Method and System for Extracting Information from Optical Signals

Abstract

A system for providing information based on the spectral content of an optical signal includes an optical modulator for applying a time-dependent modulation to the optical signal according to at least one sub-optical modulation frequency to provide a modulated optical signal, an optoelectronic device configured to receive the modulated optical signal and responsively generate an electrical sensing signal, and a signal processing system configured to process the electrical sensing signal and generate an output correlated to at least one wavelength of the optical signal based on the modulation.

Description

Technical Field

[0001] Related Applications This application claims the benefit of priority of U.S. Provisional Patent Application No. 62 / 950,976, filed on December 20, 2019, the entire content of which is incorporated herein by reference.

Background Art

[0002] In some embodiments, the present invention relates to the analysis of optical signals, and more particularly, to a method and system for extracting information correlated with the optical wavelength or the spectrum of the optical wavelength from an optical signal.

[0003] In many applications, techniques known as measuring the optical spectrum over one or more optical wavelengths, wavelength shifts, or spectral ranges, "optical spectroscopy" or sometimes "wavelength monitoring" are required. For example, in recent years, there has been an increasing interest in the development of spectral sensing systems for healthcare services, industrial process monitoring, and environmental monitoring. Typical measurements include demonstrating the presence or absence of an analyte, determining the quality of an industrial process, sensing stress, vibration, or damage in a structure, or monitoring the reaction or binding kinetics of an analyte in a sample such as water, blood, aerosol, air, food, etc.

[0004] Optical spectroscopy is advantageous because it is highly sensitive and selective and can be used for continuous real-time monitoring without contaminating the sample. One classification of spectrometers is those that use dispersion to separate light into spectral components. Conventional dispersive spectrometers use a dispersive grating to change the momentum and angularly disperse the light, and the spectral resolution corresponds to the optical path length from the grating to the detector, and a trade-off relationship is imposed between the device size and the resolution. In recent years, the development of "compact" spectrometers has enabled many new applications due to cost reduction and portability.

[0005] U.S. Patent No. 9,714,863 discloses an optical spectrometer including a photodiode and a strain-imparting mechanism for imparting adjustable strain to the photodiode. By adjusting the strain, it is possible to adjust the bandgap of the photosensitive region of the photodiode.

[0006] Photodiode-based wavelength sensors operating based on the principle of wavelength-dependent responsivity are also known (www(dot)first-sensor(dot)com / cms / upload / datasheets / WS7(dot)56_ PCBA2_5000004(dot)pdf).

[0007] Wavelength sensors based on filters placed in front of segmented photodiode detectors are also known (www(dot)open-photonics(dot)com / Wp-content / uploads / 2015 / 09 / OPI_FeaturedTechnology_WSD_090915(dot)pdf).

Summary of the Invention

[0008] According to aspects of some embodiments of the present invention, a system for providing information based on the spectral content of an optical signal is provided. The system includes an optical modulator for applying time-dependent modulation to the optical signal according to at least one sub-optical modulation frequency to provide a modulated optical signal, an optoelectronic device configured to receive the modulated optical signal and generate an electrical sensing signal in response thereto, and a signal processing system configured to process the electrical sensing signal to generate an output correlated with at least one wavelength of the optical signal based on the modulation.

[0009] According to some embodiments of the present invention, the optoelectronic device is not biased.

[0010] According to some embodiments of the present invention, a photoelectric device responds to an electrical bias, and the system comprises an electrical drive circuit configured to apply an electrical bias signal to the photoelectric device and scan the DC level of the electrical bias signal.

[0011] According to some embodiments of the present invention, a photoelectric device responds to an electrical bias, and the system comprises an electrical drive circuit for applying an electrical bias signal modulated according to time-dependent modulation to the photoelectric device, and the signal processing system is configured to generate an output correlated with at least one wavelength based on the modulation of the electrical bias signal.

[0012] According to aspects of some embodiments of the present invention, a system for providing information based on the spectral content of an optical signal is provided. The system comprises a photoelectric device configured to respond to an electrical bias, receive an optical signal, and generate an electrical signal in response; an electrical drive circuit for applying an electrical bias signal modulated according to time-dependent modulation to the photoelectric device; and a signal processing system configured to process the electrical sensing signal and generate an output correlated with at least one wavelength of the optical signal based on the modulation of the electrical bias signal.

[0013] According to some embodiments of the present invention, the electrical bias signal is applied while maintaining a generally constant bandgap characterizing the photosensitive region of the photoelectric device.

[0014] According to some embodiments of the present invention, the electrical drive circuit is configured to scan the DC level of the electrical bias signal in addition to modulating the electrical bias signal.

[0015] According to some embodiments of the present invention, the system comprises at least one additional optoelectronic device, the modulated optical signal is also directed to the at least one additional optoelectronic device, and the signal processing system is configured to process the electrical sensing signal generated by the at least one additional optoelectronic device and generate an output based also on the electrical sensing signal generated by the at least one additional optoelectronic device.

[0016] According to some embodiments of the present invention, the signal processing system is configured to determine a variable of the sub-optical modulation frequency and generate an output based on the variable.

[0017] According to some embodiments of the present invention, the system comprises a beam splitting system for splitting the modulated optical signal into two modulated optical signals and directing the two modulated optical signals to opposite sides of the optoelectronic device.

[0018] According to some embodiments of the present invention, the system comprises an additional optoelectronic device and a beam splitting system for splitting the modulated optical signal into two modulated optical signals so as to cancel the optoelectronic wavelength dispersion between the two devices, directing one of the two modulated optical signals to the optoelectronic device, and directing the other of the two modulated optical signals to the additional optoelectronic device.

[0019] According to some embodiments of the present invention, the system comprises a reflector for reflecting the modulated optical signal to create a multiple optical path within the optoelectronic device.

[0020] According to aspects of some embodiments of the present invention, a method for providing information based on the spectral content of an optical signal is provided. The method includes applying a time-dependent modulation to the optical signal according to at least one sub-optical modulation frequency to provide a modulated optical signal, receiving the modulated optical signal by an optoelectronic device, thereby generating an electrical sensing signal in response to the modulated optical signal, and processing the electrical sensing signal to generate an output correlated with at least one wavelength of the optical signal based on the modulation.

[0021] According to some embodiments of the present invention, the optoelectronic device is unbiased.

[0022] According to some embodiments of the present invention, the optoelectronic device responds to an electrical bias, and the method includes applying an electrical bias signal to the optoelectronic device and scanning the DC level of the electrical bias signal.

[0023] According to some embodiments of the present invention, the optoelectronic device responds to an electrical bias, and the method includes applying an electrical bias signal modulated according to a time-dependent modulation to the optoelectronic device, and determining at least one wavelength is also based on the modulation of the electrical bias signal.

[0024] According to aspects of some embodiments of the present invention, a method of providing information based on the spectral content of an optical signal is provided. The method includes applying an electrical bias signal modulated according to a time-dependent modulation to an optoelectronic device responsive to an electrical bias, receiving an optical signal by the optoelectronic device during the application of the electrical bias signal, thereby generating an electrical sensing signal in response to the optical signal, and processing the electrical sensing signal to generate an output correlated with at least one wavelength of the optical signal based on the modulation of the electrical bias signal.

[0025] According to some embodiments of the present invention, the optical signal is a continuous wave (CW) signal.

[0026] According to some embodiments of the present invention, the application of the electrical bias signal is while maintaining a generally constant bandgap characterizing the photosensitive region of the optoelectronic device.

[0027] According to some embodiments of the present invention, the method includes scanning the DC level of the electrical bias signal in addition to modulating the electrical bias signal.

[0028] According to some embodiments of the present invention, the method includes receiving an optical signal by at least one additional optoelectronic device and processing an electrical sensing signal generated by the at least one additional optoelectronic device, and generating an output is also based on the electrical sensing signal generated by the at least one additional optoelectronic device.

[0029] According to some embodiments of the present invention, the method includes determining a variable of a sub-optical modulation frequency, and generating an output is also based on the variable.

[0030] According to some embodiments of the present invention, the method includes splitting a modulated optical signal into two modulated optical signals and directing the two modulated optical signals to opposite sides of an optoelectronic device.

[0031] According to some embodiments of the present invention, the method includes splitting a modulated optical signal into two modulated optical signals so as to cancel out the optoelectronic wavelength dispersion between two devices, directing one of the two modulated optical signals to an optoelectronic device, and directing the other one of the two modulated optical signals to an additional optoelectronic device.

[0032] According to some embodiments of the present invention, the method includes reflecting a modulated optical signal to create a multiple optical path within an optoelectronic device.

[0033] According to some embodiments of the present invention, the modulation includes radio frequency modulation.

[0034] According to some embodiments of the present invention, processing includes processing a modulation amplitude.

[0035] According to some embodiments of the present invention, processing includes processing a modulation phase shift.

[0036] According to some embodiments of the present invention, the optical signal is a spectral component of a multi-color beam and is spatially separated from other spectral components of the multi-color beam.

[0037] According to some embodiments of the present invention, the optical signal is multi - colored, and the system or method is applied to generate an output indicating the spectrum of the optical signal.

[0038] According to some embodiments of the present invention, the modulation is characterized by a scanned modulation frequency.

[0039] According to some embodiments of the present invention, the optical signal is monochromatic, and the system or method is applied to monitor the absolute value of the wavelength and / or the spectral shift of the wavelength.

[0040] According to some embodiments of the present invention, the optical signal indicates the strain or change in strain of a sample, and the system or method is used to determine the strain or change in strain based on at least one wavelength.

[0041] According to some embodiments of the present invention, the optical signal indicates the pressure or change in pressure applied to a sample, and the system or method is used to determine the pressure or change in pressure based on at least one wavelength.

[0042] According to some embodiments of the present invention, the optical signal indicates the temperature or change in temperature of a sample, and the system or method is used to determine the temperature or change in temperature based on at least one wavelength.

[0043] According to some embodiments of the present invention, the optical signal indicates the presence of at least one type of compound in or near a sample, and the system or method is used to determine the presence or level of at least one type of compound based on at least one wavelength.

[0044] According to some embodiments of the present invention, the optical signal indicates the accelerated motion of a sample, and the system or method is used to determine the presence or level of the accelerated motion based on at least one wavelength.

[0045] According to some embodiments of the present invention, the optoelectronic device is entrance region dominant, and the modulation frequency characterizing the modulation is greater than a value equal to 1 / √2 of the response amplitude at which the response amplitude of the optoelectronic device responds to a frequency at which the amplitude changes by no more than 10%.

[0046] According to some embodiments of the present invention, the method includes transmitting a probe signal to an optoelectronic device and receiving a response signal from the optoelectronic device, the optical signal being the response signal, and the output including at least one characteristic of the optoelectronic device.

[0047] According to some embodiments of the present invention, at least one characteristic of the optoelectronic device is selected from the group consisting of electrical characteristics, optical characteristics, material characteristics, mechanical characteristics, and time characteristics.

[0048] According to some embodiments of the present invention, at least one characteristic of the optoelectronic device is selected from the group consisting of responsivity, quantum efficiency, resistance, capacitance, electron and hole mobility, exciton mobility, doping level of the material, structure, dimensions, width of the depletion region, internal voltage level, hole diffusion coefficient and electron diffusion coefficient, drift velocity, absorption spectrum, absorption value, dielectric constant, refractive index.

[0049] According to aspects of some embodiments of the present invention, there is provided a method of receiving an optical signal modulated to carry a data stream, the optical signal being transmitted via an optical fiber and causing chromatic dispersion in the signal. The method includes receiving the modulated optical signal and, in response thereto, directing the optical signal to an optoelectronic device configured to generate an electrical sensing signal having a pulse width narrower than the pulse width of the optical signal by an amount selected to at least partially compensate for the chromatic dispersion, and processing the electrical sensing signal to generate an output indicative of the data stream.

[0050] According to aspects of some embodiments of the present invention, there is provided a method of receiving an optical signal modulated to carry a data stream, the optical signal being transmitted via an optical fiber and causing chromatic dispersion in the signal. The method comprises receiving the modulated optical signal and, in response thereto, directing the optical signal to an optoelectronic device configured to generate an electrical sensing signal having a pulse width narrower than the pulse width of the optical signal by an amount selected to at least partially compensate for the chromatic dispersion, and processing the electrical sensing signal to generate an output indicative of the data stream.

[0051] According to aspects of some embodiments of the present invention, there is provided a sensing method. The method comprises applying a time-dependent modulation to two optical signals according to at least one sub-optical modulation frequency to provide modulated optical signals, receiving the modulated optical signals by an optoelectronic device and thereby generating an electrical sensing signal in response to the modulated optical signals, wherein there is a predetermined relative phase shift between the modulated optical signals, processing the electrical sensing signal to determine the phase shift between the optical signals, and generating an output indicative of the phase shift.

[0052] According to aspects of some embodiments of the present invention, there is provided a sensing method. The method comprises splitting an optical signal into two secondary optical signals, receiving one of the secondary optical signals by an entrance side surface of an optoelectronic device and receiving another one of the secondary optical signals by a substrate side surface of the optoelectronic device, and monitoring an electrical signal generated by the optoelectronic device to identify at least one change in an environment in which the optical signal propagates.

[0053] According to aspects of some embodiments of the present invention, there is provided a sensing method. The method comprises directing an optical signal to one of an entrance side surface and a substrate side surface of an optoelectronic device, reflecting the signal back to the other one of the entrance side surface and the substrate side surface of the optoelectronic device, and monitoring an electrical signal generated by the optoelectronic device to identify at least one change in an environment in which the optical signal propagates.

[0054] According to aspects of some embodiments of the present invention, a sensing method is provided. The method includes splitting an optical signal into two secondary optical signals, receiving one of the secondary optical signals by an entrance side surface of a first optoelectronic device, receiving another one of the secondary optical signals by a substrate side surface of a second optoelectronic device, combining electrical signals generated by the first optoelectronic device and the second optoelectronic device, and monitoring the combined electrical signal to identify at least one change in an environment in which the optical signal propagates.

[0055] The system or method described above, optionally, preferably, a system or method as further detailed below, can be used for spectroscopy.

