Patent Description:
Continuing advances in the communications technology and the seemingly insatiable appetite of consumers for services that require more and more bandwidth continue to drive communication service providers to demand that communication equipment companies deliver higher performance, higher bandwidth equipment that occupies less physical space than existing equipment.

All indications are the demand for higher performance, smaller footprint equipment to deliver customer services will not dissipate any time soon, so there remains a continuing need for optical communications systems and devices with higher performance, smaller footprint, and lower cost.

<CIT> discloses a receiver device for receiving as inputs a first beam carrying an optical signal and a second beam carrying a local oscillator. The device mixes the first and second beams into two oppositely phased combined beams and then splits each combined beam into a pair of orthogonally polarized beams that are output. <CIT> discloses a receiver device for receiving as inputs a first beam carrying an optical signal and a second beam carrying a local oscillator. The device mixes the first and second beams into two combined beams and then splits each combined beam into a pair of orthogonally polarized beams that are output.

The present invention addresses the above noted needs and problems by providing optical communication systems, receivers, and methods of receiving according to the claims that involve compact assemblies, such as optical and electrical subassemblies, for quasi-coherent and coherent optical receivers and systems.

Optical systems of the present invention include optical receivers that includes.

In various embodiments, a beam collimator and lens may be employed to collimate the local oscillator light and provide a collimated beam to the prism. Also, lens may also be provided for each orthogonally polarized beam to focus orthogonally polarized beam on the respective opto-electrical converters.

The prism may be generally designed to reflect one of the incoming paths toward a combining surface that combines the local oscillator light and the optical signal. The combined beam then encounters a polarization splitting surface that splits/separates the combined beam into two orthogonally polarized beams. One of the polarized beam may be reflected <NUM> degrees in plane and then both orthogonally polarized beams are reflected <NUM> degrees of out of plane to output each orthogonally polarized beam into substantially parallel optical output paths.

The alignment of the optical components as described above enables a very small form factor for devices of the present invention due to the optical processing of the local oscillator light and optical signal in one plane from one direction and the electrical processing of the signals in a substantially parallel plane and in one direction. In various embodiments, the optical processing and the electrical processing generally proceed in the same direction, but in different planes.

Accordingly, the present disclosure addresses the continuing need for systems and receivers with improved cost and performance.

The accompanying drawings are included for the purpose of exemplary illustration of various aspects of the present invention, and not for purposes of limiting the invention, wherein:.

In the drawings and detailed description, the same or similar reference numbers may identify the same or similar elements. It will be appreciated that the implementations, features, etc. described with respect to embodiments in specific figures may be implemented with respect to other embodiments in other figures, unless expressly stated, or otherwise not possible.

Optical systems <NUM> of the present invention may be employed in various known configurations in uni- or bi-directional systems that may be point or multi-point to point or multi-point configurations with nodes deployed in linear, ring, mesh, and other network topologies and managed via local and/or network management systems. In general, the system <NUM> may be deployed using free space and/or optical fiber, but it may be appreciated that many of the applications may involve fiber optic-based system. See, for example, PCT Application No. PCTIB2018000360 (<CIT>).

Furthermore, the optical system <NUM> may generally support one or more wavelength channels that may be laid out in a channel grid over various ranges in the optical spectrum. For example, single channel system may be operated with a wavelength channel around <NUM> and/or <NUM>. While dense wavelength division multiplexed (DWDM) systems, for example, may divide the optical spectrum ranging nominally from <NUM>-<NUM> (S-band, C-band, L-band) into dozens of wavelength channels having a fixed or variable bandwidths, such as <NUM>, <NUM>, etc., depending upon the design and application of the system <NUM>. For example, the system may be defined with wavelength channels based on the ITU grid, https://www. int/itu-t/recommendations/rec. aspx?rec=<NUM>. Optical signals may be transmitted through the system <NUM> at wavelengths that fall within one of the wavelength channel. While the channel grid may be continuous with adjacent channels sharing a channel edge, the system <NUM> may provide a guard band near the channel edge. The guard band is a wavelength range that is adjacent to the channel edge in which optical signals should not be transmitted used to reduce the amount of interference between signals in adjacent channels.

