081] Another alternative design involves providing additional mirrors or other optical or electro-optical structures above or below the waveguide structure for the useful light. These can serve to create a more uniform light distribution or a more uniform charge carrier distribution, which ultimately improves the signal quality.

[0082] Figure 7 shows an embodiment in cross section in which two additional DBR structures 31 and 31' are arranged above and below the plane of the waveguide structure for the useful light NL. The DBR structures are designed such that they increase the absorption of modulation light ML within the waveguide structure with the waveguides 11a, 11b to 11g, thereby improving the efficiency of charge carrier generation. In this context, the two planar DBR structures 31 and 31' form a vertical cavity in which the modulation light ML is ideally reflected back and forth several times until it is essentially completely absorbed by the waveguide structure for the useful light.

[0083] Figure 8 shows an alternative embodiment in which the planes of the waveguide structures for the useful light NL and the waveguide structure for the modulation light ML are arranged as close to one another as possible. In this exemplary embodiment, the distance between the waveguides 11a, 11b to 11g and the waveguides 21a, 21b to 21g for the modulation light is only a few 10 nm to a few 100 nm. As a result, the modulation light couples directly into the waveguide structure with the waveguides 11a, 11b to 11g by means of evanescent coupling and is at least partially absorbed there. This embodiment has the advantage that additional coupling structures 22 or DBR structures can basically be dispensed with, thus simplifying production. However, a DBR structure below the waveguides 11a, 11b to 11g is also possible here.

[0084] Figure 9 shows a further embodiment with an optical component that differs from the previous embodiments. As already mentioned, this is based on the fact that the fundamental principle of a refractive index change in optical components by additionally introducing modulated light is not limited to an optical phased array in the narrow sense. Rather, it is also possible, for example, to reduce the linewidth of an edge-emitting laser, to stabilize such a laser, or to flexibly adjust other optical functionalities.

[0085] In the present exemplary embodiment, the optical component 30', as in the other embodiments, also comprises a material 30 into which a waveguide 11 is embedded from a signal input to a signal output 12. The waveguide is used to supply and process the useful light NL. A resonator element 32 is connected to the waveguide via an optical coupling D, the element 32 in the present form being designed as a ring resonator. During operation of this arrangement, a single mode of the scattered useful light NL is selected, amplified, and provided at the output 12 by the optical coupling D and the geometric parameters of the ring resonator 32. In this way, an edge-emitting laser diode can be stabilized against thermal fluctuations on the one hand, and its linewidth can be significantly reduced, so that it is still a few megahertz, on the other.

[0086] Above or below this ring resonator 32 there is now provided a further partially ring-shaped waveguide element 21, at the end 33 of which a mirror or an absorbing element is arranged. An arrangement with a mirror has the advantage that non-absorbed light is reflected back into the curved waveguide 21 and can thus be absorbed again in the ring resonator. The ring-shaped structure above the ring resonator, as in the other embodiments, also has an output coupling structure with which the modulation light ML provided by the laser diode 1 is radiated into the ring resonator and generates free charge carriers there. These cause a change in the refractive index in the ring resonator, as a result of which the selected mode is shifted by the optical coupling D.By changing the intensity of the radiated modulation light, the refractive index is changed and thus a frequency modulation of the scattered useful light at the output 12 is realized.

[0087] The proposed optical component can be implemented in various ways, particularly with regard to the supply of the modulation light. Figures 10, 11 and 12 show various embodiments in this regard, with their respective cross-sections. In Figure 10, coupling into the ring resonator 32 takes place by additional mirror elements 4 which are prism-shaped. The modulation light ML is provided for this purpose by a laser device 2 which is arranged on an additional, laterally arranged support with a height of three' as the optical element. The modulation light is partly reflected in the prism-shaped mirror elements 4 and passed onto the ring resonator 32, and partly it runs further out of the first element, enters the second mirror element 4 and is reflected there.This arrangement has the advantage that it can be easily mounted on existing optical components 3 ', provided that the material forming the optical component is transparent to the modulation light.

[0088] An alternative embodiment is shown in Figure 11. In this embodiment, an additional waveguide structure 21 with a plurality of output coupling elements 22 is located above the plane of the ring resonator. These serve to output the modulation light ML in the waveguide structure 21 and direct it onto the waveguide of the ring resonator 32. Here, too, the modulation light is generated by an externally arranged second laser diode 2.

