Optical signal multiplexing and demultiplexing method and device for suppressing four-wave mixing effect

Abstract

Disclosed are an optical multiplexer (100, 100 ', 200, 200'), an optical demultiplexer, an optical transmitter comprising the optical multiplexer (100, 100 ', 200, 200'), an optical module comprising the optical transmitter and the optical demultiplexer, and methods of using the same. An optical multiplexer (100, 100 ', 200, 200') includes first and second beam combiners (110, 120), a polarized beam combiner (130), and an optical isolator (140). The first and second beam combiners (110, 120) each comprise a reflective surface and at least one optical filter for combining individual optical signals having the same polarization state into a multi-channel polarized optical signal. However, the two independent multi-channel polarized light signals have different polarization states. The polarized light beam combiner (130) comprises one or more reflecting surfaces and one or more polarization filters, and is used for combining the multi-channel polarized light signals into multi-channel output signals. The structure of the optical demultiplexer is similar to that of the optical multiplexer (100, 100 ', 200, 200'), but provides complementary or opposite functions. According to the multiplexer and the demultiplexer, the four-wave mixing effect is reduced.

Description

Technical Field

[0001] This invention relates to the field of optical communications, and in particular to optical multiplexers and demultiplexers, optical or photoelectric transmitters, receivers and transceivers including the same, and methods of manufacturing and using them. Background Technology

[0002] In optical communication, optical signals carry information. For example, a transmitter (e.g., a laser or laser diode) in an optical or optoelectronic transceiver converts one or more electrical signals into optical signals, and a receiver (e.g., a photodiode) in an optical or optoelectronic transceiver converts one or more optical signals back into electrical signals. One of the goals of optical communication research and development is to increase and / or maximize bandwidth (e.g., the amount of information transmitted) as much as possible.

[0003] At a given baud rate, the capacity of the transmitter or receiver in an optical transceiver is limited by the number of optical channels (or the number of wavelengths in a wavelength division multiplexing [WDM] system) that a transmitter optical subassembly (TOSA) or receiver optical subassembly (ROSA) can contain. When multiplexing and / or demultiplexing multichannel optical signals using conventional optical components, the primary concerns for the system in processing such signals are minimum size (e.g., compactness) and reliability.

[0004] In WDM systems, the most direct way to increase system transmission capacity is to reduce the spacing between multiplexed channels. Techniques for doing so include, for example, fine wavelength division multiplexing (e.g., LWDM or nLWDM), dense WDM (DWDM), etc. However, increased power and reduced channel spacing exacerbate four-wave mixing (FWM) effects between channels, especially in some fibers with low dispersion and high nonlinearity. Four-wave mixing refers to the interaction between two or three optical waves to generate one or more new optical waves at frequencies different from those of the channels in the WDM system. This phenomenon can lead to signal energy loss and may cause signal distortion.

[0005] When the channel spacing is relatively small, phase matching conditions are easier to satisfy, and a significant amount of power may be converted into new optical fields through four-wave mixing (e.g., different wavelengths / frequency, different beam shapes, and / or different propagation characteristics / properties). With equal channel spacing, the new frequency noise generated by FWM will directly coincide with the signal frequency in at least one channel, making crosstalk a more serious problem. The intensity of four-wave mixing is affected by incident power, fiber nonlinear parameters, zero-dispersion shift point, and polarization mode dispersion.

[0006] This "Background Art Discussion" section is for informational purposes only. The statements in this "Background Art Discussion" section do not constitute an admission that the subject matter disclosed in this "Background Art Discussion" section constitutes prior art to this disclosure, and no part of this "Background Art Discussion" section should be used as an admission that any part of this application (including this "Background Art Discussion" section) constitutes prior art to this disclosure. Summary of the Invention

[0007] Among the methods available for suppressing Four-Wave Mixing (FWM), polarization multiplexing is relatively easy to implement. The principle is that the efficiency of FWM is proportional to the scalar product of the polarization vectors of the mixed light waves; therefore, the FWM effect is minimized when the light waves in each channel of a WDM system are orthogonally polarized (e.g., S-polarized or P-polarized). This invention therefore relates to an apparatus and method that implements an optical path in a manner that suppresses four-wave mixing effects according to this principle.

