Methods and apparatus for cavity angle tuning for operating condition optimization

Apparatus, systems, and methods include leveraging the angular dependence of the angle of arrival of the incoming optical signal at an optical resonator and the output response signal to adjust the operating condition of the optical resonator. The optical resonator is dynamically tuned by rotating the optical resonator to optimize signal-to-noise ratio or other parameters for different modulation formats of the incoming optical signal or other different operating conditions.

BACKGROUND

Many optical communication systems manipulate light waves to carry information. For instance, often a light source (e.g., a laser source) is modulated to change various properties of emitted light, such as an amplitude, phase, or frequency of the light to convey information. An optical receiver may receive and demodulate the light waves to recover the information. However, conventional methods of demodulation of coherent signals are either complicated and expensive (e.g., using a local oscillator), or fixed (in data rate and modulation format, for example) and limited.

SUMMARY OF INVENTION

Aspects and embodiments are directed to methods, apparatus, and systems that provide a passive modulation approach that allows for variable data rate, different wavelengths and different modulations formats to be demodulated based on rotating an optical cavity resonator, such as an etalon, that forms part of the demodulator. Certain aspects and embodiments advantageously provide a flexible, low-cost solution that may be particularly application to fiber-based or short-range free-space optical communications, for example.

According to one embodiment, an optical receiver comprises an optical resonator assembly including at least one optical resonator and at least one actuator coupled to the at least one optical resonator and configured to rotate the at least one optical resonator in response to a control signal, the at least one optical resonator being configured to receive an input optical signal, to accumulate optical signal energy inside the at least one optical resonator based at least in part on the input optical signal, and to produce an intensity modulated output optical signal, an intensity modulation of the output optical signal being representative of a modulation of the input optical signal, a detector configured to detect the intensity modulated output optical signal and to identify the modulation of the input optical signal based at least in part on the intensity modulation of the output optical signal, and a controller coupled to the detector and to the optical resonator assembly, the controller being configured to provide the control signal to control the at least one actuator to rotate the at least one optical resonator to tune the at least one optical resonator to a selected operating condition.

In one example, the at least one optical resonator is a Fabry-Perot etalon.

In another example, the at least one optical resonator includes: a first semi-reflective surface positioned to receive the input optical signal, and a second semi-reflective surface positioned facing the first semi-reflective surface, wherein the at least one optical resonator is configured to accumulate the optical signal energy inside the at least one optical resonator and between the first semi-reflective surface and the second semi-reflective surface to approach a steady-state output value of the output optical signal, the intensity modulation of the output optical signal including a series of deviations from the steady-state output value.

In one example, the modulation of the input optical signal is phase modulation, frequency modulation, intensity modulation, or a combination thereof.

In another example, the selected operating condition of the at least one optical resonator is an on-resonance operating condition of the at least one optical resonator.

In one example, the selected operating condition of the at least one optical resonator is an off-resonance operating condition of the at least one optical resonator.

In another example, the at least one optical resonator includes a plurality of optical resonators.

In one example, the at least one actuator includes a plurality of actuators each coupled to at least one optical resonator of the plurality of optical resonators.

In another example, the controller is configured to control the actuator to rotate the at least one optical resonator in response to the modulation of the input optical signal changing.

In one example, the intensity modulated output optical signal is an optical signal reflected from the at least one optical resonator.

In another example, the detector is further configured to identify the modulation of the input optical signal based at least in part on distinguishing between a positive and a negative phase transition of the input optical signal.

In one example, the detector is further configured to identify the modulation of the input optical signal based at least in part on determining a maximum change in intensity of the modulated output optical signal during a phase change of the input optical signal.

According to another embodiment, a method of demodulating a modulated optical signal comprises receiving the modulated optical signal with at least one optical resonator, accumulating optical signal energy inside the at least one optical resonator based at least in part on the modulated optical signal to produce an intensity modulated output optical signal, an intensity modulation of the output optical signal being representative of the modulation of the modulated optical signal, rotating the at least one optical resonator to select an operating condition of the at least one optical resonator, the intensity modulation of the output optical signal being dependent on the operating condition of the at least one optical resonator, detecting the intensity modulated output optical signal, and identifying the modulation of the modulated optical signal based at least in part on the intensity modulation of the output optical signal.

In one example, the at least one optical resonator includes rotating the at least one optical resonator to select the operating condition of the at least one optical resonator based on the modulation of the modulated optical signal.