[0056] The system or method described above, optionally, preferably, a system or method as further detailed below, can be used to sense a signal transmitted via an optical fiber.

[0057] The system or method described above, optionally, preferably, a system or method as further detailed below, can be used for radio frequency - photonic signal processing.

[0058] According to aspects of some embodiments of the present invention, a method of manufacturing an optoelectronic device is provided. The method includes receiving an input optical phase shift, selecting a width of a charge carrier generation region and an absorption spectrum so as to maximize a logarithmic derivative of an intrusion parameter P with respect to the input phase shift, where the intrusion parameter P is a product of the width and the absorption spectrum, and manufacturing a pn junction according to the width and the absorption spectrum.

[0059] According to some embodiments of the present invention, the input optical phase shift is positive.

[0060] According to some embodiments of the present invention, the input optical phase shift is negative.

[0061] According to some embodiments of the present invention, the input optical phase shift is less than 0.3, or less than 0.2, or less than 0.1, or less than 0.05.

[0062] According to aspects of some embodiments of the present invention, a method for generating optoelectronic feedback is provided. The method includes generating an optical signal by a light source, directing the optical signal towards an optoelectronic device to generate an electrical signal, feeding back the electrical signal to the light source to generate a resonance signal in response to the electrical signal, and controlling the optoelectronic wavelength dispersion of the optoelectronic device to select the wavelength of the resonance signal. In some embodiments of the present invention, the resonance signal is an electrical signal generated at the output of the optoelectronic device, and in some embodiments of the present invention, the resonance signal is an optical signal generated at the output of the light source optoelectronic device.

[0063] According to some embodiments of the present invention, the optical signal is multi-color, and the optoelectronic device is selected to provide a set of electrical signals each corresponding to a different wavelength, thereby generating a set of respective optical signals.

[0064] All technical terms and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which the present invention belongs, unless otherwise defined. Methods and materials similar or equivalent to those described herein may be used in the practice or testing of embodiments of the present invention, but exemplary methods and / or materials are described below. In case of conflict, including definitions, this patent specification shall prevail. Further, the materials, methods, and examples are illustrative only and are not necessarily intended to be limiting.

[0065] Embodiments of the method and / or system of the present invention may include performing or completing a selected task manually, automatically, or a combination thereof. Further, according to the actual devices and equipment of the embodiments of the method and / or system of the present invention, some selected tasks may be implemented by hardware, software, or firmware using an operating system, or a combination thereof.

[0066] For example, the hardware for performing a selected task according to an embodiment of the present invention may be implemented as a chip or a circuit. When a selected task according to an embodiment of the present invention is implemented as software, it may be implemented as a plurality of software instructions executed by a computer using any suitable operating system. In an exemplary embodiment of the present invention, one or more tasks according to the exemplary embodiments of the method and / or system described herein are executed by a data processor such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes volatile memory for storing instructions and / or data, and / or non-volatile storage for storing instructions and / or data, such as a magnetic hard disk and / or removable media. Optionally, a network connection is also provided. A display, and / or a user input device such as a keyboard or a mouse are also optionally provided.

[0067] Some embodiments of the present invention will be described herein by way of example only with reference to the accompanying drawings. In so doing, specific reference is made in detail to the drawings, it being emphasized that the details shown are by way of example and for purposes of illustrative discussion of embodiments of the present invention. In this regard, the description, interpreted in conjunction with the drawings, will make apparent to those skilled in the art how embodiments of the present invention may be implemented.

Brief Description of the Drawings

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DETAILED DESCRIPTION OF THE INVENTION

[0069] In some embodiments, the present invention relates to the analysis of optical signals, and more particularly, to a method and system for extracting information correlated with the optical wavelength or spectrum of optical wavelengths of an optical signal from the optical signal.

[0070] Before explaining in detail at least one embodiment of the present invention, it is to be understood that the present invention is not necessarily limited to the details of construction, components, and / or arrangement of methods described in the following description, and / or shown in the drawings and / or examples. The present invention is capable of other embodiments and can be practiced or carried out in various ways.

[0071] The response of a substance that absorbs light and generates an electric current, such as, but not limited to, a semiconductor material, depends on the wavelength due to various factors such as, for example, the bandgap of the substance, the absorption spectrum of the substance, the absorption edge of the spectrum, and the quantum processes of optical absorption and mobile charge generation within the substance. The inventor has discovered that, in the processes of optical absorption, charge carrier generation, and current formation, there may be a substantial effective chromatic dispersion (ECD). Next, this effective chromatic dispersion will be described.

[0072] As used herein, a "charge carrier pair generating optical substance" refers to a substance that can absorb light and, in response to this absorption, generate, by various charge transport mechanisms such as, but not limited to, the drift or diffusion of one or more types of charge carriers, an amount of charge carrier pairs (usually electron-hole pairs) sufficient to cause a measurable net current to flow through the substance.

[0073] In this embodiment, it is contemplated that the substance is sufficiently mobile such that both types of charge carriers (e.g., both electrons and holes) contribute jointly to the net current.

[0074] In this embodiment, it is also contemplated that one type of charge carrier (e.g., electrons only) is sufficiently mobile to contribute to the net current, while the mobility of the other type of charge carrier is suppressed. One particular device well known in the art characterized by this phenomenon is known as a single-carrier detector.

[0075] FIG. 1 schematically shows a general process that occurs in a charge carrier pair generating optical substance 10 of length L when the charge carrier pair generating optical substance generates sufficiently mobile electrons and sufficiently mobile holes in response to the absorption of light. A representative example of a substance that generates both mobile electrons and mobile holes is, but not limited to, a PN photodiode. FIG. 1 represents a substance that generates both mobile electrons and mobile holes, but it should be understood that this embodiment also contemplates substances in which only one type of charge carrier contributes to the current, as will be described in more detail above.

[0076] The optical signal 12 consists of a spectrum of wavelengths in the range of λ1 ≦ λ ≦ λ2 and has an intensity P0. It enters the substance 10, for example, from its n side (cathode side). While propagating within the substance 10, the spectral components of the signal undergo absorption. The dependencies of the absorption of the minimum wavelength λ1 and the maximum wavelength λ2 of the signal 12 on the distance from the entry point of the signal 12 are depicted as curves 14 and 15, respectively. In FIG. 1, although it should not be regarded as limiting, the absorption of λ1 is stronger than that of λ2, and thus the penetration depth x1 of λ1 is shallower than the penetration depth x2 of λ2. However, x i , where i = 1, 2, is defined as the distance from the entry point of the signal 12 at which the intensity of each component of the signal 12 decreases to e-1P0. Therefore, in the region 0 ≦ x ≦ x1 of the charge carrier pair generation optical substance 10, the components of the signal with wavelength λ1 are efficiently absorbed, exciting charge carrier pairs (electron-hole pairs 16e, 16h in this embodiment). In the region 0 ≦ x ≦ x2 of the substance 10, the components of the signal with wavelength λ2 are efficiently absorbed, exciting charge carrier pairs (electron-hole pairs 18e, 18h in this embodiment). For clarity, FIG. 1 shows only the pairs 16 and 18 generated at the penetration depths x1, x2, but it should be understood that such electron-hole pairs are generated along the entire above-mentioned region. Thus, the charge carrier generation region within the substance 10 is wavelength-dependent. As a result of various charge transport mechanisms, such as diffusion and drift, one or more types of generated charge carriers move within the substance 10. In this embodiment, since both electrons and holes can move sufficiently to contribute to the current, the electrons 16e, 18e and the holes 16h, 18h move towards the opposite sides of the substance 10 (referred to as the n side and the p side in this specification, respectively). In FIG. 1, the transit times of the electrons 16e, 18e, and the holes 16h, 18h are, respectively, τ e (λ1), τ e (λ2), τ h (λ1) and τ h (λ2) as indicated. Since x2 > x1, the electron 18e propagates a longer distance than the electron 16e, and the hole 16h propagates a longer distance than the hole 18h, so τ e (λ1) < τ e (λ2) and τh (λ2) < τ h It becomes (λ1). Therefore, the transit time of the charge carriers in the substance 10 also depends on the wavelength.

[0077] The inventor has discovered that it is advantageous to apply time-dependent modulation so that the electrical signal generated by the charge carriers is reliably time-dependent. Due to the above-mentioned wavelength dependence of the charge carriers, the electrical signals generated by the charge carriers generated by different spectral components of the optical signal 10 exhibit different modulation parameters (for example, modulation phase shift, modulation amplitude, modulation frequency). The advantage of such time-dependent modulation is that the modulation parameters can be monitored to provide information about the spectral content of the optical signal 10. Specifically, one or more wavelengths of the optical signal can be calculated based on the monitored modulation parameters and, optionally, on one or more characteristics of the charge carrier pair generation optical material. Representative examples of the characteristics of the material for which the wavelength(s) of the optical signal can be calculated include, but are not limited to, the diffusion coefficient of the charge carrier(s) provided by the material, the drift velocity of the charge carriers, the structure of the material constituting the optical material, the geometric shape (for example, length) and / or material, the absorption spectrum, and the absolute value of the absorption coefficient.

[0078] Embodiments are also contemplated in which one or more wavelengths of an optical signal can be calculated based on monitored modulation parameters without having exact knowledge of the diffusion coefficient or other properties of the substance. For example, the wavelength(s) can be obtained by inputting measurement data of the monitored modulation parameter(s) into a machine learning procedure and receiving an output from the machine learning procedure that correlates to the wavelength(s). Representative examples of machine learning procedures suitable for this embodiment include, but are not limited to, clustering, correlation rule algorithms, feature evaluation algorithms, subset selection algorithms, support vector machines, classification rules, cost-sensitive classifiers, voting algorithms, stacking algorithms, Bayesian networks, decision trees, neural networks, instance-based algorithms, linear modeling algorithms, k-nearest neighbor (KNN) analysis, ensemble learning algorithms, probability models, graphical models, logistic regression (including multinomial logistic regression), gradient ascent, singular value decomposition, and principal component analysis.

[0079] Thus, the discovered effective wavelength dispersion is a process in which modulation is applied to ensure that one or more of the modulation parameters of the generated signal are also wavelength-dependent due to the wavelength dependence of the transit time of the charge carriers.

[0080] Therefore, the inventor has devised a method and system that can be used to extract information from the optical signal 12 based on its spectral content. The information to be extracted can be any type of information that depends on the spectrum. For example, the optical signal 12 may have an unknown spectral content, and the present system and method can extract and provide an output indicating its spectral content based on the wavelength dependence of the modulation parameter(s). Alternatively, the optical signal 12 may have a known spectral content, and the present system and method can extract and provide an output that correlates to its known spectral content based on the wavelength dependence of the modulation parameter(s).

[0081] Accordingly, in some exemplary embodiments of the present invention, the method and system extract and provide an output indicative of one or more optical wavelengths of the optical signal 12. In these exemplary embodiments, the spectral content of the optical signal 12 is unknown, but the modulation parameters are known. If the optical signal 12 is monochromatic, the method and system can provide, optionally and preferably, an output indicative of the central optical wavelength of the signal 12, including, optionally, the characteristic spectral width of the central wavelength. If the optical signal 12 is polychromatic, the method and system can provide, optionally and preferably, an output indicative of the optical spectrum of the signal 12, along the spectral axis, including the position of the peaks, and optionally, their associated widths as well.

[0082] In some exemplary embodiments of the present invention, the method and system serve to sense one or more non-optical but wavelength-dependent quantities. Accordingly, a system according to some embodiments of the present invention is a sensing system. In these exemplary embodiments, the spectral content of the optical signal 12 is optionally known, but the modulation parameters are optionally unknown. Alternatively, the spectral content of the optical signal 12 may be unknown, but the modulation parameters may be known. Representative examples of such wavelength-dependent quantities that can be sensed by the method and system of this embodiment include, but are not limited to, temperature, change in temperature, strain, change in strain, pressure, change in pressure, material structure (e.g., lattice structure, presence of layers), material content (e.g., presence of one or more compounds in a sample), one or more optical properties of a material, one or more electrical properties of a material, one or more time characteristics of a material, and the like.

[0083] As a representative and non-limiting example suitable for some embodiments of the present invention, consider a modulation that is temporally periodic and characterized by a modulation frequency f. In this case, consider the phase shift caused by an electrical signal as the modulation parameter. The phase shift occurring in the electrical signal generated by the j-th component of the optical signal is Ωτ i (λ j ) where λ jis the wavelength of the j-th component of the optical signal, Ω = 2πf, and i ∈ {e, h}. Monitoring this phase shift can provide information regarding the spectral components of the light. For example, by scanning a set of different modulation frequencies, a set of equations for each wavelength set can be obtained, and this set of equations can be solved to obtain the wavelength set. Preferred techniques for determining the wavelength using the monitored phase shift are provided in the Examples section below.

[0084] Also contemplated are embodiments in which the wavelength(s) is / are calculated based on the modulation amplitude of the output modulated signal, and embodiments in which the wavelength(s) is / are calculated based on both the modulation amplitude and the modulation phase shift of the modulated signal.

[0085] Also contemplated are embodiments in which the wavelength(s) is / are calculated based on the total modulation frequency response of the optical material, including frequencies that are not within the spectrum of the applied modulation frequencies.

[0086] The modulation frequency f is optionally, preferably, a sub-optical frequency.

[0087] As used herein, "optical frequency" means a frequency of from about 1 THz to about 30 PHz, and "sub-optical frequency" means any frequency of from about 0.01 kHz to about 1 THz.

[0088] In some embodiments of the present invention, the modulation frequency is within the radio frequency range, for example, from about 1 kHz to about 40 GHz. In some embodiments of the present invention, the modulation frequency is within the microwave frequency range, for example, from about 3 GHz to about 300 GHz.

[0089] The effective wavelength dispersion discovered by the inventor of the present invention and utilized in accordance with the preferred embodiments of the present invention for measuring the spectral content of an optical signal is different from the conventional wavelength dispersion because the two dispersion effects are related to different physical phenomena. Conventional wavelength dispersion is related to the wavelength dependence of the refractive index and does not require the generation of mobile charge carriers, while the discovered effective wavelength dispersion is based on optical absorption and mobile charge carrier generation. Specifically, unlike conventional wavelength dispersion, the discovered effective wavelength dispersion is based on the wavelength dependence of the transit time of charge carriers generated within a charge carrier pair generation optical material.