[0008] This invention aims to overcome one or more deficiencies in the prior art and provides an optical multiplexer including a first beam combiner, a second beam combiner, and a polarization beam combiner. The first beam combiner includes a first reflective surface and a first filter, and is configured to combine first and second optical signals into a first multi-channel polarization optical signal. The first optical signal has a first polarization state and a first wavelength, and the second optical signal has the first polarization state and a second wavelength. The first filter reflects the first optical signal and allows the second optical signal to pass through. The second beam combiner includes a second reflective surface and a second filter, and is configured to combine third and fourth optical signals into a second multi-channel polarization optical signal. The third optical signal has a second polarization state and a third wavelength, and the fourth optical signal has the second polarization state and a fourth wavelength. The second filter reflects the third optical signal and allows the fourth optical signal to pass through. The polarization beam combiner includes a third reflective surface and a polarization filter, and is configured to combine the first and second multi-channel polarization optical signals into a multi-channel output signal. The polarization filter includes a polarization state-dependent filter configured to reflect the first multi-channel polarized optical signal and allow the second multi-channel polarized optical signal to pass through, and the third reflective surface includes a first non-selective mirror configured to reflect the first multi-channel polarized optical signal toward the polarization state-dependent filter.

[0009] In this optical multiplexer, all optical signals have different wavelengths. For example, each of the optical signals may have a wavelength that differs from that of an adjacent optical signal by at least 0.4 nm, at least 1 nm, at least 2 nm, or any other value ≥ 0.4 nm.

[0010] In a further embodiment, the optical multiplexer further includes one or more optical isolators located in the optical path of at least one of the first multi-channel polarized optical signal, the second multi-channel polarized optical signal, and the multi-channel output signal. The optical isolators are configured to isolate reflected light from the multi-channel signals passing through them. In other or even further embodiments, the first beam combiner further includes a first anti-reflective sheet or plate located on the same side of the first beam combiner as the first filter, and the second beam combiner further includes a second anti-reflective sheet or plate located on the same side of the second beam combiner as the second filter.

[0011] In various embodiments, the first beam combiner includes a first parallelepiped-shaped block, and the second beam combiner includes a second parallelepiped-shaped block. In such embodiments, the first reflecting surface and the first filter may be located on opposite sides of the first parallelepiped-shaped block, and the second reflecting surface and the second filter may be located on opposite sides of the second parallelepiped-shaped block. In some embodiments, the polarization beam combiner includes a third parallelepiped-shaped block. In such embodiments, the first non-selective mirror may be located on a first surface of the third parallelepiped-shaped block, and the polarization state-dependent filter may be located on a second surface of the third parallelepiped-shaped block parallel to the first surface of the third parallelepiped-shaped block.

[0012] In some embodiments, the optical multiplexer may further include first and second half-wave plates, which are respectively configured to (i) change the initial polarization state of the first and second optical signals to the first polarization state or (ii) change the initial polarization state of the third and fourth optical signals to the second polarization state. For example, if all the first to fourth optical signals have the same polarization state (e.g., S or P) when generated, the polarization state of half of the optical signals must be changed to make polarization multiplexing (e.g., using orthogonally polarized signals) effective.