In another example, the operating condition of the at least one optical resonator is an on-resonance operating condition of the at least one optical resonator, and wherein accumulating the optical signal energy inside the at least one optical resonator includes accumulating resonant optical signal energy inside the at least one optical resonator.

In one example, the operating condition of the at least one optical resonator is an off-resonance operating condition of the at least one optical resonator.

In another example, the at least one optical resonator includes a plurality of optical resonators, and wherein rotating the at least one optical resonator includes individually rotating each of the plurality of optical resonators to select different operating conditions for each of the plurality of optical resonators.

In one example, the intensity modulated output optical signal is an optical signal reflected from the at least one optical resonator.

In another example, identifying the modulation of the modulated optical signal based at least in part on the intensity modulation of the modulated output optical signal includes distinguishing between a positive and a negative phase transition of the modulated optical signal.

In one example, identifying the modulation of the modulated optical signal based at least in part on the intensity modulation of the modulated output optical signal includes determining a maximum change in intensity of the modulated output optical signal during a phase change of the modulated optical signal.

DETAILED DESCRIPTION

Many optical communication systems manipulate light waves to carry information. For instance, often a light source (e.g., a laser source) is modulated to change various properties of emitted light, such as an amplitude, phase, or frequency of the light to convey information. An optical receiver may receive and demodulate the light waves to recover the information. Optical receivers according to certain embodiments use an optical resonator, such as a Fabry-Perot etalon, an optical delay line, or other bulk optical cavity that accumulates energy, as a modulation converter. Using an optical resonator assembly in the demodulator of an optical receiver may offer advantages over conventional demodulation techniques, including the ability to demodulate coherent optical signals with wavefront distortion without the need for adaptive optics or a coherent receiver. The arriving optical signals may be phase modulated, amplitude modulated, or frequency modulated, or may be modulated using a combination of these techniques (e.g., QAM methods), and the optical resonator assembly converts the received phase, amplitude, and/or frequency modulated optical signal into a directly detectable intensity modulated output signal.

The optical resonator(s) within the optical resonator assembly may be sensitive to the angle of arrival of the incoming optical signal, and its output response signal may change as a function of that angle. For example, optical cavities/resonators typically have characteristics, such as the optical path length through the cavity and the resonant condition that may vary as a function of the angle of arrival of optical radiation received by the cavity; changing the resonant condition will change the operating point of the resonator acting as a demodulator. For example, conventionally the resonant condition of a F-P cavity is L=Nλ/2 where λ is the wavelength of light and L is the length of the resonator. According to aspects and embodiments of the disclosure, the optical resonator is operated at the “operating point” L=Nλ/2+ΔL where ΔL is not zero and strictly controlled so as to provide an operating condition. Accordingly, in certain instances, angle tuning (i.e., deliberately orienting or positioning the cavity to receive optical radiation at a given angle of incidence) can be used to change the optical path length through the optical cavity to achieve a certain resonance with a given wavelength of the optical radiation. Aspects and examples described herein provide apparatus, systems, and methods for leveraging this angular dependence to adjust an operating condition of an optical resonator to controllably adjust its transmission and/or reflection characteristics and intensity response to signal modulation changes. For example, according to aspects and embodiments of the disclosure, the optical resonator is operated at the “operating point” L=Nλ/2+ΔL where ΔL is not zero and strictly controlled so as to provide the operating condition. Thus, an optical resonator in an optical receiver can be dynamically tuned to optimize signal-to-noise ratio or other parameters for different modulation formats of an incoming optical signal or different angles of arrival/incidence.

It is to be appreciated that embodiments of the methods and apparatus discussed herein are not limited in application to the details of construction and the arrangement of components set forth in the following description or illustrated in the accompanying drawings. The methods and apparatus are capable of implementation in other embodiments and of being practiced or of being carried out in various ways. Examples of specific implementations are provided herein for illustrative purposes only and are not intended to be limiting. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use herein of “including,” “comprising,” “having,” “containing,” “involving,” and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. References to “or” may be construed as inclusive so that any terms described using “or” may indicate any of a single, more than one, and all of the described terms. Any references to front and back, left and right, top and bottom, upper and lower, and vertical and horizontal are intended for convenience of description, not to limit the present systems and methods or their components to any one positional or spatial orientation. The terms light, light signal, and optical signal may be used interchangeably herein and refer generally to an electromagnetic signal that propagates through a given medium, which may be empty space, e.g., a vacuum, or may be an atmospheric, e.g., air, or other medium, such as fiber or other optics components. The terms “light,” “light signal,” and “optical signal” are not meant to imply any particular characteristic of the light, such as frequency or wavelength, band, coherency, spectral density, quality factor, etc., and may include radio waves, microwaves, infrared, visible, and/or ultraviolet electromagnetic radiation, or other non-ionizing electromagnetic radiation conventionally processed in the field of optics.

