Optical transmission system, optical receiver, and method for combining and receiving optical signals

Abstract

Optical systems, receivers, devices, and methods include free-space beam combining and polarization splitting prisms that receive local oscillator light and an optical signal in substantially parallel input paths in the same plane and output two orthogonally polarized beams in substantially parallel output paths in a plane substantially perpendicular to the input paths. Light in one of the incoming paths is reflected 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 the combined beam into two orthogonally polarized beams. One of the polarized beams can be reflected at 90 degrees within the plane, and then the two orthogonally polarized beams are reflected at 90 degrees out of the plane, thereby outputting the respective orthogonally polarized beams into substantially parallel optical output paths.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62 / 831,255, filed on April 9, 2019, the entire contents of which are incorporated herein by reference.

[0003] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0004] not applicable.

[0005] Reference to a sequence listing, table or computer program listing a CD-ROM appendix

[0006] not applicable.

[0007] Background of the Invention Technical Field

[0008] The present invention relates generally to optical systems with improved performance. More particularly, the present invention relates to optical transmission systems, receivers, devices and methods that enable quasi-coherent and coherent detection of optical signals using compact optical devices. Background Art

[0009] Continuous advances in communications technology and seemingly insatiable consumer demand for services that require more and more bandwidth continue to drive communications service providers to demand from communications equipment companies to provide higher performance, higher bandwidth equipment that takes up less physical space than existing equipment.

[0010] All indications are that the demand for higher performance, smaller footprint equipment to provide customer service will not disappear any time soon, and thus there remains a continuing need for optical communications systems and devices with higher performance, smaller footprint, and lower cost. Summary of the invention

[0011] The present invention addresses the above-mentioned needs and problems by providing communication systems, receivers, devices and methods involving compact components, such as optical and electrical sub-components, for quasi-coherent and coherent optical receivers and systems.

[0012] The optical system of the present invention comprises a light receiver, which may include:

[0013] Optical signal input port for receiving optical signals

[0014] a local oscillator input for receiving local oscillator light from one or more local oscillators;

[0015] a free-space beam combining and polarization splitting prism that receives the local oscillator light and the optical signal in substantially parallel input paths that are in the same plane and outputs two orthogonally polarized light beams in substantially parallel output paths that are substantially perpendicular to the plane of the input paths, both light beams including at least a portion of the local oscillator light and at least one light beam including the optical signal;

[0016] Two or more optoelectronic converters, each optoelectronic converter positioned to receive a different one of the orthogonally polarized beams from the prism output path.

[0017] In various embodiments, a beam collimator and a lens may be used to collimate the local oscillator light and provide the collimated beam to the prism. In addition, a lens may be provided for each orthogonally polarized beam to focus the orthogonally polarized beam on a corresponding photoelectric converter.

[0018] The prism can be 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 separates / splits the combined beam into two orthogonally polarized beams. One of the polarized beams can be reflected at 90 degrees within the plane, and then the two orthogonally polarized beams can be reflected at 90 degrees out of the plane, thereby outputting the individual orthogonally polarized beams into substantially parallel optical output paths.

[0019] The alignment of the optical components as described above enables the device of the present invention to achieve a very small form factor due to the optical processing of the local oscillator light and the optical signal in one plane from one direction and the electrical processing of the signal in a substantially parallel plane and in one direction. In various embodiments, the optical processing and the electrical processing are typically in the same direction, but in different planes.

[0020] Thus, the present disclosure addresses the continuing need for systems and receivers with improved cost and performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings are included to illustrate various aspects of the invention by way of example and not to limit the invention, in which:

[0022] Figure 1 and Figure 2 Exemplary optical system implementations are shown.

[0023] Figure 3 An exemplary optical line terminal / regenerator implementation is shown.

[0024] Figure 4 as well as FIG. 5A to FIG. 5CAn exemplary optical receiver implementation is shown.

[0025] Figure 6 Shows such as FIG. 5A to FIG. 5C A cross-sectional view of an exemplary free-space prism embodiment is shown.