[0013] This optical multiplexer can be scaled to larger systems with a greater number of channels. For example, the first beam combiner may further include a third filter and a fourth filter, and is further configured to combine a fifth and a sixth optical signal with the first and second optical signals to form the first multi-channel polarized optical signal. In this case, the fifth optical signal has the first polarization state and a fifth wavelength, and the sixth optical signal has the first polarization state and a sixth wavelength. The third filter can reflect the first and second optical signals and allow the fifth optical signal to pass through, and the fourth filter can reflect the first, second, and fifth optical signals and allow the sixth optical signal to pass through. Furthermore, the second beam combiner may further include a fifth filter and a sixth filter, and is further configured to combine a seventh and an eighth optical signal with the third and fourth optical signals to form the second multi-channel polarized optical signal. The seventh optical signal has the second polarization state and a seventh wavelength, and the eighth optical signal has the second polarization state and an eighth wavelength. The fifth filter can reflect the third and fourth optical signals and allow the seventh optical signal to pass through, and the sixth filter can reflect the third, fourth, and seventh optical signals and allow the eighth optical signal to pass through.

[0014] In an optical multiplexer with a larger number of channels, the first reflective surface may be located on the first side of the first beam combiner (e.g., the first parallelepiped block) closest to the polarization beam combiner, and the first, third, and fourth filters may be located on the second side of the first beam combiner (e.g., the first parallelepiped block) furthest from the polarization beam combiner. Similarly, the second reflective surface may be located on the first side of the second beam combiner (e.g., the second parallelepiped block) closest to the polarization beam combiner, and the second, fifth, and sixth filters may be located on the second side of the second beam combiner (e.g., the second parallelepiped block) furthest from the polarization beam combiner.

[0015] A further embodiment of the optical multiplexer with a larger number of channels may further include first, second, third, and fourth half-wave plates, which are respectively configured to change the initial polarization state of the first, second, fifth, and sixth optical signals to the first polarization state or (ii) change the initial polarization state of the third, fourth, seventh, and eighth optical signals to the second polarization state.

[0016] The present invention also relates to an optical transmitter comprising: this optical multiplexer; a plurality of light sources (e.g., optical or photoelectric emitters, such as laser diodes) configured to provide first, second, third, and fourth optical signals; a plurality of lenses, (i) through which the first and second optical signals pass before entering a first beam combiner, and (ii) through which the third and fourth optical signals pass before entering a second beam combiner; and a package or housing comprising the optical multiplexer, the light sources, and the lenses. The optical transmitter may further include an optical fiber adapter or connector configured to receive an optical fiber, in which case the optical fiber typically receives the multichannel output signals from the optical multiplexer; and / or first and second half-wave plates, the first and second half-wave plates being respectively configured to change (i) the initial polarization state of the first and second optical signals to the first polarization state or (ii) the initial polarization state of the third and fourth optical signals to the second polarization state. In the latter case, each of the plurality of light sources may be located on a single substrate, thus emitting light with the same polarization state.

[0017] Another aspect of the present invention relates to an optical transceiver, comprising the optical transmitter, an optical demultiplexer configured to separate an incoming multichannel optical signal into first, second, third, and fourth received optical signals, and a plurality of photodetectors configured to convert the first, second, third, and fourth received optical signals into first, second, third, and fourth received electrical signals. The first received optical signal may have a first polarization state and a first wavelength; the second received optical signal may have the first polarization state and a second wavelength; the third received optical signal may have the second polarization state and the third wavelength; and the fourth multichannel polarized optical signal may have the second polarization state and the fourth wavelength.

[0018] In some embodiments of the optical transceiver, the optical demultiplexer may include a polarization beam splitter, a first beam splitter, and a second beam splitter. The polarization beam splitter may include a polarization filter and a first reflective surface, and is configured to separate a multi-channel optical input signal into first and second multi-channel polarized optical signals. The first beam splitter may include a second reflective surface and a first filter, and is configured to separate the first multi-channel polarized optical signal into first and second optical signals. The first optical signal may have a first polarization state and a first wavelength, and the second optical signal may have the first polarization state and a second wavelength. The second beam splitter may include a third reflective surface and a second filter, and is configured to separate the second multi-channel polarized optical signal into third and fourth optical signals. The third optical signal may have a second polarization state and a third wavelength, and the fourth optical signal may have the second polarization state and a fourth wavelength.