FIG. 1is a block diagram of one example of an optical receiver according to certain embodiments. The optical receiver100receives a modulated incoming optical signal110transmitted along a free space signal path (e.g., free space optical, FSO), a fiber coupling, or another waveguide system from a transmitter (not shown). The optical receiver100includes a demodulator120that includes an optical resonator assembly125, a detector assembly130including at least one optical-electrical converter (OEC)135, and a signal processing circuit140. In certain examples, the detector assembly130and the signal processing circuit140may be collectively referred to as a detector. The detector assembly130and the signal processing circuit140may be separate components or may be part of a common module. The optical resonator assembly125is positioned to receive the modulated optical signal110and to produce an output optical signal112that has characteristics representative of the modulation of the modulated optical signal110, as discussed further below. The detector assembly130receives the output optical signal112from the optical resonator assembly125and the at least one OEC135converts the optical signal112into an electrical signal114that can be processed by the signal processing circuit140to produce a decoded information signal116. The decoded information signal116may include the information that was encoded on the modulated optical signal110by the modulation of the modulated optical signal110. The OEC135may include one or more photodiodes, for example, or other components capable of transforming an optical signal into an electrical signal. The signal processing circuit140may include various components, as will be understood by those skilled in the art, such as analog-to-digital converters, filters, amplifiers, controllers, etc., to condition and process the electrical signals received from the detector assembly130to produce the decoded information signal116. The optical receiver100may further include a controller150that may be coupled to the signal processing circuit140and to the optical resonator assembly125and configured to adjust parameters of the optical resonator assembly125to maintain a selected operating condition of the optical resonator assembly125, as discussed in more detail below.

In certain examples, the optical resonator assembly125includes one or more optical resonators configured to convert the modulation of the modulated optical signal110into intensity modulation of the output optical signal112. As noted above, the modulated optical signal110may be phase modulated, amplitude modulated, and/or frequency modulated. As used herein, the term “optical resonator” refers to a component capable of sensing variations, such as frequency variations, amplitude variations, or phase variations in the received incoming optical signal110. Examples of optical resonators may include Fabry-Perot etalons or other types of optical resonators. Each optical resonator in the optical resonator assembly125converts the modulation of the incoming optical signal110in part by interaction of the incoming optical signal110with optical energy built-up in the resonator. Operation of an optical resonator as a phase change detector is discussed below using the example of an etalon; however, those skilled in the art will appreciate that other types of optical resonators can be operated according to similar principles. Further, the optical resonator may respond similarly to amplitude modulated or frequency modulated input optical signals.

Referring toFIG. 2, in certain examples an etalon200is a component having a pair of parallel semi-reflective surfaces212,214that may include an optically transparent material in between, and has a characteristic resonant frequency associated with a certain wavelength of light based upon the spacing (i.e., dimension216) between the semi-reflective surfaces. The surfaces212,214are semi-reflective and also semi-transmissive, in that they allow some light through, and therefore the modulated incoming optical signal110may be allowed into the etalon200and may resonate inside the etalon (i.e., in the interior218between the two semi-reflective surfaces212,214). Additionally, some of the light resonating inside is allowed out of the etalon200(through at least one of the semi-transmissive surfaces). Light emerging from the etalon200is shown, for example, as the output optical signal112. InFIG. 2, the output optical signal112is shown emerging from the etalon200via the second semi-reflective surface214; however, this depiction is merely for ease of illustration and not intended to be limiting; the output optical signal112in certain examples may in addition or alternatively be a reflected signal emerging via the first semi-reflective surface212. The etalon200may have varying levels of reflectivity of the semi-reflective surfaces212,214. In certain examples, the reflectivity may be expressed as a fraction of light amplitude reflected back into the interior218or may be expressed as a fraction of light intensity reflected back into the interior216. The reflectivity of each of the first and second semi-reflective surfaces212,214may be the same or different, and may be any suitable value for a particular implementation.