[0090] Modulation that ensures that the electrical signal generated by the charge carriers is time-dependent can be applied in a plurality of ways. In some embodiments of the present invention, the optical signal 12 is modulated by time-dependent modulation before entering the material 10. In some embodiments of the present invention, the bias voltage applied to the material 10 is modulated by time-dependent modulation. In some embodiments of the present invention, the optical signal 12 is modulated by time-dependent modulation before entering the material 10, but the bias voltage applied to the material 10 is not modulated by time-dependent modulation. For example, the bias voltage can be zero or a DC voltage. In some embodiments of the present invention, the bias voltage applied to the material 10 is modulated by time-dependent modulation, but the optical signal 12 is not modulated by time-dependent modulation before entering the material 10. For example, the optical signal 12 can be a continuous wave (CW) signal. In some embodiments of the present invention, the optical signal 12 is modulated by time-dependent modulation before entering the material 10, and the bias voltage applied to the material 10 is also modulated by time-dependent modulation, and this modulation may be the same as or different from the time-dependent modulation applied to the signal 12. Embodiments are also contemplated in which the optical signal 12 is modulated by time-dependent modulation before entering the material 10, but no bias is applied to the material 10.

[0091] In this embodiment, any scheme for time-dependent modulation is contemplated, including modulation that is periodic in time (e.g., sinusoidal modulation, square-wave modulation, triangular-wave modulation, sawtooth modulation, wavelet modulation, or a combination of two or more of such modulation formats), and time-dependent modulation that is not periodic in time (e.g., aperiodic modulation functions, random modulation, probabilistic modulation, etc.).

[0092] The modulation applied may include modulation of one or more of the optical intensity, optical frequency, optical phase, and polarization of the optical signal 12. When the modulation applied includes modulation of the optical frequency, one or more of the optical frequencies that make up the optical spectrum are modulated either (i) in terms of the frequency value (e.g., frequency chirp), or (ii) in terms of the intensity of the frequency component. The modulation of the intensity of the frequency component is different from the intensity modulation of the total optical intensity of the signal in that only one or more of the frequency components have their intensities modulated and at least one of the frequency components does not have its intensity modulated.

[0093] In addition to the time-dependent modulation scenarios described above, some of the embodiments of the present invention also contemplate scanning the DC level of the bias voltage applied to the charge carrier pair generating optical material. The inventor has found that such a scan can also be used to extract information regarding the spectral content of light, since the transport path of the charge carriers, e.g., carrier velocity and width of the depletion region, depends on the DC level (and AC modulation) of the bias voltage.

[0094] In any of the embodiments described herein, the time-dependent modulation of the bias to the charge carrier pair generating optical material (when used) is preferably applied without changing the spectrum-dependent characteristics of the charge carrier pair generating optical material 10 for at least 1 cycle, or at least 2 cycles, or at least 3 cycles, or at least 4 cycles, or at least 5 cycles, or at least 10 cycles, or at least 20 cycles, or at least 40 cycles of the modulation. Some examples of the above spectrum-dependent characteristics include bandgap, absorption spectrum, absorption edge, absorption value, responsivity.

[0095] As used herein, an "absorption edge" refers to a spectral region where absorption decreases rapidly with wavelength. Typically, such a rapid decrease is observed at the lower and / or upper limits of the spectral region where the substance has a substantial absorbance.

[0096] In any of the embodiments described herein, when the time-dependent modulation of the optical signal is used (if used), preferably, it is applied without changing the bandgap characterizing the charge carrier pair generation optical substance 10 for at least 1 cycle, or at least 2 cycles, or at least 3 cycles, or at least 4 cycles, or at least 5 cycles, or at least 10 cycles, or at least 20 cycles, or at least 40 cycles of the modulation.

[0097] In any of the embodiments described herein, when the time-dependent modulation of the optical signal is used (if used), optionally, preferably, it is applied without changing the absorption spectrum characterizing the charge carrier pair generation optical substance 10 for at least 1 cycle, or at least 2 cycles, or at least 3 cycles, or at least 4 cycles, or at least 5 cycles, or at least 10 cycles, or at least 20 cycles, or at least 40 cycles of the modulation.

[0098] In any of the embodiments described herein, when the time-dependent modulation of the optical signal is used (if used), optionally, preferably, it is applied without changing the absorption edge characterizing the charge carrier pair generation optical substance 10 for at least 1 cycle, or at least 2 cycles, or at least 3 cycles, or at least 4 cycles, or at least 5 cycles, or at least 10 cycles, or at least 20 cycles, or at least 40 cycles of the modulation.

[0099] In any of the embodiments described herein, when time-dependent modulation of an optical signal is used (if used), optionally, preferably, it is applied without changing the absorption value characterizing the charge carrier pair generating optical material 10 for at least 1 cycle, or at least 2 cycles, or at least 3 cycles, or at least 4 cycles, or at least 5 cycles, or at least 10 cycles, or at least 20 cycles, or at least 40 cycles of modulation.

[0100] In any of the embodiments described herein, when time-dependent modulation of an optical signal is used (if used), optionally, preferably, it is applied without changing the responsivity characterizing the charge carrier pair generating optical material 10 for at least 1 cycle, or at least 2 cycles, or at least 3 cycles, or at least 4 cycles, or at least 5 cycles, or at least 10 cycles, or at least 20 cycles, or at least 40 cycles of modulation.

[0101] As a representative and non-limiting example suitable for some embodiments of the present invention, consider a modulated optical signal having known spectral content received from the environment. The environment can include a region in space, or a sample or structure under investigation. As described above, the modulation parameter is wavelength-dependent. This modulation parameter can be monitored for each of the known components of the signal and, as described in more detail above, provides information regarding one or more quantities that are wavelength-dependent and characterize the environment.

[0102] This embodiment contemplates adjusting the bandgap of the substance 10. This adjustment can be a change in the spectral position of the bandgap and / or a change in another spectral dependence of the bandgap. In these embodiments, for each change in the bandgap, a time-dependent modulation of the intensity of the optical signal and / or the bias to the charge carrier pair generating optical substance is applied. For example, the bandgap spectral region is shifted from a first region to a second region. In this case, the time-dependent modulation is applied while maintaining the bandgap in the second region. The time-dependent modulation can also be applied multiple times. For example, in the above example of changing the bandgap from the first region to the second region, the time-dependent modulation is applied while maintaining the bandgap in the first region before the change, and then the time-dependent modulation is applied while maintaining the bandgap in the second region after the change.

[0103] The bandgap of the substance 10 can be adjusted by any method known in the art, such as by applying strain to the substance 10, or by changing its temperature, or by changing the value of the applied bias, but is not limited thereto.

[0104] This embodiment contemplates adjusting at least one property of the substance 10, and this property can optionally, preferably, be selected from the group consisting of the absorption spectrum, absorption edge, absorption value, and responsivity of the substance 10. In this case, the time-dependent modulation is applied while maintaining each property in the second region.

[0105] The technique of this embodiment can be used to provide an output indicating the spectral content of a monochromatic or polychromatic light beam.

[0106] The technique of this embodiment, when used with a monochromatic light beam, optionally preferably provides an output indicating a spectral shift of the monochromatic light beam. For example, assume that the optical signal 12 is monochromatic at wavelength λ, and assume that the modulation (of the input light or voltage bias) is sinusoidal and characterized by a modulation frequency f and a modulation function cos(Ωt) (where Ω = 2πf). The AC component of the current generated by the charge carriers can be written as I(Ω,λ)cos(Ωt+θ(Ω,λ)). Now, assume that the wavelength changes by δλ. In that case, the AC component of the output signal is [I(Ω,λ)+δI(Ω,δλ)]cos(Ωt+θ(Ω,λ)+δθ(Ω,δλ)). Here, δθ(Ω,δλ) is the change in the phase shift due to the change δλ in the wavelength of the light, and δI(Ω,δλ) is the change in the modulation amplitude due to the change δλ in the wavelength of the light. The change δλ in the wavelength can be detected by monitoring the phase shift θ(Ω,λ)+δθ(Ω,δλ) and optionally preferably also monitoring the amplitude [I(Ω,λ)+δI(Ω,δλ)]. The inventor has found that such monitoring can achieve a spectral resolution of less than 1 nm, more preferably less than 1 pm, and even more preferably less than 1 fm.

[0107] The technique of this embodiment, when used with a multi-color light beam, optionally, preferably, provides an output indicating that it is the spectrum of the beam. For example, assuming that the optical signal 12 has an optical spectrum S(λ), and assuming that the modulation (of the input light or voltage bias) is sinusoidal and characterized by a modulation frequency f and a modulation function cos(Ωt) (where Ω = 2πf). The AC component of the current generated by the charge carriers can be written as I(Ω,S(λ))cos(Ωt+θ((Ω,S(λ))). Here, θ((Ω,S(λ)) is the generated phase shift. The modulation frequency f is scanned, and for each frequency, the output amplitude I(Ω,S(λ)) and / or the phase shift θ((Ω,S(λ)) are recorded. This generates a set of equations from which the spectral content of the beam can be determined based on the characteristic wavelength dispersion of the substance 10. For example, assuming that the optical signal 12 has a spectral bandwidth Δλ, and assuming that it is desirable to determine S(λ) with a spectral resolution of Δλ / m, by repeating the modulation for m different modulation frequencies, more than m equations are constructed, and for each of the m spectral points to be decomposed within Δλ, the amplitude S(λ i ), i = 1,2,···,m is determined.

[0108] The technique of this embodiment can also be used to improve the spectral resolution of another spectrometer. For example, the technique of this embodiment can be applied to the spectral components of a multi-color beam separated from other spectral components of the beam, for example, spatially, temporally, or by other techniques, and the technique of this embodiment can provide an output indicating the spectrum of the separated components. As a representative example, a spectrometer that spatially separates an input optical beam into n spectral components (for example, using a diffraction grating) is considered, and each of these n components is characterized by a wavelength band of Δλ. By applying the technique of this embodiment to each of these components and outputting the spectra of m sub-bands each having a spectral width of approximately Δλ / m, a spectral resolution m times better than the spectral resolution obtained by spatial separation can be achieved.

[0109] Before providing a more detailed description of the method and system for measuring the optical wavelength or the spectrum of the optical wavelength, as depicted above and according to the preferred embodiments of the present invention, attention is directed to the advantages and potential uses provided thereby.

[0110] A particular advantage of the technique of this embodiment is that it can provide high spectral resolution, ranging from nanometers to sub-nanometer resolution, while being based on inexpensive components.

[0111] Spectrometers and wavelength sensors are widely used in various applications but rely on conventional means. For example, angular dispersion can be utilized by spatially separating the components of light using, for example, a diffraction grating or an optical fiber. In another technique, an interferometric method such as a Fabry - Perot interferometer or a Michelson interferometer is used to extract spectral information. The available high - performance multi - grating macroscopic spectrometers feature a spectral resolution R = λ / Δλ that can potentially exceed R = 10 6 where Δλ represents the 3dB power bandwidth at a specific wavelength setting. However, these are bulky, expensive, and may have moving mechanical parts. More compact systems, such as micro - spectrometers fabricated using silicon - process - compatible technology, have a spectral resolution that is 3 - 4 orders of magnitude lower than that of the above - mentioned high - performance multi - grating macroscopic spectrometers.

[0112] In experiments conducted by the present inventors, it has been found that by utilizing the discovered effective wavelength dispersion based on the wavelength dependence of the transit time of charge carriers, the size and cost of the system can be significantly reduced without sacrificing spectral resolution. For example, the present inventors have experimentally demonstrated that a germanium PN photodiode, which can have a net optical propagation length much shorter than 1 mm, can provide an effective wavelength dispersion equivalent to that induced by conventional refraction accumulated over 210 km of a conventional SMF28 optical fiber.

[0113] Next, refer to FIGS. 2A and 2B, which are schematic diagrams of a system 20 for providing an output correlated with the spectral content of an optical signal, according to some embodiments of the present invention. Referring to FIG. 2A, system 20 optionally, preferably, comprises an optical modulator 22 configured to apply a time-dependent modulation to optical signal 12. This modulation is optionally, preferably, external modulation, where the unmodulated optical signal 12 is received from a sample or an external source (not shown) and is modulated by a modulator 22 that receives a modulation signal from a controller 28. The controller 28 can include dedicated circuitry for generating the modulation signal. Embodiments where the modulation is direct modulation are also preferred, in which case the optical modulator 22 also functions as a light source that receives a modulation signal from the controller 28 and generates a modulated signal 24. The time-dependent modulation applied by the modulator 22 is optionally, preferably, characterized by at least one sub-optical modulation frequency f.

[0114] System 20 also comprises one or more optoelectronic devices 34, each configured to receive the modulated optical signal 24 and in response generate an electrical sensing signal 36. In FIGS. 2A and 2B, only one optoelectronic device 34 is shown for system 20, but in some embodiments of the present invention, it should be understood that system 20 can comprise a plurality of optoelectronic devices 34 arranged in an optical configuration that can be in series, or in parallel, or a combination of series and parallel. In a parallel optical configuration, the light is split into M parallel paths and illuminates M systems 20 simultaneously. In a series optical configuration, the light illuminates the detector of one system 20, and a portion of the light exits this first system 20 and illuminates one of another system 20, and so on.

[0115] Each of the optoelectronic device(s) 34 typically includes a photosensitive region 38, which preferably is at least partially made of a charge carrier pair generating optical material such as the material 10, but is not limited thereto. In some embodiments of the present invention, two or more of the devices 34 have photosensitive regions characterized by different responses to light. For example, two or more of the devices 34 may have different bandgap spectral positions, or different wavelength dependencies of the phase shift as a function of modulation frequency, or other such things. If there are multiple devices 34, they may be applied by the same bias voltage or voltage modulation, or two or more of the devices 34 may be applied with different bias voltages or voltage modulation.