[0026] In the drawings and detailed description, the same or similar reference numerals may identify the same or similar elements. It should be appreciated that unless explicitly stated or not otherwise feasible, implementations, features, etc. described with reference to an embodiment in a particular figure may be implemented with reference to other embodiments in other figures. DETAILED DESCRIPTION

[0027] The optical system 10 of the present invention can be used in various known configurations in unidirectional or bidirectional systems, which can be point or multipoint to point or multipoint configurations, where nodes are deployed in linear, ring, mesh and other network topologies and managed via local and / or network management systems. Generally, the system 10 can be deployed using free space and / or optical fiber, but it will be appreciated that many applications can involve optical fiber-based systems. For example, see PCT Application No. PCTIB2018000360 (WO2018172847).

[0028] In addition, the optical system 10 can generally support one or more wavelength channels, which can be arranged in a channel grid on various ranges in the spectrum. For example, a single-channel system can work with wavelength channels centered at 1310nm and / or 1550nm. A dense wavelength division multiplexing (DWDM) system can, for example, divide the spectrum from a nominal range of 1490nm to 1625nm (S band, C band, L band) into dozens of wavelength channels with fixed or variable bandwidths (such as 50GHz, 100GHz, etc.), depending on the design and application of the system 10. For example, the system can be defined using wavelength channels based on the ITU grid, https: / / www.itu.int / itu-t / recommendations / rec.aspx? rec=11482. An optical signal can be transmitted through the system 10 at a wavelength that falls within one of the wavelength channels. Although the channel grid can be continuous with adjacent channels that share the channel edge, the system 10 can provide a guard band near the channel edge. A guard band is a wavelength range adjacent to a channel edge where optical signals should not be transmitted, and is used to reduce the amount of interference between signals in adjacent channels.

[0029] Figure 1 and Figure 2An exemplary embodiment of an optical system 10 employing point-to-multipoint links (1) and point-to-point links (2) between nodes is depicted. The links may be stand-alone optical communication links, or may be part of a passive optical network ("PON"), or may be part of a network as described in the previous paragraphs that may include passive and active optical switches (OS) and add / drop multiplexers (OADMs), optical amplifiers (OAs), etc.

[0030] exist Figure 1 , an exemplary optical system 10 embodiment may include an optical line terminal or regenerator (OLT) 12. The OLT 12 may be in unidirectional or bidirectional optical communication with one or more optical network units (ONUs) 16 via one or more optical fibers 14. The OLT 12 and ONUs 16 may be connected to one or more input / output lines 18, which may be optical and / or electrical depending on the network implementation.

[0031] Figure 2 An exemplary optical system 10 embodiment is shown including a point-to-point link between two OLTs 12. Depending on the network configuration, Figure 1 and Figure 2 Implementations may or may not include the optical amplifier 20 .

[0032] You can Figure 1 and Figure 2 Embodiments are deployed in various layers in the network, including the metro layer and access layer of the network. In an access network including fronthaul, backhaul, and aggregation, the system 10 may operate as a PON, or may include line amplifiers 20 to provide amplification between nodes and other active devices located at or between nodes.

[0033] Figure 3 An exemplary OLT 12 and ONU 16 node implementation is shown, which may include an optical combiner / splitter 22 that may combine and / or split optical signals when more than one transmitter or receiver (OTRx) 24 is used in the system 10 .

[0034] Depending on whether the optical system is deployed as a single wavelength and / or wavelength division multiplexing system, the optical combiner / splitter 22 may include passive couplers and wavelength-specific multiplexers and demultiplexers. For example, the optical system 10 may be deployed as a time division multiplexing ("TDM"), wavelength division multiplexing ("WDM"), or time and wavelength division multiplexing ("TWDM") system, where the various ONUs 16 communicating with the OLT 12 may use the same or different wavelengths, as will be further described herein. It should be appreciated that an optical combiner / splitter 22 may be used in a node if the node in the system transmits and / or receives only one channel and there is only one channel on the optical fiber or free space link 14 connecting the nodes.

[0035] Depending on the system configuration, the transmitter or receiver (OTRx) 24 may include only a transmitter or receiver, a separate transmitter and receiver, or a transceiver. In various embodiments, it may be cost-effective to use an integrated transceiver to reduce costs, but in other embodiments, it may be more desirable to use a separate transmitter and receiver and only provide one-way communication.

[0036] The optical transmitter in the OTRx 24 typically includes one or more fixed or tunable wavelength light sources, such as narrow or broad linewidth lasers. Information in one or more information streams may be imparted to the light emitted by the source (i.e., an optical carrier) by directly modulating the source, modulating the light using an external modulator, and / or up-converting an electrical carrier carrying the information to generate an optical signal carrying the information at one or more wavelengths / frequencies.