<FIG> depict exemplary embodiments of optical system <NUM> in point to multi-point links (<NUM>) and point to point links (<NUM>) between nodes. The links may be stand-alone optical communication links or may be part of a passive optical network ("PON") or a network as described in the preceding paragraph that may include passive and active optical switches (OS) and add/drop multiplexers (OADM), optical amplifiers (OA), etc..

In <FIG>, exemplary optical system <NUM> embodiments may include an optical line terminal or regenerator (OLT) <NUM>. The OLT <NUM> may be in uni- or bi-directional optical communication via one or more optical fibers <NUM> with one or more optical network units (ONU) <NUM>. The OLTs <NUM> and ONUs <NUM> may be connected to one or more input/output lines <NUM>, which may be optical and/or electrical depending upon the network implementation.

<FIG> shows exemplary optical system <NUM> embodiments including a point to point link between two OLTs <NUM>. <FIG> embodiments may or may not include optical amplifiers <NUM> depending upon the network configuration.

<FIG> embodiments may be deployed in various layers in the network including the metro and access layers of the network. In the access networks including fronthaul, backhaul and aggregation, the system <NUM> may be operated as a PON or may include line amplifiers <NUM> to provide amplification between the nodes and other active equipment at or between the nodes.

<FIG> shows exemplary OLT <NUM> and ONU <NUM> node embodiments that may include an optical combiner/splitter <NUM> that may combine and/or split optical signals when more than one transmitter or receiver, (OTRx) <NUM> is used in the system <NUM>.

The optical combiner/splitter <NUM> may include passive couplers and wavelength specific multiplexers and demultiplexers depending upon whether the optical system is deployed as a single wavelength and/or wavelength division multiplexed system. For example, the optical system <NUM> may be deployed as a time division multiplexed ("TDM"), wavelength division multiplexed ("WDM"), or time & wavelength division multiplexed ("TWDM") system in which each ONU <NUM> communicating with the OLT <NUM> may use the same or different wavelengths as will be further described herein. It will be appreciated that if a node in the system is only transmitting and/or receiving one channel and only one channel is present on the fiber or free space link <NUM> connecting the nodes, then optical combiner/splitter <NUM> may be used in the nodes.

The transmitters or receivers (OTRx) <NUM> may include only transmitters or receivers, separate transmitters and receivers, or transceivers depending up the system configuration. In various embodiments, it may be cost effective to employ integrated transceivers to reduce cost, but in other embodiments it may be more desirable to employ separate transmitters and receivers, as well as to merely provide for uni-directional communication.

The optical transmitter in the OTRx <NUM> generally include one or more fixed or tunable wavelength optical sources, such as narrow or broad line width lasers. Information in one or more information streams may be imparted to the light, i.e., optical carrier, emitted by the source directly modulating the source, modulating the light using an external modulator, and/or upconverting electrical carriers carrying the information to producing the optical signal carrying the information on one or more wavelengths/frequencies.

The information may be imparted using one or more modulation techniques including amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), etc. or combinations thereof. In addition, the information may be imparted in analog or digital format employing various modulation formats that support two or more modulation levels, e.g., "<NUM>"-states and "<NUM>" states, RZ, NRZ, etc. Advanced/higher-order/multilevel modulation formats, such as duobinary and other higher order constellations, may be used to enable more bits of information per symbol transmitted, or to allow for the use of components with a bandwidth smaller than the equivalent binary signal bandwidth. For example, a system employing four amplitude levels will be able to encode two bits per symbol, a system employing four frequency levels will be able to encode two bits per symbol, a system which independently employs four amplitude and four frequency levels will be able to encode four bits per symbol, and a duobinary or higher order other partial response system will be able to encode one or more bits per symbol using a reduced frequency spectrum. Apart from amplitude and frequency, the information may also be encoded in the phase of the carrier, in the polarization of the carrier, as variations in pulse-width or as variations in pulse position, etc..

It will be further appreciated that the additional signal processing, such as forward error correction (FEC), may be performed in the information before transmission as an optical signal. In various embodiments, error correction and/or testers may be used to provide feedback to control various transmitters and receivers in the system <NUM>.

In various embodiments, the signal may be encoded by one or more simultaneous AM and/or FM devices, such as frequency chirped lasers, directly modulated laser (DML), externally modulated laser (EML), vertical cavity surface emitting laser (VCSEL), etc. Both DMLs and VCSELs have a broad linewidth and are generally low cost. In various embodiments, pure AM may be used for signal modulation through the use an external modulator with a wide variety of lasers, as are known in the art.