The etalon200is one example of a suitable optical resonator in accord with aspects and embodiments described herein. Additionally, etalon structures may be formed as a laminate, layer, film, coating, or the like. In some examples, an etalon may include reflective surfaces (including semi-reflective surfaces) that are not co-planar and/or are not co-linear. For example, an interior reflective surface of an etalon may include some curvature, and an opposing surface may also be curved such that a distance between the two surfaces is substantially constant across various regions of the etalon, in some examples. In other examples, an etalon may have non-linear or non-planar surfaces with varying distances between the surfaces at various regions, and may still function as an optical resonator for various wavelengths and at various regions, suitable for use in examples discussed herein. Accordingly, an etalon may be purposefully designed to conform to a surface, or to have various regions responsive to differing wavelengths, or responsive to differing angles of arrival for a given wavelength, in certain examples. In the example shown inFIG. 2, the output intensity/power from the etalon200exhibits a transient disturbance that is a temporary reduction in power; however, in other configurations the transient disturbance may instead be a temporary increase in response to a phase (or amplitude or frequency) transition occurring in the modulated incoming optical signal110.

The optical resonator assembly125may include one or more etalons200, or other types of optical resonators that operate similarly to convert the modulation of the incoming optical signal110into the intensity-modulated output optical signal112which may then be detected and processed to recover the information encoded in the incoming optical signal110. As discussed above, in various examples, each optical resonator within the optical resonator assembly125may have one or more characteristic resonant frequencies (alternatively referred to as a characteristic resonant wavelength). When the frequency of the incoming optical signal110corresponds to the characteristic resonant frequency of the optical resonator, optical signal energy accumulates to build-up resonating optical signal energy inside that optical resonator, as discussed above.

In certain examples, the at least one optical-electrical converter (OEC)135includes an additional OEC135(not shown) that is provided in the optical receiver100discussed above with reference toFIG. 1. The additional OEC135is configured to receive a reflected signal (not shown) from the optical resonator assembly125. In an example, at least a portion of the arriving signal that is reflected off the first semi-reflective surface212is received by the additional OEC135. Due to the complimentary nature of the transmitted and reflected signals, additional information of the arriving optical signal may be provided to the controller150. The additional OEC135may include one or more photodiodes, for example, or other components capable of transforming the reflected optical signal into an electrical signal. According to certain aspects and examples, the controller150may be coupled to the signal processing circuit140and to the optical resonator assembly125and configured to adjust parameters of the optical resonator assembly125to maintain a selected operating condition of the optical resonator assembly125based on the output optical signal112. In some embodiments, the output signal112may be the transmitted optical signal, the reflected signal, or any other signal that results from the interaction of the incoming optical signal110with energy stored within an optical resonator, such as etalon200.

FIG. 2shows a graph220of the modulated incoming optical signal110, showing a phase change in the optical signal110. The graph220plots the phase (vertical axis) of the optical signal110over time (horizontal axis), showing a phase transition of pi (180 degrees) at point222.FIG. 2also shows a graph230of optical signal intensity (as output power) emerging from the etalon200during the phase transition in the received optical signal210. At region232the etalon200is in a steady-state resonance condition wherein a steady intensity of light emerges. At point234, corresponding to point222in the graph220, a phase transition occurs in the arriving optical signal110, temporarily disrupting the steady-state and causing a change in the emerging light intensity. In some examples, the change is an increase in the emerging light intensity. In other examples, the change is a decrease in the emerging light intensity. During successive reflections inside the etalon200, and indicated region236in the graph230, resonance is re-establishing, and the emerging light intensity increases until, at point238, a steady intensity of light emerges when the etalon200has returned to a steady-state condition. Thus, variations in the intensity of the output optical signal112from the etalon200indicate that a transition occurred in the incoming optical signal110, such as a phase transition due to phase modulation of the optical signal110. As discussed above, the etalon200may respond similarly to frequency and/or amplitude transitions that correspond to frequency or amplitude modulation, respectively, of the optical signal110. Thus, the etalon200functions as a modulation converter for the optical signal110. The output optical signal112may therefore carry the same information content as the arriving optical signal110, but in an intensity modulated form, rather than a phase modulated form, for example. Further, the etalon200may function as a modulation converter when operating at various operating conditions, as discussed further below.