[0089] Finally, in a third embodiment, the ring resonator is arranged between two DBR structures 31. One of the DBR structures below the ring resonator is designed as a flat mirror, while the second DBR structure above the ring resonator 32 merely covers the material of the ring resonator. Here, too, an output coupling structure 22 serves to irradiate the light onto the DBR structure 31 and the material of the ring resonator.

[0090] The various implementations and designs can be combined with their individual features to generate charge carriers in an optically relevant region by absorbing modulated light, thereby changing the refractive index within this material, as explained above. This allows the realization of optical components with adjustable functionalities.

[0091] Figure 13 finally shows an embodiment of a method for operating an optically adjustable component. In this component, a signal input is provided for feeding a useful light of a first wavelength into at least one waveguide. In addition, there is a signal output at which an adjusted or adjustable useful light can be tapped. The optical component comprises a material which is transparent to the useful light and which in turn has a first band gap or is designed such that it absorbs light smaller than a predetermined wavelength. Such an optical component is now provided in step S1 and connected to a first laser device for generating the useful light.

[0092] In addition, a second laser device is provided which is designed to generate modulation light. A photon energy of the modulation light is greater than the first band gap. In the proposed method, in step S2 the useful light is radiated into the first component and processed in the desired manner in the optical component. The light processed in the component can be tapped off at the output. In a second step S2 the modulation light is now also supplied in such a way that at least part of the modulation light radiates into the material of the region relevant for the optical component. The component can be a waveguide, a resonator, a PIC or PLC or even a waveguide array, as shown in the previous exemplary embodiments.

[0093] Due to the higher photon energy, the incident modulation light is now absorbed within this range, generating free charge carriers there. Depending on the intensity of the incident modulation light, an equilibrium is established between charge carrier recombination and charge carrier generation. However, the free charge carriers simultaneously change the refractive index of the material, thereby influencing the incident useful light. The intensity of the modulation light allows this change in the refractive index to be adjusted over a predetermined range, thus altering the functionality of the optical component.

[0094] In this way, it is possible to bring about a change in the refractive index in an optical component using purely optical measures and thus influence its functionality. Depending on the application and design, these can be, for example, a phase shift, frequency modulation, optical switching or other functions. In contrast to other solutions, the change in the refractive index essentially occurs through the intensity modulation of the modulation light and can therefore reach high speeds in the range of several 100 MHz. In addition, complex additional circuitry measures are reduced; only an additional laser device is required to generate the modulation light with a higher photon energy than the useful light.

[0095] LIST OF REFERENCE SYMBOLS

[0096] 1 laser array

[0097] Laser arrangement

[0098] 3 , 3 ' phased array 3 '' phased array

[0099] 4 Mirror 11 Waveguide 11a, 11b Waveguide 11c, l ld Waveguide Ile , l lf Waveguide 11g Waveguide 12 , 12 ' Output 21 Waveguide 21a, 21b Waveguide 21c, 21d Waveguide 21e , 21f Waveguide 21g Waveguide 22 Diffractive optics 30 Material of the phased array 31 , 31 ' DBR structure 32 Ring resonator