[0019] In other or further embodiments, the optical transceiver may further include a plurality of laser drivers configured to transmit data drive signals to the plurality of light sources; a plurality of amplifiers configured to amplify the first, second, third, and fourth received electrical signals; an electrical interface configured to receive data signals corresponding to the data drive signals from an external device and provide the amplified first, second, third, and fourth received electrical signals to the external device; and a microprocessor or microcontroller configured to control the laser drivers and the amplifiers and to receive instructions and configuration information through the electrical interface. The optical transceiver may further include a bias control circuit configured to apply a bias voltage to the light source (e.g., a laser diode); a temperature control circuit or loop configured to adjust the temperature of the light source; and a monitoring photodiode configured to determine the signal strength of the optical signal. The microprocessor or microcontroller may be further configured to control these additional components in the optical transceiver.

[0020] Another aspect of the present invention relates to an optical demultiplexer, comprising a polarization beam splitter, a first beam splitter, and a second beam splitter. The polarization beam splitter includes a polarization filter and a first reflective surface. The polarization beam splitter is configured to separate a multi-channel optical input signal into first and second multi-channel polarized optical signals. The first beam splitter includes a second reflective surface and a first filter, and is configured to separate the first multi-channel polarized optical signal into first and second optical signals. The first optical signal has a first polarization state and a first wavelength, and the second optical signal has the first polarization state and a second wavelength. The second beam splitter includes a third reflective surface and a second filter, and is configured to separate the second multi-channel polarized optical signal into third and fourth optical signals. The third optical signal has a second polarization state and a third wavelength, and the fourth optical signal has the second polarization state and a fourth wavelength.

[0021] In various embodiments of the optical demultiplexer, the polarization filter may include a polarization state-dependent filter configured to reflect the first multi-channel polarized optical signal and allow the second multi-channel polarized optical signal to pass through; the first reflective surface may include a first non-selective reflective surface configured to reflect the first multi-channel polarized optical signal toward the first beam splitter; the second reflective surface may be located on the side of the first beam splitter closest to the polarization beam splitter; the first filter may be located on the side of the first beam splitter furthest from the polarization beam splitter; the third reflective surface may be located on the side of the second beam splitter closest to the polarization beam splitter; and the second filter may be located on the side of the second beam splitter furthest from the polarization beam splitter.

[0022] In addition to polarization multiplexing and orthogonal polarization of the optical signals in each channel, this optical multiplexer and demultiplexer can also employ unequal channel spacing, phase conjugation, dispersion management, and other methods to suppress FWM. These and other advantages of the invention will become apparent from the following detailed description of various embodiments. Attached Figure Description

[0023] Figure 1 This is a block diagram illustrating an exemplary four-signal embodiment of an optical multiplexer according to the present invention.

[0024] Figure 2 This is a block diagram illustrating an alternative four-signal optical multiplexer according to the present invention.

[0025] Figure 3 This is a block diagram illustrating an exemplary eight-signal optical multiplexer according to the present invention.

[0026] Figure 4 This is a block diagram illustrating one or more alternative eight-signal optical multiplexers according to the present invention.

[0027] Figure 5 This is an illustration of an exemplary optical emitter according to one or more embodiments of the present invention.

[0028] Figure 6 This is an illustration of an exemplary optical demultiplexer according to one or more embodiments of the present invention.

[0029] Figure 7 This is an illustration of components in an exemplary optoelectronic transceiver and / or module according to an embodiment of the present invention. Detailed Implementation

[0030] Reference will now be made in detail to various embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the following embodiments, it should be understood that these descriptions are not intended to limit the invention to these embodiments. Rather, the invention is intended to cover alternatives, modifications, and equivalents that may fall within the spirit and scope of the invention as defined by the appended claims. Furthermore, numerous specific details are set forth in the following detailed description of the invention to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of this disclosure.