[0116] Examples of materials that can function as the charge carrier pair generating optical substance 10 and that may be included in the photosensitive region 38 include, but are not limited to, semiconductors, organic materials, perovskites, polymers, plastics, dielectric materials, metallic materials, inorganic materials, p-type materials, n-type materials, intrinsic materials, undoped materials, doped materials, PN junctions, PIN junctions, nanowires, plasmonic materials, and the like. For example, the optoelectronic device 34 can include at least one of a PN photodiode, a PIN photodiode, a single-pass carrier photodiode, a metal-semiconductor-metal detector, a Schottky photodiode, a photoconductor, a photovoltaic sensor, a phototransistor, a photore resistor, a photomultiplier tube, an avalanche photodiode, a photodetector, a photoemissive detector, a CCD detector, a CMOS detector, a Golay cell, a bolometer, a thermal detector, a single-photon detector. Further, each of the above detectors is based on a specific physical mechanism for current generation induced by light absorption. The optoelectronic device 34 can include one or more of these physical mechanisms. The optoelectronic device 34 may optionally include additional components such as an internal circuit board 40 for pre-amplification, signal routing, etc., as is well known in the art. The optoelectronic device can have various sizes. Conventional photodiodes have an optical propagation length in the range of 100 nm, 1 micron, 10 microns, 100 microns, 1 mm, or more in the photoabsorption region, and their width or diameter is also nominally in the same range. Other types of optoelectronic devices, such as wires that generate charge carrier pairs, can have a lateral diameter in the range of 1 nm, 10 nm, 100 nm, 1 micron, 10 microns or more, and the optical propagation length ranges from nanometers to meters. Many other types of geometries, materials, and physical mechanisms are also contemplated.

[0117] In the embodiment shown in FIG. 2B, the optoelectronic device(s) 34 responds to an electrical bias and receives the optical signal 12. In this embodiment, the controller 28 functions as an electrical drive circuit for applying an electrical bias signal that is modulated according to a time-dependent modulation to one or more of the optoelectronic device(s) 34, and this modulation is optionally, preferably, characterized by at least one sub-optical modulation frequency f. Optionally, the controller 28 scans the DC level of the applied electrical bias signal.

[0118] In some embodiments of the present invention, the material that the photosensitive region 38 may include is selected according to the expected wavelength of the optical signal used by the system 20. Preferably, this material is selected according to its wavelength-dependent absorption spectrum α. As demonstrated in the Examples section below, the quantity (1 / α)dα / dλ is the differential coefficient of the logarithm of the absorption spectrum with respect to wavelength, is proportional to the sensitivity of the device 34 to optoelectronic wavelength dispersion, and shows a peak when plotted as a function of wavelength, and the position of the peak is different for different materials. Therefore, according to some embodiments of the present invention, the material that the photosensitive region 38 may include is selected such that the quantity (1 / α)dα / dλ reaches a peak within the expected wavelength range of the optical signal. Alternatively, for a given device 34 in which the photosensitive region 38 is made of a material having an absorption spectrum α, it is also possible to select the wavelength of the optical signal directed to the device 34 within the range where the quantity (1 / α)dα / dλ reaches a peak.

[0119] In some embodiments of the present invention, the size of the photosensitive region 38 is also selected according to the expected wavelength of the optical signal used by the system 20. The inventors have found that the sensitivity of the device 34 to optoelectronic wavelength dispersion is also proportional to the quantity Pdθ / dP, which is the differential coefficient of the phase shift θ with respect to the logarithm of P. However, P is a dimensionless parameter defined as αW, where W is either the optical inlet region, or the opposing region (also called the substrate region), or the sum region of both regions (see, for example, FIG. 8, W is W E or W S either or W E +WS It is the width of the active charge pair generation region (which can be).

[0120] The P parameter can be regarded as a parameter representing the ratio between the dimension of the device 34 and the penetration depth of the illumination light, and this will depend on the wavelength of the light. In some embodiments of the present invention, the width of the side surface of the device 34 that receives the optical signal is selected to optimize the value of the P parameter. In other embodiments, the width on the substrate side is selected to optimize the P parameter. In yet additional embodiments, the sum of the P parameters of the two regions is optimized. In the experiments conducted by the inventors, it has been found that an appropriate sensitivity has been achieved for a value of P of about 3. Therefore, the width of the side surface of the device 34 that receives the optical signal is optionally, preferably, about 3 times (for example, about 2.5 times to about 3.5 times) larger than the light penetration depth of the light for which the device is designed to receive.

[0121] The optoelectronic device(s) 34 typically have a first side 35 and a second side 37. The side through which light enters the device 34 (side 35 in FIGS. 2A and 2B) is called the entrance side. The side opposite the entrance side is called the substrate side. Thus, for example, in FIG. 2A, side 35 is the entrance side and side 37 is the substrate side. The widths of the charge pair generation regions of the device 34 may be different. When light enters the device 34 such that the width of the charge pair generation region at the entrance side is much larger (e.g., at least 4 times, or 8 times, or 16 times, or 32 times, or 64 times, or 128 times larger) than the width of the charge pair generation region at the substrate side, the device 34 is called an "entrance region dominant". Conversely, when light enters the device 34 such that the width of the charge pair generation region at the substrate side is much larger (e.g., at least 4 times, or 8 times, or 16 times, or 32 times, or 64 times, or 128 times larger) than the width of the charge pair generation region at the entrance side, the device 34 is called a "substrate region dominant". When light enters the device 34 such that the width of the charge pair generation region at the entrance side is approximately the same as the width of the charge pair generation region at the substrate side, the device 34 is called a "dual region device". The parameter q = W E / (W E +W S) It is convenient to define that when q approaches 1 (for example, q≥0.8, or q≥0.9, or q≥0.99, or q≥0.999), the device becomes "entrance region dominant", and when q approaches 0 (for example, q≤0.2, or q≤0.1, or q≤0.01, or q≤0.1), the device becomes "substrate region dominant", and when q is sufficiently far from 0 and 1 (for example, 0.001 < q < 0.999, or 0.01 < q < 0.99, or 0.1 < q < 0.9, or 0.2 < q < 0.8), the device 34 is called a "dual region device". When the device 34 is entrance region dominant, in some embodiments of the present invention, the modulation frequency f can exceed a value fc at which the response amplitude of the optoelectronic device is equal to 1 / √2 of its response amplitude in a frequency region of a sufficiently low frequency. However, the frequency region of a sufficiently low frequency is a region where the response amplitude does not change by more than 10%, or does not change by more than 5%, or does not change by more than 1% over that region due to the modulation frequency. The inventors have found that in an entrance region dominant device, the sensitivity of the device 34 to optoelectronic wavelength dispersion increases with frequency in a region where the frequency exceeds fc. In any of the above embodiments, the electrical sensing signal 36 generated by each of the devices 34 is preferably transmitted to a signal processing system 42 configured to process the signal(s) 36 to determine a measure correlated with at least one wavelength of the optical signal based on the modulation. The signal processing applied by the signal processing system 42 can be in the time domain, the frequency domain, or both the time domain and the frequency domain using any known type of signal processing technique.

[0122] The signal processing system 42 optionally and preferably generates an output indicating the determined wavelength. For example, the processing system 42 can generate a graphical display 44 of the spectrum of the signal 12 on the display device 46. Alternatively or additionally, the processing system 42 can generate an output representing a change at one or more of the determined wavelength(s). Alternatively or additionally, the processing system 42 can generate an output representing one or more wavelength-dependent quantities other than one or more wavelengths of the signal 12, as will be described in more detail above.

[0123] In some embodiments of the present invention, the signal processing 42 determines a variable of the modulation frequency spectrum when comparing the input modulation spectrum with the output modulation spectrum. For example, the processing 42 can determine the spectrum of the modulation. The advantage of these embodiments is that new modulation frequencies can arise as a result of the optoelectronic interaction of light with the optically active material generating electron-hole pairs, or for example, some of the applied modulation frequencies are enhanced and others are suppressed. By monitoring the variable of the modulation frequency, it is possible to increase the amount of information provided by the system 20. Such information, once analyzed, can improve the accuracy of the system 20. By way of example, and not to be considered limiting, the frequency spectrum of the modulation can be input into the machine learning procedure described above to increase the feature space and enhance the likelihood of a more accurate output.

[0124] In some embodiments of the present invention, a controller 28 that controls the modulation (of the signal 12 and / or the bias voltage) and a signal processing system 42 that processes the electrical sensing signal 36 are provided as a unified system configured to perform both the supply of the modulation signal to the modulator 22 and the processing of the sensing signal. These embodiments are advantageous because they allow the processing to be synchronized with the modulation. Alternatively, the controller 28 and the processing system 42 may communicate with each other for synchronization.

[0125] To clarify the instructions, FIG. 2A shows system 20 in an embodiment where controller 28 controls only modulator 22 (such that only the optical signal is modulated), and FIG. 2B shows system 20 in an embodiment where controller 28 controls only the voltage bias of device 34 (such that only the bias is modulated). However, embodiments will be understood where controller 28 is configured to control both modulator 22 and the voltage bias applied to device 34. Those of ordinary skill in the art provided with the details described herein should understand how to adapt FIGS. 2A and / or 2B for such embodiments.

[0126] When controller 28 is enabled to control both modulator 22 and the bias of device 34, controller 28 can modulate both optical signal 12 and the voltage bias applied to device 34 by time-dependent modulation. In these embodiments, signal processing system 42 determines a measure correlated to the wavelength(s) based on both modulations. For example, the modulation frequency can be scanned to obtain a set of equations for each set of wavelengths, where one or more of this set of equations can be obtained based on (i) the modulation frequency of the optical signal, (ii) the modulation frequency of the bias, or (iii) the modulation frequency of the optical signal and the modulation frequency of the bias. Then, the obtained set of equations can be solved to obtain a set of wavelengths.

[0127] Controller 28 can also be used to scan the DC level of the bias to device 34 as described above. When controller 28 is enabled to control both modulator 22 and the bias of device 34, controller 28 can modulate optical signal 12 and scan the DC level of the bias by time-dependent modulation. The DC level of the bias can be scanned with or without modulation of the bias as desired.

[0128] Figures 2C and 2D are schematic diagrams of system 20 in an embodiment where light is split before entering device 34. In these embodiments, system 20 includes a beam splitting system 60 for splitting signal 24 (FIG. 2C) or 12 (FIG. 2D) into two optical signals 13 and directing the two optical signals 13 towards opposing sides 35 and 37 of device 34.

[0129] Figures 2E and 2F are schematic diagrams of system 20 in an embodiment where there are two devices 34a and 34b, with one device being dominant in the entrance region and the other device being dominant in the substrate region. Beam splitting system 60 splits signal 24 (FIG. 2E) or 12 (FIG. 2F) into two optical signals 13, directs one of the two signals 13 towards the first side 35 of device 34a, and directs the other of the two signals 13 towards the first side 35 of device 34b. Signal processing system 42 receives electrical signals 36 from both devices 34a and 34b, combines them, and generates an output as further detailed above.

[0130] Figures 2G and 2H are schematic diagrams of system 20 in an embodiment where system 20 employs a reflector 62 to reflect optical signal 24 (FIG. 2G) or 12 (FIG. 2F) to create a multiple optical path within device 24.

[0131] The configurations shown in FIGS. 2C - 2H are particularly useful when it is desired to cancel out optoelectronic wavelength dispersion. As demonstrated in the Examples section below, the inventors have discovered that the optoelectronic wavelength dispersion of device 34 can have opposite signs for an entrance region - dominant device and a substrate region - dominant device. Based on this discovery, the inventors have devised the configurations shown in FIGS. 2C - 2H because when an optical signal enters the same device 34 from two opposing sides, or when it enters two devices where one is dominant in the entrance region and the other is dominant in the substrate region, the optoelectronic wavelength dispersion indicated by one signal cancels out the optoelectronic wavelength dispersion indicated by the other signal.

[0132] Also, a dual-region device is fabricated such that the optoelectronic wavelength dispersion is suppressed for a specific wavelength of signal 12 (e.g., -1 to 1, or -0.5 to 0.5, or -0.1 to 0.1 deg / nm, or less), or fabricated parameters (e.g., width W E and W S , coefficient α, etc.) are selected. Embodiments are also contemplated.

[0133] The cancellation or suppression of optoelectronic wavelength dispersion can be utilized, for example, in applications where device 34 is used as a sensor for environmental quantities such as temperature, pressure, strain, vibration, and the like, but not limited thereto. This is because the cancellation of optoelectronic wavelength dispersion makes device 34 more sensitive to changes in the wavelength of the signal. Therefore, a configuration in which optoelectronic wavelength dispersion is canceled can be used in a sensing method in which a change in an environmental quantity that affects the wavelength of light causes a change in the electrical signal generated by the device. Furthermore, zero OED is useful when it is desired to detect pulsed light in such a way that the output pulse of the detector is not broadened due to OED.

[0134] The optical signal is received by both the first and second sides of the same or different optoelectronic devices, and the signal(s) generated by the device(s) is / are monitored to identify changes in the signal(s). Since the change in the signal correlates with the change in the wavelength of the signal, monitoring makes it possible to identify changes in the environment near the device.

[0135] The inventors also contemplate embodiments in which the two signals enter from the same side of device 34. In these embodiments, it is possible to select a predetermined relative modulation phase shift between the two optical signals, for example, a relative modulation phase shift of about 0.4π to about 0.6π, or about 0.9π to about 1.1π. For example, when the relative modulation phase shift is about 0.9π to about 1.1π, the AC component of one signal cancels the AC component of the other signal. The signals are optionally, preferably, of different wavelengths, but the same modulation frequency is used for both signals. The modulation frequency can be selected such that, for the particular wavelengths of the two signals, the AC electrical signal generated by device 34 is zero or nearly zero (e.g., less than 10%, or less than 5%, or less than 1% of the amplitude of the electrical signal that would have been generated if the two signals had the same wavelength). In the experiments conducted by the inventors, it was found that cancellation of the electrical signal can be achieved by selecting these wavelengths such that the respective absorption coefficients of device 34 with respect to the wavelengths differ by about 10 times. For example, one particular set of input wavelengths for a Ge photodiode is the wavelength pair 1520 nm and 1580 nm, but many other combinations of wavelengths can be used.