[0037] The information may be imparted using one or more modulation techniques including amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), etc. or a combination thereof. In addition, the information may be imparted in an analog or digital format using various modulation formats that support two or more modulation levels (e.g., a "0" state and a "1" state, RZ, NRZ, etc.). Advanced / higher order / multi-level modulation formats (such as duobinary and other higher order constellations) may be used to enable more bits of information to be transmitted per symbol, or to allow the use of components with a bandwidth less than that of an equivalent binary signal. For example, a system that employs four amplitude levels will be able to encode two bits per symbol, a system that employs four frequency levels will be able to encode two bits per symbol, a system that independently employs four amplitude levels and four frequency levels will be able to encode four bits per symbol, and other partial response systems of duobinary or higher order will be able to encode one or more bits per symbol using a reduced spectrum. In addition to amplitude and frequency, information may also be encoded in the phase of the carrier, in the polarization of the carrier, as a change in pulse width, or as a change in pulse position, etc.

[0038] It should also be appreciated that additional signal processing such as forward error correction (FEC) may be performed on the information before it is transmitted as an optical signal. In various embodiments, error correction and / or testers may be used to provide feedback to control the various transmitters and receivers in system 10.

[0039] 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 lasers (DMLs), externally modulated lasers (EMLs), vertical cavity surface emitting lasers (VCSELs), etc. Both DMLs and VCSELs have wide line widths and are generally low cost. In various embodiments, pure AM may be used for signal modulation by using an external modulator with a wide variety of lasers, as known in the art.

[0040] Regardless of how the AM and / or FM signals are generated, frequency modulation is responsible for converting the different states to different frequencies, while amplitude modulation is responsible for separating the different states in amplitude, thereby conveniently providing further information about the different states that conventional systems do not include.

[0041] Different frequencies (i.e., different states) are separated by frequency separation (also called FM shift). Thus, FM shift is defined as the frequency separation between two states of a frequency modulated (FM) signal. As an example, FM shift is the difference between the "0" state and the "1" state of a combined AM-FM signal (i.e., optical signal).

[0042] Figure 4 An exemplary embodiment of an optical receiver 30 is shown, which may be used in the OTRx 24 separately from the optical transmitter or as part of the transceiver. It should be appreciated that other optical receivers in the optical system 10 may be used in conjunction with the optical transmitter 30. Figure 4 The embodiments shown are different.

[0043] The optical receiver 30 may generally include one or more fixed or tunable local oscillator ("LO") light sources 32, such as lasers of various line widths, to provide LO light at one or more local oscillator frequencies that may be offset relative to the frequency of the optical signal, i.e., the LO frequency offset. An optical local oscillator laser (LO) emits light at an optical frequency (Flo) that is offset relative to a signal center frequency (Fc) by a frequency offset or frequency difference (dF).

[0044] The combiner / splitter 34 combines the incoming optical signal with the LO light and outputs at least two combined optical signals (e.g., COS1 and COS2) to a corresponding number of optical-to-electrical (OE) converters 36, such as photodiodes. For example, a 2x2 PM coupler or a separate combiner and splitter may be used. The OE converters 36 output corresponding electrical signals, e.g., ES1 and ES2, at frequencies offset from the LO frequency. These corresponding electrical signals may be provided to an electrical processing unit 38, which may rectify the information as electrical signals and output them via output lines 18 for further signal processing in a receiver and / or further transmission in or outside the system 10.

[0045] FIG. 5A to FIG. 5C Different perspective views of various optical receiver 30 embodiments of the present invention are shown. The receiver 30 can be a stand-alone device that works autonomously or a subassembly that works in conjunction with another optical assembly. The receiver 30 includes an optical assembly 40 that performs optical processing of the optical signal and an electrical assembly 50 that converts the optical signal into an electrical signal and processes the electrical signal. In order to reduce the physical space occupied by the receiver 30, it may be desirable to package the optical subassembly 40 at a 90 degree angle to the electrical subassembly 50.

[0046] The optical assembly 40 may include one or more local oscillator (LO) lasers 32, as well as a thermoelectric cooler (TEC) 42, thermistor 44, and monitoring photodiode 46, which are provided to control the wavelength and power output of the LO laser 32. Although multiple LO lasers 32, coolers 42, thermistors 44, and photodiodes 46 may be employed, in various applications it may be desirable to use only one to minimize the space consumed by these components.