[0031] Certain portions of the following detailed description are presented in the form of processes, procedures, logic, functions, and other symbolic representations of operations on signals, codes, data bits, or data streams within a computer, transceiver, processor, controller, and / or memory. These descriptions and representations are commonly used by those skilled in the art of data processing to effectively communicate the substance of their work to others skilled in the art. Processes, procedures, logical operations, functions, etc., are generally considered here as steps or self-consistent sequences of steps or instructions that lead to desired and / or anticipated results. These steps generally involve the physical manipulation of physical quantities. Typically, though not always, these quantities take the form of electrical, magnetic, optical, or quantum signals capable of being stored, transmitted, combined, compared, and / or manipulated otherwise in a computer, data processing system, optical component, or circuit. Sometimes, it proves convenient to refer to these signals as bits, streams, values, elements, symbols, characters, terms, numbers, information, or the like, primarily due to common usage. However, it should be remembered that all these and similar terms are associated with appropriate physical quantities and / or signals and are merely convenient labels applied to these quantities and / or signals.

[0032] Unless otherwise specifically stated or apparent from the following discussion, in this application, the use of terms such as “processing,” “operation,” “computation,” “determining,” or similar terms refers to the actions and processes of a computer, data processing system, or similar processing device (e.g., an electrical, optical, or quantum computing or processing device or circuit) that manipulate and convert data represented as physical (e.g., electronic) quantities. These terms also refer to the actions and processes of processing devices that manipulate or convert physical quantities within components of a circuit, system, or architecture (e.g., registers, memories, other such information storage, transmission, or display devices, etc.) into other data or information similarly represented within other components of the same or different systems or architectures.

[0033] Furthermore, in the context of this application, unless otherwise indicated from the context of its use, it should be understood that the terms "signal" and "optical signal" refer to any known structure, construction, arrangement, technique, method, and / or process for physically transmitting data or information from one point to another. The term "wavelength" can refer to the center wavelength of light in a wavelength band that can be relatively narrow and generally does not significantly overlap with light having different wavelengths (i.e., the center wavelength in different wavelength bands). Moreover, unless otherwise indicated from the context of its use, the terms "fixed," "given," "certain," and "predetermined" generally refer to theoretically variable values, quantities, parameters, constraints, conditions, states, processes, procedures, methods, practices, or combinations thereof, but are usually predetermined and do not change during use. Similarly, for convenience and brevity, the terms "time," "rate," "period," and "frequency" are generally interchangeable and can be used interchangeably herein, as are the terms "data," "bit," and "information," but these terms generally have their meanings generally accepted in the art. For convenience and brevity, the terms “optical” and “optoelectronic” are generally used interchangeably throughout this document, and the use of either term also includes the other unless the context clearly indicates otherwise, but these terms generally have their meanings accepted in the art. Furthermore, the term “transceiver” refers to a device having at least one receiver and at least one transmitter, and the use of the term “transceiver” also includes the individual terms “receiver” and / or “transmitter”, unless the context clearly indicates otherwise. Moreover, for convenience and brevity, the terms “connected to,” “coupled to,” “communicating with,” and their grammatical variations (these terms also refer to direct and / or indirect relationships between connected, coupled, and / or communicating elements, unless the context of the term’s use clearly indicates otherwise) are used interchangeably, but these terms also generally have their meanings accepted in the art.

[0034] The various embodiments and / or examples disclosed herein can be combined with other embodiments and / or examples, provided that such combination is not expressly disclosed herein as disadvantageous, undesirable, or detrimental. The invention, in its various aspects, will be explained in more detail below with reference to exemplary embodiments.