[0136] The inventors have found that such cancellation makes the electrical signal generated by device 34 sensitive to the phase shift between the two signals, and a small change in the phase shift results in a large change in the electrical signal. Thus, in these embodiments, the electrical sensing signal generated by device 34 is analyzed to determine the phase shift between the optical signals, and processor 42 optionally, preferably, generates an output indicative of the phase shift. These embodiments are useful in any system in which measurement of the phase shift of the signal and / or measurement of the phase shift of the signal is desired. Representative examples of systems suitable for this embodiment include systems for measuring the internal structure of an object, systems for measuring the distance to an object, systems for measuring the motion characteristics of an object, interferometer systems, systems for measuring the flow of a fluid (gas or liquid), high-frequency transceiver systems, optical transceiver systems, communication systems, signal generation systems, etc., but are not limited thereto.

[0137] As an example, embodiments in which a phase shift is monitored can be used in a sensing system that measures one or more properties of an object. In these embodiments, a modulated signal interacts with the object. After the interaction, a change in the modulation of the signal is analyzed to extract one or more properties of the object. Here, the properties can be related to the structure of the object, the position of the object, the movement of the object, or the thermal state of the object. Transmitting the modulated signal to the object can include generating a predetermined phase shift between the transmitted modulated signal and a reference signal. The analysis can include detecting a phase shift between the signal received from the object and the reference signal.

[0138] Next, refer to FIG. 3, which is a flowchart diagram of a method suitable for measuring the spectral content of an optical signal according to various exemplary embodiments of the present invention. It should be understood that, unless otherwise defined, the operations described below can be performed simultaneously or sequentially in many combinations or execution orders. That is, the order of the flowchart diagram should not be regarded as limiting. For example, two or more operations that appear in a specific order in the following description or flowchart diagram can be performed in a different order (e.g., reverse order) or substantially simultaneously. Further, some of the operations described below are optional operations and may not be performed.

[0139] The method starts at 50 and optionally, preferably, proceeds to 51 as further detailed above, where a time-dependent modulation is applied to the optical signal. Alternatively, or if desired, additionally, the method proceeds to 52 as further detailed above, where an optoelectronic device, e.g., device 34, may be applied with an electrical bias signal modulated according to the time-dependent modulation.

[0140] In some embodiments of the present invention, the method proceeds to 53 where the DC level of the electrical bias signal is scanned. Operation 53 can be performed in combination with either of operations 51 and 52. In some optional embodiments of the present invention, the method proceeds to 54 where the bandgap characterizing the photosensitive region of the optoelectronic device (e.g., photosensitive region 38) is adjusted to match the expected spectrum of the optical signal. Operation 54 is preferably performed intermittently, preferably with operation 52 (if employed) and optionally with operation 51 (if employed), so as to maintain the bandgap, absorption spectrum, absorption edge, absorption value, and / or responsivity at a generally constant value while at least 1 cycle, or at least 2 cycles, or at least 3 cycles, or at least 4 cycles, or at least 5 cycles, or at least 10 cycles, or at least 20 cycles, or at least 40 cycles of modulation are completed, as described in further detail above.

[0141] The method proceeds to 55 where the optical signal is received by the optoelectronic device, thereby generating an electrical sensing signal in response to the optical signal. In embodiments where operation 51 is performed, the optoelectronic device is caused to receive the modulated optical signal. In embodiments where operation 51 is not performed, the optoelectronic device is caused to receive the unmodulated optical signal.

[0142] The method can loop back from 55 to 51 and / or 52 so as to scan the modulation frequency, thereby providing a set of electrical sensing signals where each signal corresponds to a different modulation frequency. The method proceeds to 56 where, as described in further detail above, the electrical sensing signal is processed to determine a measure correlating to one or more wavelengths (plural) of the optical signal based on the modulation. The method proceeds to 57 where an output correlated to the wavelength(s) (plural) is generated and ends at 58.

[0143] The techniques of this embodiment can be used to determine the strain or change in strain of a sample or structure. Representative examples of such applications include the measurement of the strain of a transparent isotropic material that becomes anisotropic when twisted, bent, or stretched. To determine the strain or change in strain, an optical beam is interacted with the sample to provide an optical signal indicative of the strain or change in strain of the sample, and by the techniques of this embodiment, an output including the value of the strain or change in strain is generated. Since strain is generally a result of the applied stress, these embodiments can also be used to measure the stress or pressure applied to the sample, or the change in the stress or pressure applied to the sample.

[0144] The techniques of this embodiment can be used to measure environmental quantities such as, but not limited to, temperature. Representative examples of such applications include spectroscopically measuring the temperature of a medium by analyzing the Raman spectrum or blackbody radiation spectrum of the medium. Another example of such an application includes measuring infrared radiation scattered by a medium such as, but not limited to, tissue. Additional examples of such applications include band-edge temperature measurements where transmission spectroscopy, specular reflection spectroscopy, or diffuse reflection spectroscopy is used to collect light from a sample such as, but not limited to, a semiconductor substrate, determine the spectrum of the collected light, and extract the temperature from the spectrum. To determine what the temperature is or the change in temperature, the optical beam is interacted with the sample to provide an optical signal indicative of what the temperature is or the change in temperature, and by the techniques of this embodiment, an output including the value of the temperature or change in temperature is generated.

[0145] The technique of this embodiment can be used to determine the presence of at least one type of compound in or near a sample. Representative examples of such applications include chemical analysis by spectroscopy. In such applications, the presence of a compound in a sample is determined based on the spectral lines of light transmitted through or reflected from the sample (each compound has characteristic spectral lines). To determine the presence of a compound in or near a sample, a light beam is made to interact with the sample to provide an optical signal indicating the presence of the compound, and by the technique of this embodiment, one or more spectral lines in the optical signal are determined, and an output representing the presence, absence, or level of the compound(s) in the sample is generated based on the determined spectral lines.

[0146] The technique of this embodiment can be used to determine the molecular composition of a sample. Representative examples of such applications include vibrational spectroscopy in which light, generally infrared light, is used to excite molecular vibrations in a sample, resulting in absorption at its resonant frequency. By determining the spectrum of the light after excitation, it becomes possible to examine the fundamental vibrations and the associated rotational-vibrational structure.

[0147] To determine the accelerated motion of a sample, a light beam is made to interact with the sample to provide an optical signal indicating that it is accelerated motion. The technique of this embodiment determines the spectrum of the optical signal and generates an output representing the presence or level of the accelerated motion based on the determined spectrum.

[0148] When the technique of this embodiment is used in spectroscopic measurement (such as spectroscopic measurement of temperature, spectrochemical analysis, vibrational spectroscopy, etc.), it is particularly advantageous to use a system including two or more optoelectronic devices 34, as such a configuration may increase the measurement accuracy. In these embodiments, each of the devices 34 can have a different response to light so that the system can use more data to more accurately determine the spectral content of the light.

[0149] The use of a system including two or more optoelectronic devices 34 is also advantageous when the techniques of this embodiment are used to sense an environmental quantity (e.g., temperature) or a structural quantity (e.g., structural strain). In such a configuration, the optoelectronic devices 34 can be distributed in the environment or on the structure at several locations, enabling the environmental quantity or the structural quantity to be sensed simultaneously at multiple locations.

[0150] The techniques of this embodiment can be used in optical communication, particularly to at least partially compensate for the wavelength dispersion of a modulated optical signal transmitted via an optical fiber.

[0151] Dispersion is a known limitation in optical communication systems because it is the main reason for the broadening of pulses in an optical fiber. In particular, in an optical fiber system, dispersion becomes a problem at high bit rates (e.g., exceeding 10 Gb / s). For example, an SMF-28 fiber has DL = 17 P S / nm per kilometer. Thus, a 50-kilometer SMF-28 fiber has a DL of approximately 850 P S / nm. To counteract this effect, it is desirable to compensate for this dispersion by introducing a dispersion compensation device having a DL of -850 P S / nm.

[0152] Conventional dispersion compensation techniques include chirped fiber Bragg gratings and dispersion compensation fibers. In a fiber Bragg grating system, the dispersed light is directed towards the fiber Bragg grating. Since the group velocity of shorter wavelengths is faster, they precede other wavelengths, and longer wavelengths lag behind. The pitch of the Bragg grating and the chirp of the pitch are selected such that the short-wavelength side lags behind the long-wavelength side by just the right amount to compensate for the dispersion. A dispersion compensation fiber system includes a fiber spool with an inverse dispersion profile to cancel out the effect of dispersion over a specific length (usually a length of several tens of kilometers or less) of the fiber.

[0153] The inventor has found that the effective wavelength dispersion discovered can be used for dispersion compensation without the need to introduce bulky and expensive components such as chirped fiber Bragg gratings and / or dispersion compensating fibers.

[0154] Accordingly, in various exemplary embodiments of the present invention, an optical signal modulated to carry a data stream exits an optical fiber and is directed to an optoelectronic device such as, but not limited to, device 34. Device 34 receives the modulated optical signal and generates an electrical sensing signal in response thereto. The effective wavelength dispersion of the optoelectronic device is preferably selected such that the pulse width of the generated electrical sensing signal is narrower by an amount that at least partially compensates for the wavelength dispersion than the pulse width of the optical signal exiting the optical fiber. Thereafter, as is known in the art of optical communications, the electrical signal can be processed to generate an output indicative of the modulation of the optical signal and thus the modulation of the data stream.

[0155] The techniques of this embodiment can be used to examine the characteristics of fabricated structures and devices, particularly optoelectronic devices, although this is not necessarily the case. In these embodiments, a probe signal can be transmitted to the structure or device under investigation, and a response signal can be received from the structure or device under investigation. This response signal can be designated as signal 12 and analyzed, as described in further detail above, to provide an output indicative of one or more characteristics of the structure or device under investigation. For example, a probe signal can be transmitted to an optoelectronic device and the response signal analyzed to determine one or more characteristics (e.g., electrical, optical, and / or temporal characteristics). Representative examples of characteristics that can be determined and output in accordance with some embodiments of the present invention include, but are not limited to, responsivity, quantum efficiency, resistance, capacitance, electron and hole mobility, doping level, structure, dimensions, width of depletion region, internal voltage level, hole and electron diffusion coefficients, drift velocity, absorption spectrum, absorption value, other electrical characteristics, other optical characteristics, and the like.

[0156] As used herein, the term "about" means ±10%. As used herein, the word "exemplary" is used in the sense of "serving as an example, instance, or illustration". Any embodiment described as "exemplary" should not necessarily be construed as preferred or advantageous over other embodiments, and / or does not exclude the incorporation of features from other embodiments.

[0157] As used herein, the phrase "optionally" is used to mean "provided in some embodiments and not provided in other embodiments". Any particular embodiment of the invention can include a plurality of "optional" features as long as such features are not inconsistent.

[0158] The terms "comprises", "comprising", "includes", "including", "having" and their cognates mean "including but not limited to".

[0159] The term "consisting of" means "including and limited to".

[0160] The term "consisting essentially of" means that a composition, method or structure can include additional ingredients, steps and / or parts, but only if the additional ingredients, steps and / or parts do not substantially change the basic and novel characteristics of the claimed composition, method or structure.

[0161] As used herein, the singular forms "a", "an" and "the" include the plural referents unless the context clearly dictates otherwise. For example, the term "compound" or "at least one compound" can include a plurality of compounds including mixtures thereof.

[0162] Throughout this application, various embodiments of the invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Thus, the description of a range should be considered to specifically disclose not only the individual numerical values within that range but also all possible sub-ranges. For example, a description of a range such as 1 to 6 should be considered to specifically disclose sub-ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., as well as the individual numerical values within that range, e.g., 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0163] When a numerical range is indicated herein, it always means that the range includes any cited number (fractional or integer) within the indicated range. Herein, the expressions "varying between" a first reference number and a second reference number, and "varying from" a first reference number "to" a second reference number are used interchangeably, and these expressions are intended to include the first and second reference numbers and all fractional and integer numerical values therebetween.

[0164] It is understood that certain features of the invention, which are described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, for the sake of brevity, the various features of the invention that are described in the context of a single embodiment may also be provided separately, or in any suitable partial combination, or as suitable in any other described embodiment of the invention. Specific features described in the context of various embodiments should not be considered essential features of those embodiments, except where the embodiments would not function without those elements.

[0165] The various embodiments and aspects of the invention described above and recited in the following claims can find experimental support in the following examples.

[0166] [Examples] Next, with the above description, refer to the following examples that non - limitatively show some embodiments of the present invention.

[0167] Example 1 Improvement of the spectral resolution of a spectrometer FIG. 4 is a schematic diagram of a spectrometer that uses both spatial separation and effective wavelength dispersion according to some embodiments of the present invention.

[0168] A polychromatic light beam from a light source is directed to a grating by, for example, one or more mirrors to spatially separate the spectral components of the light. For example, the grating can provide n spatially separated components (5 components are shown in FIG. 4), each characterized by a wavelength band of Δλ. Next, each of the components is directed to a system such as system 20 and subjected to the processing as described above. Each of the systems scans the modulation frequency through m predetermined modulation frequencies, and as a result, can output spectra of m sub - bands for each spatially resolved component. For example, each sub - band has a spectral width of about Δλ / m, and as a result, can provide a spectral resolution that is m times better than the spectral resolution provided by the grating. As a representative example, it is assumed that the grating is the grating of an HDX spectrometer sold by Ocean Optics. Such a spectrometer has a typical spectral resolution of 0.5 - 1 nm. Further, it is assumed that each of the systems of the present embodiment scans the modulation frequency through 10 predetermined modulation frequencies. In this case, the resolution of the entire system is about 0.05 nm to about 0.1 nm.

[0169] Example 2 Experiment An experiment was conducted to examine the ability of a system to determine the spectrum of a light beam. This experiment was aimed at examining Example 3 described later, particularly the theoretical considerations described in Equation 15c therein.

[0170] The experimental setup was the same as in Fig. 2A. Light from a wavelength-tunable laser in the C band (1535 - 1560 nm) was sinusoidally modulated at 0.4 MHz and split into two parallel channels (only one channel is shown in Fig. 2A). One channel was directed to a GePN-type photodiode (model GM3 from GPD Optoelectronics), and the other channel was directed to an InGaAs photodiode (model KPPD-M-2-250S-N from Photop). The outputs of the detectors were monitored, and their RF phase shifts were recorded while scanning the laser wavelength. The results for the InGaAs detector and the Ge detector were plotted in Fig. 5 (upper and lower lines respectively) together with the theoretical predictions formulated in Example 3 below. As shown, a very good agreement was obtained between the results and the theory.