[0100] D coupling NL useful light ML modulation light

Claims

PATENT CLAIMS Optical phase array comprising a signal input for supplying useful light of a first wavelength; a first waveguide array with at least one signal output, which is connected to the signal input and comprises a material transparent to the useful light and includes a first band gap; a first modulation input for supplying modulation light of a second wavelength; a second waveguide array connected to the first modulation input, which is arranged in the vicinity of the first waveguide array such that modulation light is conductable onto the first waveguide array, wherein the first band gap is smaller than the energy of the modulation light.Optical phase array according to claim 1, wherein the first waveguide array comprises a plurality of waveguides that lie substantially in one plane and have a defined light transit time difference from one another, and optionally, wherein the second waveguide array comprises a plurality of waveguides that lie substantially in one plane and have a defined light transit time difference from one another. Optical phase array according to claim 1, wherein the first waveguide array is configured as, or comprises, at least one of the following elements: an optical ring oscillator; a Mach-Zehnder modulator; a directional optical coupler; Optical phase array according to any of the preceding claims, wherein the first waveguide array and the second waveguide array are arranged one above the other in two substantially parallel planes. An optical phase array according to any one of the preceding claims, further comprising: a second modulation input for supplying modulation light of the second or a third wavelength; a third waveguide array connected to the second modulation input and arranged adjacent to the first waveguide array such that modulation light of the second or third wavelength is conductable onto the first waveguide array, wherein the first band gap is smaller than the energy of the light of the third wavelength. An optical phase array according to claim 5, wherein the first waveguide array is arranged between the second and the third waveguide array. An optical phase array according to claim 5 or 6, wherein the second waveguide array comprises a plurality of waveguides that lie substantially in one plane and have a defined light transit time difference from one another.An optical phase array according to any one of claims 5 to 7, wherein the second and third waveguide arrays at least partially overlap and / or are arranged in a mirror image. An optical phase array according to any one of the preceding claims, wherein the second and / or third waveguide array has an out-coupling structure, in particular in the form of a diffractive optic, which faces the first waveguide array. An optical phase array according to any one of the preceding claims, wherein the second and / or third waveguide array is spaced less than 300 nm and in particular less than 10 Øm from the first waveguide array, and in particular a space smaller than the wavelength of the modulation light and in particular a space smaller than half the wavelength of the modulation light. An optical phase array according to any of the preceding claims, wherein the propagation time differences in the waveguides of the first, second, and / or third waveguide array are formed by different lengths of the waveguides. An optical phase array according to any of the preceding claims, further comprising: a particularly planar DBR structure, which is arranged on the side of the first waveguide array opposite the second waveguide, in particular for reflecting modulation light back. An optical phase array according to any of the preceding claims, further comprising: a particularly planar distribution layer, which is arranged on the side of the first waveguide opposite the second waveguide and is configured to reflect modulation light back or to distribute charge carriers generated by modulation light in the first waveguide array.Optical phase array according to one of the preceding claims, wherein the material of the first waveguide array comprises at least one of the following components:. - InP ; - Si ; - GaAs ; - AlGaAs ; - AlGaP; and GaN; and / or the material of the second and / or third waveguide array comprises at least one of the following components: - AIN; - SiNx ; A12O3; and A resonator arrangement comprising: a waveguide connecting a signal input for supplying useful light of a first wavelength to a signal output; a resonator, in particular a ring resonator, optically coupled to the waveguide to amplify a frequency mode of the useful light in the waveguide; an arrangement placed above the resonator configured to couple modulating light of a second wavelength into the resonator; wherein the resonator comprises a bandgap material such that the resonator is substantially transparent to useful light and absorbs modulating light, forming charge carriers. A resonator arrangement according to claim 15, wherein the arrangement placed above the resonator comprises one or more deflecting mirrors; or wherein the arrangement comprises a second waveguide with diffractive optics configured to direct modulating light in the second waveguide onto the resonator.Resonator arrangement according to claim 15 or 16, further comprising: a particularly planar DBR structure, which is arranged on the side of the resonator opposite the second waveguide, in particular for back-reflecting modulation light. Laser arrangement comprising: a first laser device for generating useful light, a second laser device for generating modulation light, an optical phase array according to one of the preceding claims or a resonator arrangement according to one of the preceding claims. Method for operating an optical phase array, wherein the phase array has a signal input for supplying useful light of a first wavelength and a first waveguide array with at least. a signal output which is connected to the signal input and comprises a first band gap and is made of a material transparent to the useful light; the method comprising the steps: - Radiation of useful light into the first waveguide array; - Radiation of modulating light such that at least part of the modulating light couples into the first waveguide array; - Generating charge carriers in the first waveguide array by absorption of the coupled modulation light. A method according to claim 19, wherein the modulation light is irradiated by means of a second waveguide array arranged adjacent to the first waveguide array such that modulation light is conductable onto the first waveguide array. A method according to claim 19 or 20, wherein the first waveguide array comprises a plurality of waveguides that lie substantially in one plane and have a defined light transit time difference, and optionally, the second waveguide array comprises a plurality of waveguides that lie substantially in one plane and have a defined light transit time difference.Method according to claim 21, wherein transit time differences in the waveguides of the first, second and / or third waveguide array are formed by different lengths of the waveguides.

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