[0035] Exemplary optical multiplexer

[0036] Figure 1 An exemplary optical multiplexer 100 is shown, comprising a first beam combiner 110, a second beam combiner 120, a polarization beam combiner 130, and an optical isolator 140. The first beam combiner 110 combines first and fourth optical (light) signals 101 and 104, each having a first and a fourth wavelength and signal strength, respectively, to output a first combined signal 105. The second beam combiner 120 combines second and third optical signals 102 and 103, each having a second and a third wavelength and signal strength, respectively, to output a second combined signal 106. The first and fourth optical signals 101 and 104 (and thus the first combined signal 105) have one of two polarization types (e.g., S or P), and the second and third optical signals 102 and 103 (and thus the second combined signal 106) have the other of the two polarization types.

[0037] An exemplary multiplexer 100 implements a polarization beam combining method. Beams or signals having the same polarization state are combined through a set of filters (e.g., those on or in a first beam combiner 110), and beams or signals having a polarization state different from those combined by the first set of filters but the same as each other are combined through another set of filters (e.g., those on or in a second beam combiner 120). Combined beams or signals with different polarization states are combined by reverse polarization beam splitting (PBS), thereby achieving polarization multiplexing.

[0038] by Figure 1Taking a four-channel system 100 as an example, the channel order is CH1 (signal 101), CH2 (signal 102), CH3 (signal 103), and CH4 (signal 104). CH1 may have the smallest wavelength, and the wavelengths of CH2, CH3, and CH4 increase sequentially, in some embodiments by a constant or substantially constant increment or amount (e.g., 1.2–3.5 nm, depending on the applicable optical communication standard or protocol). Typically, there are two polarization states (e.g., S or vertical polarization, and P or horizontal polarization). To suppress four-wave mixing, the polarization states of the four channels should allow two channels with P or horizontal polarization to be shared by one channel with S or vertical polarization (or vice versa; i.e., two channels with S or vertical polarization are shared by one channel with P or horizontal polarization). In other words, when the signals are arranged in wavelength order, no signal is adjacent only to a signal with the same polarization state. Therefore, for example, the four channels may have SPPS or PSSP polarization states in wavelength order. Alternatively, the four channels may have SPSP or PSPS polarization states in wavelength order, but not SSPP or PPSS polarization states. An exemplary multiplexer 100 achieves polarization multiplexing by combining the first and fourth channels CH1 and CH4, which have the same polarization state (e.g., S), through a first set of filters (e.g., those on or in the first beam combiner 110), combining the second and third channels CH2 and CH3, which have the same polarization state (e.g., P), through another set of filters (e.g., those on or in the second beam combiner 120), and then using a reverse PBS to combine the optical signals with two vertical polarization states.

[0039] Polarizing beam combiner 130 combines the first and second combined signals 105 and 106 to form a four-wave output signal 107. Isolator 140 isolates reflected light from the output signal 107 from downstream devices, thereby reducing the effect of such reflected light on the light source (e.g., an emitter, such as a light-emitting diode or laser; not shown). Both polarizing beam combiner 130 and isolator 140 are angled relative to the incoming light signal to minimize or avoid rearward reflection of the incoming light signal toward the light source.

[0040] The first and second beam combiners 110 and 120 comprise blocks of material (e.g., glass) that are substantially transparent at the wavelengths of the respective optical signals 101 and 104 or 102 and 103. Each of the first and second beam combiners 110 and 120 may include corresponding coatings or surfaces 116 and 126 (e.g., mirrors) that completely reflect the first and third optical signals 101 and 103. Alternatively, the first and third optical signals 101 and 103 may be reflected by the interface between the first and second beam combiners 110 and 120 and an external medium (e.g., air or an inert gas). In a further alternative, the first and second beam combiners 110 and 120 may comprise a frame having a parallelepiped shape, wherein two or four faces may be square or rectangular, having a hollow or unfilled internal space through which the optical signals are transmitted. Individual plates or blocks 116 and 126 having reflective surfaces facing the interior space of the respective first or second beam combiner 110 or 120 can be fixed to the frame (e.g., using adhesive).