[0171] In the Ge detector, in the wavelength region near 1548 nm, due to the ECD effect,

Equation

[0172] In this example, it is demonstrated that the discovered ECD is real and significant compared to the dispersion fiber. This example also demonstrates a good agreement with the theory.

[0173] Experimental Example 3 Theoretical Considerations This example relates to the PN-type photodiode schematically shown in Fig. 6 and can be regarded as representative of any charge carrier pair generating optical material. In this example, for simplicity, the following structure is considered, that is, an n-type width W doped at a low concentration that is not depleted n represented by, a p-type width W doped at a low concentration that is not depleted p represented by, the width of the depletion region W d represented by, with the total length L = W n + W p and the applied bias voltage V b represented by. The left side of the structure is the cathode (e.g., a heavily doped n region), and the right side is V b anode (e.g., a heavily doped p region). Only as an example, the figure shows W n << W p , and W n , W p >> W d but this does not limit other configurations.

[0174] In the GePN type photodiode (model GM3 manufactured by GPD Optoelectronics) used in the preliminary experiment described in Section 6, light is incident on the n side. The input optical power P in is absorbed, generating electrons and holes, which move to the n side and p side respectively by drift and diffusion. This forms the output current I, I = RP in (1) where R is the responsivity of the detector in units of A / W, λ is in micrometers,

Number

Number

Number

[0175] Therefore, over a differential slice Δx at position x’, the absorbed power is,

Number

Number

Equation

[0176] To express the total current measured at the photodiode output, the contributions of all increments to the current in the range 0 < x' < L are summed. First, the contribution of the total electron current is explained. The contribution of the total hole current is explained below.

[0177] Contribution of electrons (minority charge carriers in the lightly doped p-region) to the total current when the external bias voltage is assumed to be zero The increment of the electron current at x' is, as described by Equation (7), when the electrons propagate leftward from x = x' to the edge of the p-side depletion region, an RF phase shift θ e (x') occurs. Then, the electrons cross the depletion region by the drift current mechanism. This phase shift is θ e (x') = Ωτ e (8) can be expressed as. Here, τ e is the effective propagation time of the electrons, as will be explained below. Only as an example, assuming the external bias is zero, the total electron current, that is, the total diffusion current formed in the non-depletion region with a length ≒ W p < x' < L having a diffusion time τ e, D iff has one main contribution (denoted as Ie). p

[0178] Next, an equation for the total electron current contribution I e is created. The sinusoidal current with x = x' as the origin is from x = x' to x = W n by an amount of

Equation

Number

Number

Number

[0179] The amplitude is

Number

Number

[0180] Contribution of holes (minority charge carriers in the lightly doped n-region) to the total current when the external bias voltage is assumed to be zero Holes are formed on the n side, move to the right by diffusion to the n side of the depletion edge, and the holes cross the depletion region by the drift current mechanism. Similar to the case of the electron current, in this model, most of the hole current is in 0 < x’ < W nIt is assumed that it is a diffusion current formed in the region of. Therefore, if the same processing as above is performed, the total hole AC current is, [Number] can be expressed as. D h is the hole diffusion coefficient, so after integration, I h,ac = Bcos(Ωt - ψ h )(14) becomes. The amplitude is, [Number] and the phase is, [Number] .

[0181] Total amplitude and phase shift of AC current From the above considerations, the total AC current is, I tot,ac = I0cos(Ωt - Φ)(15a) becomes. The amplitude and phase shift of the AC current are, [Number] .

[0182] Therefore, the RF output is a sine wave signal, and its amplitude and phase shift depend on the wavelength through the absorption spectrum α(λ).

[0183] In the above model, the diffusion current formed in the non-depletion region around the PN junction was considered. In addition to this current, since it was assumed that the external bias was zero, there was also a drift current that was ignored. However, if there is a non-zero reverse external bias, the depletion region becomes longer, the voltage drop at both ends of the depletion region becomes larger, and the reverse bias at both ends may form a large drift current. For this reason, additional components are added to the overall phase shift and RF amplitude, but they were not considered in this model for simplicity.

[0184] Example 4 Determination of Fiber Bragg Grating Perturbation The inventor has devised a method and system for obtaining interrogator data from a fiber Bragg grating (FBG) directly from the modulation of light reflected from the grating(s). The inventor has found that there are many advantages to such direct acquisition. First, this technique does not require spectral sweeping, and thus enjoys high noise rejection and fast measurement. Second, this technique can be implemented using relatively low-cost equipment compared to the equipment required for fast time-domain measurements. Third, unlike conventional techniques for resolving time responses in the frequency domain, whose resolution is limited by the fading effect, the technique according to some embodiments of the present invention selects the operating frequency according to the periodicity of the fading effect, thereby improving the resolution.

[0185] FIG. 7 is a schematic diagram of a system 130 suitable for determining the perturbation of an FBG formed in an optical fiber according to some embodiments of the present invention. In a preferred embodiment, the system 130 is used to perform at least some of the operations of the method.

[0186] An optical beam is generated and modulated to provide a modulated optical beam 34. The light can be infrared, visible, or ultraviolet light, as required. Preferably, the light is infrared light.

[0187] The generation and modulation can be performed by an optical modulation system 140. The modulation can be either direct modulation or external modulation and can be of any type known in the art. If direct modulation is employed, the light source 136 receives a modulation signal from the controller 142 and generates a modulated optical beam 134. If external modulation is employed, an unmodulated optical beam 132 is generated by the light source 136 and modulated by an optical modulator 138 that receives a modulation signal from the controller 142. The controller 142 can include dedicated circuitry for generating the modulation signal.

[0188] Modulation can be performed in any frequency range such as radio frequency, but is not limited thereto. When radio frequency modulation is used, the modulation frequency is optionally, preferably, from about 1 kHz to about 40 GHz. In various exemplary embodiments of the present invention, the modulation is sine wave modulation, but in some embodiments, other sine wave modulation waveforms are also contemplated. Also, for example, embodiments in which multi-frequency modulation is used by the sum of sine wave signals each having a different frequency are also contemplated. The modulation includes two or more modulations of amplitude, frequency, and phase, and can be performed to modulate any of the amplitude, frequency, and phase of the optical beam. In a preferred embodiment, at least amplitude modulation is used, and in a more preferred embodiment, only amplitude modulation in which the frequency and phase are not modulated is used.

[0189] This embodiment also contemplates a modulation scan in which the frequency of the modulation is scanned over a plurality of modulation frequencies. The advantages of these embodiments will be described below. However, it should be understood that it is not necessary to use a modulation scan, and the method according to some embodiments of the present invention can also be implemented when the modulation is without frequency scanning.

[0190] In some optional embodiments of the present invention, the optical beam 134 is amplified. This can be achieved, optionally and preferably, by an optical amplifier 150 such as an erbium-doped fiber amplifier (EDFA), a ytterbium-doped fiber amplifier (YDFA), a Raman amplifier, a hybrid Raman / erbium-doped amplifier, a hybrid Raman / ytterbium-doped amplifier, an erbium-ytterbium co-doped fiber amplifier, a neodymium-doped fiber amplifier, a thulium-doped fiber amplifier, etc., but is not limited thereto.

[0191] The modulated optical beam 134 is transmitted through an optical fiber 144 having one or more FBGs 146 formed therein. The light reflected by the FBG(s) 146 is coupled out of the optical fiber 144. The FBG(s) can be fabricated inside the whole or a part of the cross-section of the core, or at the core-cladding interface of the fiber 144, or in other fiber cross-sections known in the art. The optical fiber 144 is optionally, preferably, an optical fiber provided with an FBG sensor or an array of FBG sensors. The FBG 146 is configured to selectively reflect the component of light having a wavelength within a specific Bragg bandwidth centered on a specific Bragg wavelength, allowing other components to continue propagating within the fiber 144. When the optical fiber 144 has a plurality of FBGs, each of at least two FBGs, more preferably each of the FBGs formed in the fiber 144, is configured to selectively reflect different components of light. Thus, each FBG 146 of the fiber 144 is characterized by a Bragg wavelength (and corresponding Bragg bandwidth), and at least two of the FBGs are characterized by different Bragg wavelengths. Shown in FIG. 7 is a fiber with N FBGs characterized by a set of N different respective Bragg wavelengths represented by λ1, λ2, ···, λ N wherein the order of the FBGs need not be in accordance with the λ values.

[0192] In various exemplary embodiments of the present invention, the optical fiber 144 is deployed on or embedded in structures such as aircraft wings, fences, wind turbine blades, buildings, bridges, culverts, tunnel linings, pipelines, rivers, flood control reservoirs, wells, etc., but is not limited thereto.

[0193] The optical in-coupling to and out-coupling from the fiber 144 are optionally, preferably, via one or more optical couplers 148 that provide optical coupling between the system 140 and the fiber 144 and, optionally, preferably, also between the fiber 144 and the optical and electrical analysis system generally indicated at 152. In the schematic diagram shown in FIG. 7, which should not be considered limiting, the optical coupler 148 is shown as an optical circulator having three or more input / output (I / O) ports (three are shown in this embodiment), with at least one port in optical communication with the system 140 and at least one port in optical communication with the fiber 144. In FIG. 7, the optical beam 134 enters the circulator 148 from its first port (1) and exits the fiber 144 from its second port (2). The light reflected by the FBG(s) 146 propagates in reverse within the fiber 144, enters the circulator 148 from its second port (2), and exits from its third port (3). From the third port, the reflected light optionally, preferably, enters the system 152 for performing processing and analysis as will be described in more detail below.

[0194] In some alternative embodiments of the present invention, the modulation is performed after the light exits the fiber 144. In these embodiments, there is no need to perform the modulation before transmitting the light into the fiber. Further, embodiments are contemplated in which the modulation is applied more than once (e.g., before the light is coupled into the fiber and after the light exits the fiber).

[0195] In some embodiments of the present invention, the reflected optical beam is input into the system 20. In the system 20, the reflected optical beam is dispersed according to the discovered effective wavelength dispersion in which the transit time of charge carriers depends on the wavelength. This dispersion increases the group velocity dispersion (GVD) of the reflected optical beam. Preferably, after the dispersion, the magnitude of the GVD of the optical beam is greater (e.g., 2 times, or 4 times, or 8 times, or 10 times greater) than the magnitude of the combined effective GVD of all other components within the system 52.

[0196] The dispersion provided by the charge carrier pair generating optical material of system 20 is typically characterized by a dispersion coefficient DL. Suitable for this embodiment is at least 100P S / nm, or at least 300P S / nm, or at least 1000P S / nm, or at least 1500P S / nm, or at least 2000P S / nm, or at least 2500P S / nm, which can result in a dispersion characterized by a positive or negative dispersion parameter having an absolute value. A charge carrier pair generating material.

[0197] The signal processing system 42 of system 20 determines the phase shift in the modulation of the reflected light from the FBG(s) 146. The inventors have found that the modulation phase shift indicates a perturbation of the FBG, and thus, since the phase shift can be directly determined from the modulation of the light without the need to determine the time domain response of the signal, sensing can be improved.

[0198] When the fiber 144 includes two or more FBGs 146, the system 130 optionally preferably includes an optical demultiplexing system 156 to demultiplex the reflected light beam before entering the system 20. The demultiplexing system 156 can be of any type including but not limited to arrayed waveguide gratings, photonic crystal fibers, etc. Shown in FIG. 7 is an optical demultiplexing system that generates three channels 156 each corresponding to one of the Bragg wavelengths, but it should be understood that the demultiplexing system 156 can generate any number of channels (including a single channel). The system 130 can include a plurality of systems such as the system 20, one for each channel generated by the demultiplexing system 156 (three are shown in FIG. 7, but any number of systems 20 can be employed). In these embodiments, each channel can be input to a different system 20. Alternatively, the system 20 can include a plurality of optoelectronic devices, in which case each channel can be input to a different optoelectronic device 34 of the system 20.

[0199] The inventor has found that even when the fiber 144 includes a plurality of FBGs 146, it is not necessary to demultiplex the reflected light. For example, when using modulation scanning, multiplexing of the modulation frequencies can provide sufficient information regarding the contributions of the plurality of gratings. In these embodiments, the system 20 preferably measures the overall phase shift and the overall magnitude of the reflected light for each modulation frequency. This provides a plurality of overall phase shifts and a plurality of overall magnitudes. Each overall phase shift and overall magnitude represents a wave formed by a plurality of sub-waves corresponding to a plurality of FBGs in the fiber. Thus, each overall phase shift and overall magnitude conveys information regarding the individual phase, wavelength, or frequency shifts caused by the FBGs in the fiber. According to some embodiments of the present invention, the number of different modulation frequencies employed is sufficient to also extract the individual phase, wavelength, or frequency shifts, and optionally the individual magnitudes, from the overall phase shifts and the overall magnitudes. This can be done, for example, by solving a set of equations where the unknowns are the individual phase, wavelength, or frequency shifts and the coefficients and known terms are the overall phase shifts and the overall magnitudes. The inventors have found that for a fiber having N FBGs, it is sufficient to employ N / 2 different modulation frequencies.

[0200] In some embodiments of the present invention, the processing system 42 (not shown) of the system 20 also receives the signal from the reference light detector 162. The reference light detector 162 can receive an optical beam that is reflected by the FBG(s) but does not undergo further dispersion. For example, the beam splitter 157 can be arranged on the optical path of the optical beam emerging from the fiber 144 such that one beam continues as described in more detail above and another beam functions as a reference beam and is directed towards the detector 162 that provides an electrical signal to the processing system 42.

[0201] Based on the phase shift, the perturbation of the FBG is determined. For example, assume that system 140 provides an optical beam that is sinusoidally modulated according to cos(Ωt). Here, Ω is the angular modulation frequency (e.g., within the radio frequency range). The substance 10 (not shown) of system 20 disperses the light such that each component reaches the processing system 42 separately. Further, when the fiber 144 is not perturbed, the optical component reflected from the i-th FBG has an overall modulation phase φ i ) such that it is modulated according to cos(ωt + φ i and exits the substance 10. The signal processing system 42 processes the corresponding electrical signal to determine its modulation parameters.