[0047] The output of the LO laser 32 may be provided to a beam collimator 48 via a beam shaping lens, which may include an optical isolator to help protect the LO laser 32. The collimated LO light output from the beam collimator 48 is provided to the first optical input path 34. i1 The optical signal is provided to the input end of the optical combiner 34 and the optical signal being received is transmitted to the input end of the optical combiner 34. i2 Provided to the light combiner 34, the second light path is parallel to the first light path and is substantially in the same or parallel plane.

[0048] In such FIG. 5A to FIG. 5C In various illustrated embodiments, the optical combiner / splitter 34 is a free space beam combining and polarization splitting prism. The optical components are configured to allow the prism 34 to receive the local oscillator light and the optical signal via first and second substantially parallel input paths in the same or parallel planes.

[0049] One of ordinary skill will appreciate that descriptors such as "substantially," "approximately," and the like are generally meant to include "exactly," "the same," and the like. For example, the present invention may work as intended or be within the scope of the present invention assuming that the angles are not exactly 90 degrees, the beams are not exactly parallel or coplanar, the LO light is not split 50 / 50 or oriented at 45 degrees, and the like. If the present invention no longer functions when implemented with a certain deviation, then an embodiment including such a deviation may be outside the scope of the present invention. To this end, one of ordinary skill will also appreciate that it is desirable to assemble the optical subassembly 40 and the electrical subassembly 50 in a manner that achieves relative alignment of the components as described herein, which may reduce optical and electrical losses and improve performance.

[0050] Figure 6 The in-plane interaction of the incoming light with the prism 34 is shown. The prism 34 can generally be designed with at least two input paths 34 i1 and 34 i2 Enter the first input path 34 i1 The light encounters the reflective surface A and is reflected toward the combined prism surface B. The first path 34 i1 The light on the surface is reflected by the surface B and combines with the light from the second input path 34 passing through the surface B. i2 The combined light then encounters polarization splitting surface C, through which light in one polarization state passes. Light in an orthogonal polarization state is reflected by surface C and then by surface D so as to travel in the same direction as the other polarized light beam. Both polarized light beams are reflected out of the plane at substantially 90 degrees relative to the other reflection and are output from the prism. In various embodiments, an output focusing lens may be provided between the output path on the prism 34 and the photoelectric converter 36 in the electrical assembly 50. The focusing lens may be a separate component or integrated on the output surface of the prism 34.

[0051] In Figure 5 and Figure 6 In the embodiment, the optical signal received from the transmitter is depicted as being transmitted via the second input path 34 i2 enters or is introduced into the prism and traces the local oscillator light as passing through the first optical path 34 i1 Entering or being introduced into the prism 34. It should be appreciated that although the optical signal is introduced into the second input path 34 i2 may be desirable, but other configurations may be used if the reduced number reduces losses through prism 34.

[0052] In various embodiments, the local oscillator light input to the prism can be oriented at an angle of about 45 degrees relative to the major axis of the polarization beam splitter surface of the prism 34 to allow the LO light to be split about 50 / 50 between the two polarization states. The LO light is combined with the optical signal in the prism 34, and the combined LO-optical signal is split into two orthogonally polarized light beams, which are output via substantially parallel output paths that are also substantially perpendicular to the input paths and can be in the same plane as one of the input paths or in a plane parallel to one of the input paths.

[0053] The skilled person will appreciate that the LO light need not be linearly polarized. For example, circularly polarized or elliptically polarized LO light may be used. Similarly, if the LO light is provided to the prism 34 in two polarization states, the alignment of the LO light at the input end has been solved.

[0054] Although the polarization of the local oscillator can be controlled, the polarization of the optical signal is usually unknown or uncontrollable in operation. Therefore, according to the polarization of the optical signal input into the prism 34, the optical signal power will be distributed between the two polarization paths or branches (arms) accordingly. Therefore, the outputs of the two photoelectric converters 36 will change in the same way. When the polarization of the signal is fully aligned along one branch, the photoelectric converter 36 associated with the branch will have a high output centered on the offset frequency dF between the local oscillator and the optical signal frequency, and the other branch will have a zero output centered on dF. When the signal is evenly distributed between the two branches, the output of the photoelectric converter 36 centered on dF is equal. By combining these two polarization outputs, the overall system dependence of the polarization of the incoming signal is reduced.