The resonance condition of the optical resonator depends on the wavelength, k, of the arriving optical signal110and the optical path length of the optical resonator. For example, referring again toFIG. 2, a tuned etalon200may have an interior dimension216that is selected such that the optical path length, L, (i.e., based upon the speed of light in the material of the interior218) is an integer number of half-wavelengths, e.g., L=nλ/2, a resonant condition, where n is a positive integer. The optical path length is also dependent on the angle of incidence of the arriving optical signal110because that angle determines the angle at which the optical signal110travels between the first and second semi-reflective surfaces212,214. For a given wavelength, the optical path length of the etalon200is shortest for normal incidence, and increases as the angle of incidence of the optical signal110changes away from normal. For example, while the optical path length of the etalon200may be precisely L=nλ/2 (or some other chosen value) for a selected “baseline” angle of incidence, a, of the optical signal110, the optical path length changes to L′=nλ/2±ΔL when the angle of incidence changes (e.g., α′=α±Δα), where ΔL is a function of Δα. The dependence of the optical path length of the etalon on the angle of incidence or angle of arrival of the incoming optical signal110in turn causes the tuning or resonance of the etalon200to be dependent on the angle of arrival of the incoming optical signal110. Thus, etalon200is sensitive to the angle of arrival of the incoming optical signal110and, in general, the response of the etalon200, or intensity/amplitude of the output optical signal112, changes as a function of that angle.

FIG. 3shows a representation of a steady-state intensity transmission pattern produced300by an example of the etalon200in response to receiving the incoming optical signal110. The pattern is plotted in angular space, such that each point on the two-dimensional plot corresponds to an angle of arrival of the incoming optical signal110along the x and y axes. For any given angle of arrival, that point on the plot provides the amount of light, ranging from 1 to a minimum value (which may be near zero or some other minimum value). Thus, the pattern shows the transmitted intensity of light at approximately 1550 nm from the etalon200as a function of angle. In this example, the etalon200has an interior dimension216of approximately 10 millimeters (mm). Light and dark regions in the pattern300indicate constructive interference (peaks) and destructive interference (valleys) fringes, respectively. As shown, for a continuous wave optical beam, the fringes are symmetric and, in this example, form a circular pattern.

FIGS. 4A and 4Bare graphs showing a plot of the transmission characteristic changes for positive and negative phase changes for examples of the etalon200. More specifically,FIG. 4Ais a graph showing an example of the maximum change in intensity during phase change in the incoming modulated beam of the output optical signal112(as a fraction of the intensity of the input optical signal110) as a function of angle (the angle of incidence of the input optical signal110). In this example, the incoming optical signal110is a phase modulated signal, and in the graph, trace412represents the output optical signal112responsive to a +Pi phase change in the incoming optical signal110and trace414represents the output optical signal112responsive to a −Pi phase change in the incoming optical signal110. In this example, the etalon200has an interior dimension216of 10 mm, and is tuned for an operating condition at normal incidence of the incoming optical signal110.

As shown inFIG. 4A, the intensity output, or transmission response of etalon200to a given phase change in the incoming optical signal110is dependent on the angle of incidence. Thus, the etalon200may be tuned or adjusted to produce a particular desired intensity output change in response to a given phase change by controlling the angle of incidence of the incoming optical signal110at the etalon200. In one example, this angular tuning can be achieved by rotating the etalon200. For example, referring toFIG. 4A, to achieve a maximum intensity output from the etalon200in response to a +Pi phase change, the etalon can be rotated such that the incoming optical signal110is incident at an angle of approximately 8 milliradians (mrad) or 16 mrad, etc.

As also may be appreciated fromFIGS. 3 and 4A, for a given amount of transmitted continuous-wave (CW) light in the optical signal110, it may be unclear whether the angle of arrival of the incoming optical signal110is on a positive or negative slope of a given interference fringe. This ambiguity can be removed using a phase modulated incoming optical signal110. For example, referring toFIG. 4A, traces412and414, corresponding to +Pi and −Pi phase transitions in the incoming optical signal110, respectively, overlap at certain incidence angles. Thus, by controlling the angle of incidence, for example, by rotating the etalon200as discussed above, this ambiguity can be removed by adjusting the etalon to an angle where there is a significant, or at least reliably observable, difference in the relative amplitudes of the transmission response to positive and negative phase changes of the incoming optical signal110.