[0202] Here, assume that a perturbation occurs in the i-th FBG such that it selectively reflects the optical component of wavelength λ i + Δλ i . However, λ i is the wavelength (within the optical range) of the optical component that would have been reflected from the i-th FBG if there were no perturbation in this FBG. Following the dispersion by the substance 10, the i-th component acquires a modulation phase φ i + Δφ i ) such that it is modulated according to cos(Ωt + φ i + Δφ i . Thus, the optical phase shift Δφ i in the modulation is a proxy for the optical wavelength shift Δλ i (or equivalently, the optical frequency shift Δf i = cΔλ i / λ i 2 , where c is the speed of light). If the signal processing system 42 determines that the phase of the i-th component has shifted, the method determines that a perturbation has occurred in the i-th FBG.

[0203] Thus, the system of this embodiment can successfully determine the perturbation based on the phase shift without depending on the optical power of the reflected optical beam. This is different from the conventional techniques that require complex optical power processing operations to determine the perturbation.

[0204] The determined perturbation can be expressed in multiple ways. In some embodiments, the perturbation is represented as a shift in the respective Bragg wavelength (in the above example, Δλ i ). The Bragg shift can be determined, for example, using an empirically generated look-up table that associates between the modulation phase shift Δφ i and the Bragg shift Δλ i . From the expressed value of the Bragg shift, the system can determine, for example, the value of the physical quantity that affects the perturbation of the FBG, which is known in the field of FBG sensors.

[0205] Embodiments are also contemplated in which the perturbation is expressed as a value of a physical quantity without actually determining the Bragg shift. The value of the physical quantity can be determined using an empirically generated look-up table that associates the modulation phase shift with the value of the physical quantity.

[0206] Representative examples of physical quantities that can be determined include, but are not limited to, ambient temperature, pressure applied to the fiber, strain of the fiber, acceleration of the fiber (such as vibration), chemical changes, and other environmental changes around the FBG. Another physical quantity contemplated is the depth of each FBG that can be determined based on the pressure applied thereto.

[0207] The inventors have found that the sensing resolution of the Bragg shift (and thus the resolution of the value of the physical quantity to be determined) can be improved by a judicious choice of the modulation frequency and / or the measurement resolution of the modulation phase shift. Specifically, when representing the measurement resolution of the modulation phase shift as Δφ res , the dispersion parameter characterizing the dispersion as D, and the modulation angular frequency as Ω, at least one of Ω, Δφ res , and D is preferably selected to satisfy the relationship of Δφ res / (D×Ω)≦Δλ res . Here, Δλ res is a predetermined spectral resolution threshold. For example, Δφ resA signal processing system capable of measuring a phase with a resolution of the order of magnitude, and for a substance 10 capable of exerting a dispersion characterized by a dispersion coefficient D, the controller 142 is at least Δφ res / (D×Δλ res ) is configured to generate a modulation signal characterized by an angular modulation frequency Ω.

[0208] Typically, but not necessarily, Δλ res is less than 10 picometers, or less than 1 picometer, or less than 0.1 picometer, or less than 0.05 picometer, for example, 0.01 or less.

[0209] Example 5 Design considerations This example shows that a PN-type photodiode can be used as an adjustable source of optical electron wavelength dispersion (OED) in applications such as high-resolution spectroscopy, environmental sensing, and RF photonic processing, and provides design rules for manufacturing photodiode-based dispersion modules with large, small, zero, and positive or negative OEDs. Below, the modulation-phase shift method was used to measure the OED of the C band of a commercially available germanium PN photodiode. This photodiode exhibits an OED spectral sensitivity of -0.53 deg / nm due to a large OED dispersion of -3.6×10 3 P S / nm, which is equivalent (but with the opposite sign) to about 210 km of SMF28 standard optical fiber. This example also demonstrates the temperature adjustment of OED in germanium photodiodes.

[0210] Figure 8 explains the basic generation source of OED in a PN-type photodiode irradiated with sinusoidally modulated light of frequency Ω = 2πf. This is caused by the wavelength-dependent transit time of charge carriers, resulting in a wavelength-dependent modulation phase shift of the AC current. The modulation phase shift method [9] is used to monitor the modulation phase shift Δθ = ΩΔτ. Here,

Number

[0211] The OED dispersion and sensitivity models of this example are based on the models of the formation and movement of photoinduced charges [3 - 6]. The prominent features of OED in three PN-type photodiodes are 1) the entrance region dominant device, 2) the substrate region dominant device, and 3) the double region device.

[0212] The main dimensionless OED parameter is P≡αW. Here, α is the absorption coefficient depending on λ and W is the width. The parameters of the entrance region, substrate region, and double region are represented by subscripts E, S, and dual respectively. For a device with entrance width and substrate width being W E and W S respectively (the thin intrinsic region of the photodiode is ignored), the parameter q is q≡P E / (P E +P S ) = αW E / α(W E +W S ) = W E / (W E +W S) is defined as. This device has entrance dominance (P S <<P E ) when q → 1 and substrate dominance (P S >>P E ) when q → 0. When 0 < q < 1, the output of the device is the superposition of currents from each of the two regions. With optical modulation I in =I0(1 + me iΩt ), the AC signal of the photodiode output is

Equation

Equation

[0213] Figure 9 plots α -1 (dα / dλ) versus λ for some common materials, showing prominent peaks (negative values) in each band-edge region of the semiconductors.

[0214] In the case of germanium, conveniently, the peak is at the center of the C band. Also, silicon stands out by having broadband OED sensitivity in the near-infrared because its absorption coefficient is significantly lower than that of other common semiconductors.

[0215] Here, we evaluate the first term P(dθ / dP). Since Δθ = ΩΔτ, the dependence on Ω is embedded in P(dθ / dP) in addition to P. The second dimensionless modulation parameter is Mi =ΩW i 2 / D i is defined as. However, D i is the diffusion coefficient of region i and is equal to the modulation phase shift caused by the diffusion current traversing the entire width Wi of region i. The procedure for designing a desired OED device optionally preferably takes into account the effect P of M on the modulation amplitude |f i | and P(dθ / dP).

[0216] Figures 10A and 10B respectively show the AC amplitude versus P tot =P E ), single-region substrate dominance (q = 0 and P tot =P S ), or dual-region (0 < q < 1, P tot =P E +P S ) for any device, and the graph of the OED sensitivity versus P tot and P tot . Next, the main features of the two single-region devices are summarized. From Figure 10B, for both single-region devices, the peak values of P(dθ / dP) (plotted on the left Y-axis, note the inverted values) are approximately equal at about 12.34 degrees, but the signs are opposite at points P E,opt ≒3.3 and P S,opt ≒3.1 respectively. These values are predicted from the model to reach at the respective optimal modulation parameters M E,opt ≒3.3 and MS,opt≒6.5 (see the section on methods below), which is also the point where the amplitude cuts off from the maximum value by [Number] . For both devices, increasing M beyond this value further decreases the amplitude, but in the entrance-dominant device, |P(dθ / dP)| continues to increase, and similarly in the substrate-dominant device, |P(dθ / dP)| decreases.

[0217] The above analysis is for the peak α -1 (dα / dλ) Ge,1560nm =-0.054nm-1 It was applied to germanium with λ = 1560 nm. S OED , Ge,1560nm The value of is plotted on the right Y-axis in Fig. 10B. For both the entrance and substrate-dominated devices, the maximum S OED is |S OED , Ge | max = |P(dθ / dP)α -1 (dα / dλ)|max = |(12.34 deg)(-0.054 nm -1 )| ≒ 0.67 deg / nm is predicted to be (the sign is reversed). Assuming a substrate-dominated device, which is a typical case for commercially available PN photodiodes, W S = P S,opt / α(1560 nm) = 3.1 / 1280 cm -1 = 24 μm. Note that since the allowable error around these optimal values is very wide, the actual width can be made 16 - 48 μm without imposing a severe penalty on the OED sensitivity.

[0218] As another example, for silicon with λ = 900 nm, α Si (900 nm) ≒ 306 cm -1 , α -1 (dα / dλ)Si,900nm = -0.011 nm -1 Therefore, for an optimally designed substrate-dominated device, W S = 3.1 / (306 cm -1 ) ≒ 101 μm, S OED ≒ -0.14 deg / nm. When the DS of silicon is ≒ 10 cm 2 / s, the optimal frequency f = M S D S / (2πW S 2 ) ≒ 104 kHz. When the geometric shape is inverted to form an optimal entrance-dominated device with W E ≒ 108 μm, the sensitivity is the same but the sign is reversed, and this can be achieved with a lower modulation of 45 kHz. These predictions suggest silicon-based photovoltaic cells as inexpensive and sensitive devices for OED.

[0219] One of the favorable features is the S of the entrance and substrate single-region devices OED sign flip, which is easier to understand with reference to FIG. 8. In a typical semiconductor in the UV-IR region, dα / dλ < 0. Therefore, to increase the wavelength, the penetration depth is in inches close to the PN junction in the entrance region, and as a result, the average RF phase delay decreases. Conversely, in the substrate region, as the wavelength becomes longer, the light penetrates further from the PN junction, and the RF phase delay increases.

[0220] Regarding the amplitude characteristics, as shown in FIG. 10A, two single-region devices show significantly different behaviors. In the case of the entrance region device, the Eopt amplitude response at P = 3.3 is close to the maximum achievable value. On the other hand, in the substrate region device, the amplitude at P S,opt = 3.1 is reduced to 23% of the maximum value (at P S = 0.75).

[0221] Thus, when comparing the two single-region device options, it can be seen that the entrance region device is advantageous for high S OED application designs. 1) Both S OED and the AC amplitude are maximized at a common value of P E,opt = 3.3. 2) The modulation frequency required to reach the maximum sensitivity is half of the frequency required for the substrate-dominant device. 3) There is an option to further increase the sensitivity by increasing the modulation degree (however, there is a cost of reducing the amplitude).

[0222] Referring to the dual-region device, FIG. 10B shows the characteristics resulting from the interference between the modulation signals transmitted from the two regions. When q is less than 1, the device begins to exhibit the characteristics of both regions, showing negative and positive S tot values at low P tot values and high P OED values respectively, and P(dθ / dP) = 0 at P tot , ZD(q) Reaches zero OED at the crossover point. This leads to the following two equations. These equations govern the design of the zero-dispersion wavelength λZD of interest and the zero-dispersion device at the selected q.

[0223] W S =P tot , ZD (q)[1 - q] / α(λ ZD ) W E =[q / (1 - q)]·W S For example, a Ge photodiode designed for zero OED with a desired λ ZD = 1560 nm (α(1560 nm) = 1280 cm -1 ), and a selected design value q = 0.01. For example, assume W E =[q / (1 - q)]W S ≒0.01W S In this case, Figure 10B shows that P tot ,ZD ≡ α(λZD)(W E +W S ) = 2.61 and the OED becomes zero. So, the preferred design in this case is W E = 0.2 μm, W S = 10.1 μm.

[0224] The graph also shows the possibility of exceeding the sensitivity of a single region in the region where P opt ≒ 3. As shown in Figure 10A, this is achieved at the expense of a lower signal amplitude.

[0225] The OED was measured using the setup of Figure 11 with a commercially available photodiode. Three experiments were conducted. In each experiment, the phase shift of the AC signal was monitored while varying the wavelength in the C-band between 1530 - 1560 nm. In the first experiment, the optical fiber was a short SMF-28 fiber jumper, and the detector used was a PIN-type InGaAs detector (Tektronix P6703B). In the second experiment, the fiber had a dispersion DL = -680P SIt was replaced with a dispersion compensation fiber module (Photonex EWBDK:680) of / nm, and the same InGaAs photodiode was used for the detector. In the third experiment, a short fiber jumper was used and the detector was changed to a germanium PN photodiode (PDA50B Thorlabs).

[0226] Figure 12A shows the experimental results and the theoretical prediction. Germanium shows a high OED, and the slope within the C band is S OED ≒ -0.53 deg / nm, which is in good agreement with the theory assuming a nominal value of W E = 10 μm and W S = 100 μm. When 400 kHz modulation is used, the measured OED dispersion coefficient,

Number

[0227] Furthermore, as shown in Figure 12B, the temperature adjustment of the OED in the Ge photodiode was demonstrated. The high OED region following the absorption edge region shifts to a higher wavelength as the temperature increases. The measured amount of shift Δλ / ΔT is on the order of 1 nm / °C, which is consistent with the published data of germanium [11 - 13]. Other OED adjustment mechanisms, such as strain or bias voltage adjustment, are also contemplated in some embodiments of the present invention.

[0228] Wavelength dispersion can be used for optical sensing in accordance with various exemplary embodiments of the present invention. By considering the optoelectronic process of a PN photodiode as an adjustable source of wavelength dispersion, the RF photonics of the present embodiment can be used in many applications such as, but not limited to, spectroscopy, environmental sensing, investigation of the physics of optoelectronic processes, etc.

[0229] Method Development of a model for OED sensitivity The following description is based on the continuity equations for the generation and movement of photoinduced charge carriers by diffused PN and PIN type photodiodes [3,4,5,6]. For the purpose of OED of a PN photodiode, in the following description, the drift current is neglected compared to the diffusion current generated in the entrance region and the substrate region. S OED The equations are those developed by the inventors for three types of PN photodiodes, namely, 1) an entrance region dominant device, 2) a substrate region dominant device, and 3) a double region device. In this specification, the parameters of each of these three devices are represented by subscripts E, S, and dual, respectively. The simulations described below were performed using MATLAB (registered trademark) software.