[0055] In various embodiments, the optical-to-electrical converter 36 may be implemented as a photodiode (PD) including an APD, a flip-chip, etc. to convert the first combined optical signal and the second combined optical signal into the first electrical signal and the second electrical signal. In various embodiments, the PD 36 and the electrical processing unit 38 have associated operating bandwidths 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 10, the PD 36 bandwidth and the electrical processing unit 38 may be set to 1.5 to 2 times the bandwidth of the optical signal.

[0056] like FIG. 5A to FIG. 5CAs further shown, the electrical processing unit 38 may include a transimpedance amplifier (TIA) 52 to amplify the electrical signal from the PD 36 before it enters an envelope detector 54 and is passed to a clock and data recovery (CDR) circuit 56. The electrical assembly 50 may also include a TEC controller 58 for controlling the operation of the TEC 42, as well as a processor 60 (such as a microcontroller) and associated memory, communication interfaces, etc. (as known in the art) to monitor and control some or all functions in the assembly 50 and communicate with other components in the module and / or system 10. The various electrical components may be mounted on and connected via a printed circuit board or other substrate 62, as well as connected separately from the board 62.

[0057] Due to the optical processing of the local oscillator light and the optical signal in one plane from one direction and the electrical processing of the signal in a plane perpendicular to the optical processing plane and in one direction, the alignment of the optical components and the combination of the prism surfaces as described above enable the device of the present invention to achieve a very small form factor. In various embodiments, the optical processing and the electrical processing are performed in the same physical direction. The receiver 30 can be implemented together with the transmitter component to provide a transceiver, or can be implemented independently on a line card.

[0058] Although FIG. 5A to FIG. 5C The embodiment shows the CDR on board 56, but it will be appreciated that the CDR 56 could be implemented on another board since the signal has already been received and reconstructed by that time.

[0059] The foregoing disclosure provides examples, illustrations and descriptions of the present invention, but is not intended to exclude or limit these implementations to the precise forms disclosed. Modifications and variations may be made based on the above disclosure, or may be obtained from the practice of the implementation. These and other variations and modifications of the present invention are possible and expected, and the preceding description and appended claims are intended to cover such modifications and variations.

[0060] As used herein, the term components are intended to be broadly interpreted as hardware, firmware, and / or a combination of hardware and software. It is apparent that the system and / or method described herein can be implemented in different forms of hardware, firmware, or a combination of hardware and software. The actual dedicated control hardware or software code used to implement these systems and / or methods does not limit the implementation. Therefore, the operation and behavior of the system and / or method are described herein without reference to specific software codes--it should be understood that software and hardware can be designed to implement the system and / or method based on the description herein.

[0061] Various levels of photonic, electrical, and mechanical integration may be employed for the various elements of the system. Multiple functions may be integrated into one or more modules or line cards housed in one or more racks or chassis in the system 10.

[0062] Hardware processor modules can range from general-purpose processors and CPUs to field-programmable gate arrays (FPGAs) to application-specific integrated circuits (ASICs). Software modules (which execute on the hardware) can be expressed in a variety of software languages ​​(e.g., computer code), including: C, C++, Java, TM ,Javascript,Rust,Go,Scala,Ruby,Visual Basic TM , FORTRAN, Haskell, Erlang and / or other object-oriented, procedural or other programming languages ​​and development tools. Computer code may include microcode or microinstructions, machine instructions (such as those generated by a compiler), code used to generate Web services, and files containing high-level instructions that are executed by a computer using an interpreter and employing control signals, encrypted code, and compressed code.

[0063] Some implementations are described herein in conjunction with thresholds. As used herein, satisfying a threshold may refer to a value that is greater than a threshold, more than a threshold, above a threshold, greater than or equal to a threshold, less than a threshold, less than a threshold, below a threshold, less than or equal to a threshold, equal to a threshold, etc.

[0064] Certain user interfaces have been described herein and / or shown in the accompanying drawings. 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 the device, which provides a user interface for display. In some implementations, the user interface is configurable by the device and / or the user (e.g., the user may change the size of the user interface, the information provided via the user interface, the location of the information provided via the user interface, etc.). Additionally or alternatively, the user interface may be preconfigured to a standard configuration, a specific configuration based on the type of device on which the user interface is displayed, and / or a set of configurations based on the capabilities and / or specifications associated with the device on which the user interface is displayed.