FIG. 4Bis a graph similar toFIG. 4A, showing another example of the change in intensity of the output optical signal112(as a fraction of the intensity of the incoming optical signal110) as a function of angle (the angle of incidence of the incoming optical signal110). In this example, the incoming optical signal110is again a phase modulated signal, and trace422represents the output optical signal112responsive to a +Pi phase change in the incoming optical signal110and trace424represents the output optical signal112responsive to a −Pi phase change in the incoming optical signal110. In this example, the etalon200has an interior dimension216of 10 mm, and is detuned for an off-resonance operating condition at normal incidence of the input optical signal110. As may be seen with reference toFIGS. 4A and 4B, the same phase-to-intensity responses can be achieved for both on-resonance and off-resonance operating conditions of the etalon200at different angles.

FIGS. 4A and 4Bare example plots of the transmission response of etalon200to a given phase change in the incoming optical signal110. Other plots similar to4A and4B can be generated based on the reflection response of etalon200to a given phase change in the incoming optical signal110. In some embodiments, similar plots for the reflection characteristics for +Pi and −Pi phase changes for a given optical resonator are generated to remove ambiguity between a +Pi and −Pi phase change by adjusting the etalon200to an angle where there is a significant, or at least reliably observable, difference in the relative amplitudes of the reflection response to positive and negative phase changes of the incoming optical signal110.

According to certain aspects and embodiments, due to the relationship between the angle of arrival of the incoming optical signal110and the operating point or transmission response of the etalon200, by rotating the etalon, the operating condition of the etalon and its associated transmission characteristic can be dynamically changed. For example, the etalon200can be varied between different operating conditions. Similarly, a particular desired intensity output in response to any given phase, amplitude or frequency shift in the input optical signal (corresponding to modulation of the incoming optical signal110) can be achieved by rotating the etalon200to the corresponding angle that produces the desired result. Depending on the modulation format of the input optical signal, it may be desirable to optimize the etalon200to different operating points to produce different responses. For example, in certain modulation schemes, it may be beneficial to be able to distinguish between positive and negative phase transitions. In other examples, it may be beneficial to have a maximum intensity of the output optical signal112correspond to a certain transition (e.g., a phase transition of a particular amount and/or in a particular direction) and a minimum intensity correspond to a different type of transition. Knowing the angular dependence of the transmission characteristic of the etalon200for any given modulation transition, allows the etalon200to be rotated to produce the desired response. The angle of rotation can be dynamically changed to adapt to different incoming optical signals110with different modulation formats, for example, or changing environmental conditions.

FIG. 5is a functional block diagram of another example of the optical receiver100discussed above with reference toFIG. 1. In this example, the optical resonator assembly125includes at least one actuator160coupled to a corresponding at least one optical resonator (e.g., etalon)200. The actuator160is coupled to the controller150. The controller150may provide a control signal to the actuator160to control the actuator to rotate the optical resonator200to a desired angle so as to achieve a desired operating condition of the optical resonator200. In certain examples in which the optical resonator assembly125includes multiple optical resonators200, the optical resonators may be coupled to the same actuator160, such that all the optical resonators200are rotated by the same amount and at the same time, under the control of the controller150. For example, individual ones of the multiple optical resonators200may be tuned to different baseline operating conditions to provide a suite of responses that can be changed together by rotating the collection of optical resonators200using the actuator160. In other examples, the optical resonator assembly125may include multiple actuators160, each coupled to one or more optical resonators200. In such examples, individual ones or groups of optical resonators can be rotated to tune their desired operating conditions independently of other optical resonators200in the optical resonator assembly125. It should be noted that in certain circumstances, such as when the wavefront is distorted, rotating the etalon(s)200may reduce the overlap of spatial coherence of the transmitted optical signal112. However, in fiber-coupled optical receivers, there is little to no wavefront distortion from the optical fiber(s) that input the incoming optical signal110to the etalon(s) as the fiber(s) can be configured to provide very high beam quality, and therefore the output optical signal112may retain spatial coherency, even with rotation of the etalon(s)200. Accordingly, embodiments of the optical receiver100may be particularly well suited to fiber-based applications or short-range free-space optical communications applications in conditions with low turbulence, where the beam of the incoming optical signal110is coherent with excellent beam quality.

Thus, aspects and embodiments provide an optical receiver100that leverages the response of one or more etalons200to convert the modulation (phase, frequency, and/or amplitude) of an incoming optical signal110into an intensity-modulated output signal112that can be received and decoded to extract the information encoded on the modulated incoming optical signal110. Using one or more optical resonators that can be rotated to tune their operating conditions, a highly flexible, compact, and robust optical receiver100may be provided, having the capability to dynamically adjust to different modulation formats or applications.