[0230] 1 Single region OED: Entrance region The Sawyer - ReDiker model describes the DC and AC currents formed in the entrance region of a PN photodiode under illumination power modulated in the form of I in =I0(1 + me iΩt )(m is the modulation index). The AC current density component j ac,E is the solution of the diffusion equation for the carrier density P E (x,t) in the entrance region, with dP E / dx = 0 at the entrance x = 0 (assuming surface recombination can be neglected), and P E at the PN junction interface x = W E (W E) specifies the boundary condition of =0. This embodiment contemplates both p-type and n-type for doping. In this specification, the diffusion equation is formulated using three dimensionless parameters as follows. The first parameter is the penetration parameter. P E ≡αW E is the penetration depth α that depends on the wavelength -1 with respect to the entrance width W E ratio. The first parameter is M E ≡ΩW E 2 / D E is the modulation parameter defined by, where D E is the diffusion coefficient of minority carriers. M E represents the modulation phase generated by the modulated mobile carrier density wave that traverses the entire width W E (note that W E 2 / D E is the average diffusion time across the entire entrance region). The third parameter is

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Equation

Equation

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[0231] 2 Single Region OED: Substrate Region The photocurrent in the substrate region is due to the carrier density P E +d < x < W S formed in the region. With the same approach as the entrance region, at x = W S , dP S / dx = 0 (surface recombination can be ignored), and at the PN junction, with the boundary condition P S (x = W S +d) = 0, the substrate AC current density is as follows. E +d)=0, the substrate AC current density is as follows.

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[0232] 3 Double-region OED The two-region device is a device in which the contribution of each region to the overall current and sensitivity cannot be ignored. This depends on the operating wavelength and the width of the region. The OED sensitivity in this case, where the AC current j ac,dual of the two-region device is the sum of the contributions from the two regions, can be expressed based on the above model. In this case, the absorption e-P E generated in the entrance region and resulting in a decrease in the optical power reaching the input to the substrate region (absorption in the thin intrinsic region is ignored) is also considered. Based on the above equations,

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[0233] Although the present invention has been described in relation to its specific embodiments, it is obvious that many alternatives, modifications, and variations will be apparent to those skilled in the art. Therefore, it is intended to embrace all such alternatives, modifications, and variations that fall within the spirit and broad scope of the appended claims.

[0234] All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference herein. Further, the citation or identification of a reference herein shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they shall not necessarily be construed as limiting. Also, the priority claim document(s) of this application are hereby incorporated by reference in their entirety.

[0235] References [1] Fox, M. Optical ProPErties of Solids (Oxford Univ. Press, 2nd Ed., 2010) [2] Agrawal G.P., fiber - Optic Communication Systems (John Wiley & Sons, 4th Ed., 2010). [3] Sawyer D.E. and ReDiker R.H., NarrowBase Germanium PhotoDiodes. Proc. of the IRE, 46, 1122 - 1130 (1958) [4] Lucovsky, G., Lasser, M.E. and Emmons, R.B., Coherent Light Detection in Solid - State PhotoDiodes. Proc. IEEE. 51, 166 - 172 (1963) [5] Lucovsky, G. Schwarz, R.F. and Emmons, R.B., Transit‐Time Considerations in p - i - n Diodes, J. Appl. Phys. 35:3, 622 - 628 (1964) [6] BoWErs, J. and Y. WEy, High - sPEed photodetectors, in Handbook of Optics, Volume I: fundamentals, techniques, and design, M. Bass, ed. (McGraw - Hill, 2nd Ed. 1995). [7] Jang, J.H., Cueva, G., Sankaralingam, R., Fay, P., Hoke, W.E., & Adesida, I., Wavelength dePEndent characteristics of high-sPEed metamorphic photoDiodes. IEEE Photonics Technology Letters, 15(2), 281-283 (2003) [8] Goushcha, A.O., Tabbert, B., On response time of seMiconductor photoDiodes, Opt. Eng. 56, 097101 (2017) [9] Dennis, T. and Williams, P., Achieving high absolute accuracy for Group-delay measurements using the Modulation phase-shift technique, J. Light. Tech. 23, 3748-3754 (2005)

[10] Absorption coefficient data of various semiconductors were obtained from public domain databases such as refractiveindex(dot)info / and www(dot)pveducation(dot)org / pvcdrom / materials / optical-proPErties-of-silicon

[11] Dash, W.C., and Newman, R., Intrinsic optical absorption in single-crystal germanium and silicon at 77K and 300K. Phys. Rev. 99.4, 1151 (1955)

[12] Balbi, M., Sorianello, V., Colace, L., and Assanto, G. Analysis of temPErature dePEndence of Ge-on-Si p-i-n photodetectors, Physica E 41(6), 1086-1089 (2009)

[13] Harris T.R., Optical properties of Si, Ge, GaAs, GaSb, InAs, and InP at elevated temperatures, Thesis, Air Force Institute of Technology (2010)

[14] Yi, X., Chew, S.X., Song, S., Li, L., Tian, X., Nguyen, L., and Minasian, R., Integrated Microwave Photonics for Sensing and Signal Processing. In Optoelectronic Devices and Integration (pp. OW3C-2). Optical Society of America (2019)

[15] K. Yuksel, M. Wuilpart, V. Moeyaert and P. Megret, “Optical frequency domain reflectometry: A review,” in Proc. 11th Int. Conf. Transparent Opt. Netw. (ICTON’09), 1723-727 (2009).

[16] J. Hervas, J., Fernandez-Pousa, C.R., Barrera, D., Pastor, D., Sales, S., & Capmany, J., An interrogation technique of FBG cascades sensors using wavelength to radio-frequency delay mapping, J. Lightwave Tech., 33(11), 2222-2227 (2015)

[17] Ziv Glasser, Gidon Zaychik, Rita Abramov, Daniel Gotliv, and Shmuel Sternklar, Phaseless incoherent optical frequency domain spectroscopy Opt. Lett. 42, 1848-1851 (2017)

[18] Bellido, J.C., & Fernandez-Pousa, C.R., Spectral analysis using a DisPersive Microwave Photonics link based on a broadband chirPed fiber Bragg grating. J. Light. Tech. 33(20), 4207 - 4214(2015)

[19] Li, L., Yi, X., Song, S., Chew, S.X., Minasian, R., & Nguyen, L. Microwave Photonics signal processing and sensing based on optical filtering, Applied Sciences, 9(1), 163(2019)

[20] Zhao, J., Zhang, H., Yang, Z., Xu, J., Xu, T., & Wang, C., Few-Mode fibers With Uniform Differential Mode Group Delay for Microwave Photonic Signal Processing, IEEE Access, 8, 135176 - 135183(2020)

Claims

1. A system for providing information based on the spectral content of an optical signal, comprising: an optical modulator for applying a time-dependent modulation to the optical signal according to at least one sub-optical modulation frequency to provide a modulated optical signal; a photoelectric device configured to receive the modulated optical signal and generate an electrical sensing signal in response thereto, the photoelectric device including the charge carrier pair generation optical material that can generate pairs of charge carriers that result in a net current by the charge carrier pair generation optical material, the transit time of the charge carriers in the charge carrier pair generation optical material being wavelength-dependent, and the electrical signals generated corresponding to different spectral components of the modulated optical signal indicating different modulation parameters, the photoelectric device; a signal processing system configured to process the electrical sensing signal and generate an output correlated with at least one wavelength of the optical signal based on the modulation parameters, the system.

2. The system according to claim 1, wherein the photoelectric device is unbiased.

3. The photoelectric device responds to an electrical bias, and the system includes an electrical drive circuit configured to apply an electrical bias signal to the photoelectric device and scan the DC level of the electrical bias signal, the system according to claim 1.

4. The photoelectric device responds to an electrical bias, and the system includes an electrical drive circuit for applying an electrically biased signal modulated according to a time-dependent modulation to the photoelectric device, and the signal processing system is configured to generate an output correlated with the at least one wavelength based also on the modulation of the electrical bias signal, the system according to claim 1.

5. A system for providing information based on the spectral content of an optical signal, comprising: a photoelectric device configured to receive the optical signal in response to an electrical bias and generate an electrical signal in response; an electrical drive circuit for applying an electrically biased signal modulated according to a time-dependent modulation to the photoelectric device; a signal processing system configured to process the electrical signal and generate an output correlated with at least one wavelength of the optical signal based on the modulation of the electrical bias signal, comprising: The optoelectronic device includes the charge carrier pair generating optical material capable of generating pairs of charge carriers that result in a net current, the transit time of the charge carriers in the charge carrier pair generating optical material is wavelength-dependent, and the electrical signals generated corresponding to different spectral components of the optical signal exhibit different modulation parameters of the time-dependent modulation, the system. **Claim 6** The system according to any one of claims 1 to 4, comprising at least one additional optoelectronic device, the modulated optical signal being also directed to the at least one additional optoelectronic device, and the signal processing system being configured to process an electrical sensing signal generated by the at least one additional optoelectronic device and generate the output also based on the electrical sensing signal generated by the at least one additional optoelectronic device. **Claim 7** The system according to any one of claims 1 to 4, wherein the signal processing system is configured to determine a variable of the sub-optical modulation frequency and generate the output based also on the variable. **Claim 8** The system according to any one of claims 1 to 4, comprising a beam splitting system for splitting the modulated optical signal into two modulated optical signals and directing the two modulated optical signals to opposite sides of the optoelectronic device. **Claim 9** The system according to any one of claims 1 to 4, comprising an additional optoelectronic device and a beam splitting system for splitting the modulated optical signal into two modulated optical signals so as to cancel the optoelectronic wavelength dispersion between the two devices, directing one of the two modulated optical signals to the optoelectronic device, and directing the other one of the two modulated optical signals to the additional optoelectronic device. **Claim 10** The system according to any one of claims 1 to 4, comprising a reflector for reflecting the modulated optical signal to create a multiple optical path within the optoelectronic device. **Claim 11** A method of providing information based on the spectral content of an optical signal, comprising: applying a time-dependent modulation to the optical signal according to at least one sub-optical modulation frequency to provide a modulated optical signal; Receiving the modulated optical signal by means of an optoelectronic device, thereby generating an electrical sensing signal in response to the modulated optical signal, wherein the optoelectronic device includes a charge carrier pair generating optical material capable of generating pairs of charge carriers that result in a net current, the transit time of the charge carriers in the charge carrier pair generating optical material is wavelength-dependent, and the electrical signals generated corresponding to different spectral components of the modulated optical signal exhibit different modulation parameters, said generating; processing the electrical sensing signal to generate an output correlated to at least one wavelength of the optical signal based on the modulation parameter, the method comprising. Claim 12 A method of providing information based on the spectral content of an optical signal, comprising: applying an electrically biased signal modulated according to a time-dependent modulation to an optoelectronic device responsive to an electrical bias; receiving the optical signal by the optoelectronic device during the application of the electrically biased signal, thereby generating an electrical sensing signal in response to the optical signal; processing the electrical sensing signal to generate an output correlated to at least one wavelength of the optical signal based on the modulation of the electrically biased signal, comprising: the optoelectronic device includes a charge carrier pair generating optical material capable of generating pairs of charge carriers that result in a net current, the transit time of the charge carriers in the charge carrier pair generating optical material is wavelength-dependent, and the electrical signals generated corresponding to different spectral components of the optical signal exhibit different modulation parameters of the time-dependent modulation, the method. Claim 13 The method according to claim 11 or 12, comprising reflecting the modulated optical signal to create a multiple optical path within the optoelectronic device. Claim 14 The method according to claim 11 or 12, comprising applying strain or a temperature change to the optoelectronic device to vary the optoelectronic wavelength dispersion provided by the optoelectronic device. Claim 15 The method according to claim 11 or 12, wherein the optical signal is a spectral component of a multi-color beam and is spatially separated from other spectral components of the multi-color beam. Claim 16 The optical signal is multicolor, and the method is the method according to claim 11 or 12, which is applied to generate an output indicating the spectrum of the optical signal.

17. The optical signal indicates a physical characteristic of a sample, and the method is used to determine the physical characteristic or physical state based on the at least one wavelength, and the physical characteristic or the physical state is strain in the sample, a change in strain in the sample, pressure applied to the sample, a change in pressure applied to the sample, temperature of the sample, a change in temperature of the sample, the presence of at least one compound in or near the sample, and an accelerated motion of the sample, and is the method according to claim 11 or 12 selected from the group consisting of.

18. A method of receiving an optical signal modulated to carry a data stream, wherein the optical signal is transmitted via an optical fiber and causes wavelength dispersion in the optical signal, the method comprising: directing the optical signal to an optoelectronic device configured to receive the optical signal and, in response, generate an electrical sensing signal having a pulse width narrower than the pulse width of the optical signal by an amount selected to at least partially compensate for the wavelength dispersion, the optoelectronic device including the charge carrier pair generating optical material that can generate a pair of charge carriers that result in a net current by the charge carrier pair generating optical material, the transit time of the charge carriers in the charge carrier pair generating optical material being wavelength-dependent, and the electrical signals generated corresponding to different spectral components of the optical signal indicating different modulation parameters, the directing; processing the electrical sensing signal to generate an output indicating the data stream. The method includes the above.

19. A sensing method, comprising: applying time-dependent modulation to two optical signals according to at least one sub-optical modulation frequency to provide modulated optical signals; Receiving the modulated optical signal by means of an optoelectronic device, thereby generating an electrical sensing signal in response to the modulated optical signal, wherein the optoelectronic device includes the charge carrier pair generating optical material that can generate pairs of charge carriers that result in a net current by the charge carrier pair generating optical material, the transit time of the charge carriers in the charge carrier pair generating optical material is wavelength-dependent, the electrical signals generated corresponding to the respective different spectral components of the modulated optical signal indicate different modulation parameters, and there is a predetermined relative phase shift between the modulated optical signals, the generating; Processing the electrical sensing signal to determine the phase shift between the optical signals; Generating an output indicating the phase shift; The sensing method comprising:

20. A sensing method, comprising: Dividing an optical signal into two secondary optical signals; Receiving one of the secondary optical signals by an entrance side surface of an optoelectronic device and receiving another one of the secondary optical signals by a substrate side surface of the optoelectronic device, wherein the optoelectronic device includes the charge carrier pair generating optical material that can generate pairs of charge carriers that result in a net current by the charge carrier pair generating optical material, and the transit time of the charge carriers in the charge carrier pair generating optical material is wavelength-dependent, the receiving; Monitoring the electrical signal generated by the optoelectronic device to identify at least one change in the environment in which the optical signal propagates. The sensing method comprising:

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