[0065] Even though particular combinations of features are stated in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of possible implementations. In fact, many of these features may be combined in ways not specifically stated in the claims and / or disclosed in the specification. Although each of the dependent claims listed below may be directly dependent on only one claim, the disclosure of possible implementations includes the combination of each dependent claim with every other claim in the claim set.

[0066] Any element, action or instruction used herein should not be interpreted as critical or essential unless clearly described in this way. Moreover, as used herein, the articles "a and an" are intended to include one or more items and can be used interchangeably with "one or more". In addition, as used herein, the term "group / set" is intended to include one or more items and can be used interchangeably with "one or more". In the case of only one item, the term "one" or similar language is used. Moreover, as used herein, the term "has, have, having, etc." is intended to be an open-ended term. In addition, unless otherwise expressly stated, the phrase "based on" is intended to mean "based at least in part on".

Claims

1. An optical combiner, comprising: a free-space beam combining and polarization splitting prism for combining a first input optical signal with a second input optical signal into a combined optical signal, and splitting the combined optical signal into a first combined optical signal and a second combined optical signal having orthogonal polarizations, Wherein, the prism comprises: a first optical input end, the first optical input end receiving the first input optical signal, a second optical input end, the second optical input end receiving the second input optical signal, wherein the second optical input end is parallel to the first optical input end or is in a plane at least parallel to the first optical input end, a combiner that combines the first input optical signal and the second input optical signal into a combined optical signal, and A splitter, the splitter splits the combined optical signal into a first combined optical signal and a second combined optical signal with orthogonal polarizations, the splitting is performed in one of the following planes: a plane of the first optical input end and the second optical input end, and a parallel plane of the first optical input end and the second optical input end, and the splitter outputs the first combined optical signal and the second combined optical signal perpendicular to the plane of the input path.

2. The optical combiner according to claim 1, wherein: The prism reflecting one of the first input optical signal and the second input optical signal toward a combining surface that combines the first input optical signal and the second input optical signal into a combined optical beam, polarization splitting the combined beam into two orthogonally polarized beams, reflecting one of the orthogonally polarized beams at 90 degrees within the plane, and The two orthogonally polarized light beams are reflected out of the plane at 90 degrees so that the respective orthogonally polarized light beams are output from the prism via parallel light output paths.

3. The optical combiner according to claim 1, wherein: The prism comprises: a reflective surface A positioned to reflect one of the first input optical signal and the second input optical signal; a combining surface B, the combining surface B being positioned to combine one of the first input light signal and the second input light signal, the input light signal from the reflecting surface A, and one of the first input light signal and the second input light signal, the input light signal not reflected from the reflecting surface A, into a combined light beam; a polarization splitting surface C, wherein the polarization splitting surface C splits the combined light beam into two orthogonally polarized light beams; a reflective surface D positioned to reflect one of the orthogonally polarized beams at 90 degrees in a plane; and At least one reflective surface E positioned to reflect two orthogonally polarized light beams out of a plane at 90 degrees to output the respective orthogonally polarized light beams from the prism via parallel light output paths.

4. An optical receiver, comprising: An optical input end, the optical input end receiving an optical signal; at least one local oscillator providing local oscillator light at a local oscillator frequency; a free-space beam combining and polarization splitting prism for combining an optical signal with the local oscillator light and splitting the combined optical signal into a first combined optical signal and a second combined optical signal having orthogonal polarizations; Two photoelectric converters, the two photoelectric converters are used to convert the first combined optical signal and the second combined optical signal into a first electrical signal and a second electrical signal; as well as an electrical combiner, the electrical combiner combining the first electrical signal and the second electrical signal into an output electrical signal, in, local oscillator light enters the prism via a first optical input in an orientation such that the local oscillator light is split by the prism between orthogonal polarizations, The optical signal enters the prism via a second optical input end, the second optical input end is parallel to the first optical input end and is in a plane at least parallel to the first optical input end, The local oscillator light and the optical signal are combined and split into a first combined optical signal and a second combined optical signal in the same plane as the first optical input end and the second optical input end, and the first combined optical signal and the second combined optical signal are output from the prism perpendicular to the plane of the input path, and The optoelectronic converter and the electrical combiner are in a plane parallel to the plane of the input path.