Regardless of how the AM and/or FM signal is generated, the frequency modulation is responsible for the different states are converted to different frequencies, whereas the amplitude modulation is responsible for separating the different states in amplitude, thereby conveniently supplying further information of the different states as conventional systems do not include.

The different frequencies, i.e., the different states, are separated by a frequency separation, also called a FM shift. Thus, the FM shift is defined as the frequency separation between the two states of the frequency modulated (FM) signal. As an example, the FM shift is the difference between the "<NUM>"-states and the "<NUM>"-state of the combined AM-FM signal, i.e., the optical signal.

<FIG> shows exemplary embodiments of optical receivers <NUM> that may be employed in the OTRx <NUM> separate from the optical transmitter or as part of a transceiver. It will be appreciated that other optical receivers in the optical system <NUM> may be different from the embodiments shown in <FIG>.

The optical receiver <NUM> generally may include one or more fixed or tunable local oscillator ("LO") optical sources <NUM>, such as lasers of various linewidths, to provide LO light at one or more local oscillator frequencies, which may offset from the frequency of the optical signal, i.e., the LO frequency offset. The optical local oscillator laser (LO) emitting light at an optical frequency (Flo) which is offset from the signal center frequency (Fc) by frequency-offset, or frequency difference, (dF).

A combiner/splitter <NUM> combines an incoming optical signal with the LO light and outputs at least two combined optical signals, e.g., COS1 & COS2 to a corresponding number of optical-to-electrical (OE) converters <NUM>, such as photodiodes. For example, a 2x2 PM coupler may be used or separate combiners and splitters. The OE converters <NUM> output corresponding electrical signals at the frequency of the LO frequency offset, e.g., ES1 & ES2. The corresponding electrical signals may be provided to electrical processing unit <NUM> that may rectify and output the information as an electrical signal on output line <NUM> for further signal processing in the receiver and/or further transmission in or out of the system <NUM>.

<FIG> shows different perspective views of various optical receiver <NUM> embodiments of the present invention. The receiver <NUM> may be a stand-alone device that operates autonomously or a subassembly that operates in conjunction with another optical assemblies. The receiver <NUM> includes an optical assembly <NUM> that performs optical processing of the optical signal and an electrical assembly <NUM> that converts the optical signal to an electrical signal and processes the electrical signal. In order to reduce the physical space occupied by the receiver <NUM>, it may be desirable to package the optical subassembly <NUM> at a <NUM> degree angle to the electrical subassembly <NUM>.

The optical assembly <NUM> may include one or more local oscillator (LO) lasers <NUM>, as well as thermoelectric coolers (TEC) <NUM>, thermistors <NUM> and monitoring photodiodes <NUM> that are provided to control the wavelength and power output from the LO laser <NUM>. While multiple LO lasers <NUM>, coolers <NUM>, thermistors <NUM> and photodiodes <NUM> may be employed, it may be desirable in various applications to use only one to minimize the space consumed by these components.

The output of the LO laser <NUM> may be provided to a beam collimator <NUM> via a beam shaping lens that may include an optical isolator to help protect the LO laser <NUM>. The collimated LO light output from the beam collimator <NUM> is provided to the input of the optical combiner <NUM> on a first optical input path <NUM>i1 and the optical signal being received is provided to the optical combiner <NUM> on a second optical path <NUM>i2 that is parallel to the first optical path <NUM>i1 and in substantially the same plane.

In various embodiments as exemplified in <FIG>, the optical combiner/splitter <NUM> is a free space beam combining and polarization splitting prism. The optical assembly is configured to allow the prism <NUM> to receive the local oscillator light and the optical signal via first and second substantially parallel input paths that are in the same plane.

One of ordinary skill will appreciate that descriptors, such as "substantially", "approximately", etc. are generally meant to be inclusive of "exactly", "identically", etc. For example, the invention may operate as intended or is within the scope of the invention, if an angle is not exactly <NUM> degrees, the light beams are not exactly parallel or coplanar, the LO light is not split <NUM>/<NUM> or oriented at <NUM> degrees, etc. Embodiments including a deviation may be outside the scope of the invention, if the invention no longer functions when implemented with such a deviation. To that end, one of ordinary skill will further appreciate that it is desirable to assemble the optical subassembly <NUM> and electrical subassembly <NUM> in a manner to achieve the relative alignment of components as described herein, which may decrease optical and electrical losses and improve performance.

<FIG> shows the in-plane interactions of incoming light with the prism <NUM>. The prism <NUM> may be generally designed with at least two input paths, <NUM>i1 and <NUM>i2. Light enter the first input path <NUM>i1 encounters a reflective surface A and is reflected toward a combining prism surface B. The light on the <NUM>st path <NUM>i1 is reflected by surface B and combined with light from the second input path <NUM>i2 passing through surface B. The combined light next encounters a polarization splitting surface C in which light in one polarization passes through the surface. Light in the orthogonal state of polarization is reflected by surface C and then reflected by surface D, so as to be traveling in the same direction as the other polarized light beam. Both polarized light beams are reflected substantially <NUM> degrees out-of-plane from the other reflection and are output from the prism. In various embodiments, output focusing lens may provided between the output paths on the prism <NUM> and the opto-electrical converters <NUM> in the electrical assembly <NUM>. The focusing lens may be separate components or integrated on the output surface of the prism <NUM>.

In <FIG> and <FIG> embodiments, the optical signal being received from the transmitter is depicted as entering or being introduced to the prism via the second input path <NUM>i2 with the local oscillator light entering, or being introduced, to the prism <NUM> via the first optical path <NUM>i1. It will be appreciated that while it may be desirable to introduce the optical signal into the second input path <NUM>i2, if the reduced number of reduces the loss through the prism <NUM>, other configurations may be employed.

In various embodiments, the local oscillator light input to the prism may be oriented along an approximately <NUM> degrees angle with respect to the principle axes of the polarizing beam splitter surface of the prism <NUM> to allow the LO light to be split approximately <NUM>/<NUM> between the two polarization states. The LO light is combined with the optical signal in the prism <NUM> and the combined LO-optical signal is split into two orthogonally polarized beams that are output via substantially parallel output paths that are also substantially perpendicular to the input paths, and in the same plane as or a parallel plane to, one of the input paths.

The skilled practitioner will appreciate that the LO light does not need to be linearly polarized. For example, circular or elliptical polarized LO light may be employed. Similarly, if LO light is provided to the prism <NUM> in both polarization states, the align of the LO light at the input has already been addressed.

While the polarization of the local oscillator may be controlled, the polarization of the optical signal is generally not known or controllable in operation. Hence, the optical signal power will be distributed accordingly between the two polarization paths, or arms, depending upon the polarization of the optical signal input into the prism <NUM>. The outputs of the two optical to electrical converters <NUM> will therefore vary in the same way. When the polarization of the signal is completely aligned along one arm, the optical to electrical converter <NUM> associated with that arm will have high output around the offset frequency dF between the local oscillator and optical signal frequencies and the other arm will have zero output around dF. When the signal is evenly distributed between the two arms, the optical to electrical converters <NUM> outputs around dF are equal. By combining the two polarization outputs, the overall system dependence of the polarization of the incoming signal has been reduced.

In various embodiments, the optical to electrical converters <NUM> may be implemented as photodiodes (PD) including APDs, Flip-chip, etc. to convert the first and second combined optical signals into first and second electrical signals. In various embodiments, the PDs <NUM> and electrical processing unit <NUM> have an associated operating bandwidth that may be matched to be approximately equal to or greater than the bandwidth of the incoming optical signal. For example, in various single channel or WDM systems <NUM>, the PD <NUM> bandwidth and electrical processing unit <NUM> may be set at <NUM> to <NUM> times the optical signal bandwidth.

As further shown in <FIG>, the electrical processing unit <NUM> may include transimpedence amplifiers (TIA) <NUM> to amplify the electrical signals from the PDs <NUM> before entering the envelope detectors <NUM> and passing to a clock and data recovery (CDR) circuit <NUM>. The electrical assembly <NUM> may also include a TEC controller <NUM> to control the operation of the TEC <NUM> and processor <NUM>, such as a microcontroller, and associated memory, communication interfaces, etc. as are known in the art to oversee and control some or all of the functions in the assembly <NUM> and communicate with other components in a module and/or the system <NUM>. The various electrical components may be mounted on and connected via a printed circuit board or other substrate <NUM>, as well as being connected separate from the board <NUM>.