5. The optical receiver according to claim 4, wherein The photoelectric converter is a photodiode, which converts the first combined optical signal and the second combined optical signal into a first electrical signal and a second electrical signal; and The electrical combiner is a subtractor that combines the first electrical signal and the second electrical signal by subtraction.

6. The optical receiver according to claim 4, wherein: The local oscillator light is introduced into the first input path with a polarization that results in a 50 / 50 power split of the local oscillator light between the first combined optical signal and the second combined optical signal.

7. The optical receiver according to claim 4, further comprising: At least one output lens focuses each of the first combined light signal and the second combined light signal onto the optical-to-electrical converter.

8. The optical receiver according to claim 4, further comprising: An output lens is integrated with each of the first output path and the second output path on the prism to focus the first combined optical signal and the second combined optical signal onto the optical-to-electrical converter.

9. The optical receiver according to claim 4, further comprising: A beam collimator is provided to collimate the local oscillator light before the local oscillator light is introduced into the first input path of the prism.

10. The optical receiver according to claim 9, further comprising a lens that focuses the local oscillator light onto the beam collimator; and An optical isolator is positioned to prevent at least reflections from the beam collimator from entering the local oscillator laser.

11. The optical receiver according to claim 4, wherein: The first combined optical signal and the second combined optical signal are converted into electrical signals and combined into a combined electrical signal in a plane parallel to the plane of the first input path and the second input path.

12. The optical receiver according to claim 4, further comprising an optical subassembly including the at least one local oscillator; and An electrical subassembly, the electrical subassembly comprising the photoelectric converter and the electrical combiner, wherein: The optical subassembly is positioned at a 90 degree angle to the electrical subassembly.

13. The optical receiver according to claim 4, wherein: The optical signal is received from an optical transmitter, which transmits information via the optical signal.

14. A method for combining and splitting optical signals, the method comprising the following steps: providing a free-space beam combining and polarization splitting prism for combining a first optical signal with a second optical signal and splitting the combined optical signal into a first combined optical signal and a second combined optical signal having orthogonal polarizations; introducing the first optical signal into the prism via a first optical input end; providing the second optical signal to the prism via a second optical input, the second optical input being parallel to the first optical input and being in an at least parallel plane to the first optical input; combining the first optical signal and the second optical signal into a combined optical signal via the prism in the same plane as the first optical input end and the second optical input end; splitting the combined optical signal into a first combined optical signal and a second combined optical signal having orthogonal polarizations via the prism in the same plane as the first optical input end and the second optical input end; as well as The first combined light signal and the second combined light signal are output from the prism in a plane perpendicular to an input path.

15. The method according to claim 14, wherein: The step of introducing includes introducing the first optical signal into a first input path at a polarization that, after polarization splitting by the prism, results in a 50 / 50 power split of the first optical signal between the first combined optical signal and the second combined optical signal.

16. The method according to claim 14, wherein: The step of combining includes reflecting one of the first light signal and the second light signal via the prism toward a combining surface, the combining surface combining the first light signal and the second light signal into a combined light beam; and The output steps include: reflecting one of the first combined optical signal and the second combined optical signal at 90 degrees in a plane; as well as The first combined light signal and the second combined light signal are reflected out of a plane at 90 degrees to output the first combined light signal and the second combined light signal from the prism via parallel light output paths.

17. The method according to claim 14, wherein: The first optical signal is transmitted from a local oscillator at the first optical input with a known polarization.

18. The method according to claim 14, further comprising: The first optical signal is collimated prior to introducing the first optical signal.

19. The method according to claim 14, further comprising: The first optical signal and the second optical signal output through an output path are focused through a lens.

20. The method according to claim 14, wherein: The steps of combining, splitting and outputting include: reflecting one of the first light signal and the second light signal via a reflective surface A; combining, via a combining surface B, the light signal from the reflecting surface A among the first light signal and the second light signal and the light signal not reflected from the reflecting surface A among the first light signal and the second light signal into a combined light beam; Splitting the combined light beam into a first combined light signal and a second combined light signal with orthogonal polarizations via a polarization splitting surface C; reflecting one of the first combined optical signal and the second combined optical signal at 90 degrees in a plane via a reflective surface D; and Both the first combined light signal and the second combined light signal are reflected out of a plane at 90 degrees via at least one reflective surface E to output the first combined light signal and the second combined light signal from the prism via parallel light output paths.

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