The alignment of the optical components and the combination of prism surfaces as described above enables a very small form factor for devices of the present invention due to the optical processing of the local oscillator light and optical signal in one plane from one direction and the electrical processing of the signals in a plane perpendicular to the optical processing plane and in one direction. In various embodiments, the optical processing and the electrical processing proceed in the physical same direction. The receiver <NUM> may be implemented on board with a transmitter assembly to provide a transceiver or may be implemented independently on a line card.

While <FIG> embodiments show the CDR on the board <NUM>, it will be appreciated that the CDR <NUM> may be implemented on another board as the signal has been received and reconstructed at that point.

The foregoing disclosure provides examples, illustrations and descriptions of the present invention, but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. These and other variations and modifications of the present invention are possible and contemplated, and it is intended that the foregoing specification and the following claims cover such modifications and variations.

As used herein, the term component is intended to be broadly construed as hardware, firmware, and/or a combination of hardware and software. Thus, the operation and behavior of the systems and/or methods were described herein without reference to specific software code--it being understood that software and hardware can be designed to implement the systems and/or methods based on the description herein.

Various elements of the system may employ various levels of photonic, electrical, and mechanical integration. Multiple functions may be integrated on one or more modules or line cards being housed in one or more shelves or racks in the system <NUM>.

Hardware processor modules may range, for example, from general-purpose processors and CPUs to field programmable gate arrays (FPGAs) to application specific integrated circuit (ASICs). Software modules (executed on hardware) may be expressed in a variety of software languages (e.g., , computer code), including C, C++, Java™, Javascript, Rust, Go, Scala, Ruby, Visual Basic™, FORTRAN, Haskell, Erlang, and/or other object-oriented, procedural, or other programming language and development tools. Computer code may include micro-code or micro-instructions, machine instructions, such as produced by a compiler, code used to produce a web service, and files containing higher-level instructions that are executed by a computer using an interpreter and employ control signals, encrypted code, and compressed code.

Some implementations are described herein in connection with thresholds. As used herein, satisfying a threshold may refer to a value being greater than the threshold, more than the threshold, higher than the threshold, greater than or equal to the threshold, less than the threshold, fewer than the threshold, lower than the threshold, less than or equal to the threshold, equal to the threshold, etc..

Certain user interfaces have been described herein and/or shown in the figures. A user interface may include a graphical user interface, a non-graphical user interface, a text-based user interface, etc. A user interface may provide information for display. In some implementations, a user may interact with the information, such as by providing input via an input component of a device that provides the user interface for display. In some implementations, a user interface may be configurable by a device and/or a user (e.g., , a user may change the size of the user interface, information provided via the user interface, a position of information provided via the user interface, etc. ). Additionally, or alternatively, a user interface may be pre-configured to a standard configuration, a specific configuration based on a type of device on which the user interface is displayed, and/or a set of configurations based on capabilities and/or specifications associated with a device on which the user interface is displayed.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of possible implementations.

Claim 1:
An optical receiver (<NUM>) comprising:
an optical input configured to receive an optical signal;
at least one local oscillator (<NUM>) configured to provide local oscillator light at a local oscillator frequency,
a free space beam combining and polarization splitting prism (<NUM>) configured to combine the optical signal with the local oscillator light and split the combined optical signal into first and second combined optical signals having orthogonal polarizations,
two opto-electrical converters (<NUM>) configured to convert first and second combined optical signals into first and second electrical signals, and
an electrical combiner (<NUM>) configured to combine the first and second electrical signals into an output electrical signal;
where the optical receiver is configured such that
local oscillator light enters the prism (<NUM>) via a first optical input at an orientation such that it is combined with the optical signal and subsequently the combined optical signal is split between orthogonal polarizations by the prism (<NUM>),
the optical signal enters the prism (<NUM>) via a second optical input that is parallel to the first optical input, the first and second optical inputs lying in an input plane,
the local oscillator light and optical signal being combined and split into first and second combined optical signals by the prism (<NUM>) in the input plane, and output from the prism (<NUM>) in an output plane lying perpendicular to the input plane,
the opto-electrical converters (<NUM>) and the electrical combiner (<NUM>) being in a plane parallel to the input plane.