[0041] The first beam combiner 110 has a first antireflective (AR) sheet or plate 112 fixed thereon. The first antireflective sheet or plate is substantially transparent at the wavelength of the first optical signal 101 but is configured to minimize reflection of the first optical signal 101 backward toward a light source (not shown). In some embodiments, the first AR sheet or plate 112 comprises an AR coating on glass or another transparent medium (e.g., polycarbonate) and may further comprise a filter coating (e.g., a functional film that allows the first optical signal 101 to pass through but substantially blocks light with different polarizations or wavelengths differing from the first optical signal 101 by x nm or greater, where x is 2, 3, 4, 5, or greater). The filter coating may be located on the first AR sheet or plate 112 or, when the first beam combiner 110 is a solid material block, on the surface of the first beam combiner 110. The first beam combiner 110 also has a first filter 114 thereon. The first AR sheet or plate 112 and the first filter 114 may be fixed to the first beam combiner 110, for example, using an adhesive. One of the surfaces of the first filter 114 and the first beam combiner 110 that contacts the other is coated with a second functional film 118. This second functional film reflects the first optical signal 101 and transmits the fourth optical signal 104. The second functional film 118 may have wavelength-dependent transmission and reflection characteristics similar to those of the filter coating on the first AR sheet or plate 112, but for a different wavelength. The fourth optical signal 104 is refracted, and the first optical signal 101 is reflected by the second functional film 118 at the same angle. Therefore, the second functional film 118 functions as a beam combining surface in the first beam combiner 110. The surface of the first beam combiner 110 through which the first combined signal 105 passes may be coated with a first AR film.

[0042] The second beam combiner 120 may be substantially similar to or identical to the first beam combiner 110, except that it is configured to combine the second and third optical signals 102 and 103, which have wavelengths and polarization types different from the first and fourth optical signals 101 and 104. Therefore, the second beam combiner 120 has a second antireflective (AR) sheet or plate 122 fixed thereon, which is substantially transparent at the wavelength of the third optical signal 103 but configured to minimize rearward reflection of the third optical signal 103 toward a corresponding light source (not shown). The second beam combiner 120 also has a second filter 124 thereon. One of the surfaces of the second filter 124 and the second beam combiner 120 that contacts the other is coated with a third functional film 128, which reflects the third optical signal 103 and transmits the second optical signal 102. The third optical signal 103 is reflected, and the second optical signal 102 is refracted by the third functional film 128 at the same angle. Therefore, the third functional film 128 functions as a beam combining surface in the second beam combiner 120. The surface of the second beam combiner 120 through which the second combined signal 106 passes can be coated with a second AR film.

[0043] In the optical signals 101-104 of the exemplary four-channel system, the first optical signal 101 and the fourth optical signal 104 have the same polarization state (e.g., S), the second optical signal 102 and the third optical signal 103 have the same polarization state (e.g., P), and the polarization directions of the first combined signal 105 and the second combined signal 106 are perpendicular. The polarization state of the optical signals 101-104 can be achieved by polarization (e.g., passing the signal through a polarizer, not shown) or by directly controlling the output of the laser emitting the optical signals.

[0044] The polarizing beam combiner 130 includes a reflector block 132, a transmission block or space 134 having a parallelepiped shape, wherein two or four faces may be square or rectangular (similar to the first and second beam combiners 110 and 120), and a filter block 136. In some embodiments, one or both of the surfaces of the reflector block 132 and the transmission block or space 134 that are in contact with each other reflect the incident light of the first combined optical signal 105. Alternatively, the transmission block or space 134 may include a frame with sidewall openings (e.g., for the passage of optical signals) and an open interior space. In this case, the surface of the reflector block 132 facing the interior of the transmission block or space 134 can completely reflect the first combined optical signal 105.

[0045] In some embodiments, one or both of the surfaces in contact with each other in the transmission block or space 134 and the filter block 136 include polarization-dependent films that reflect light (e.g., S) having the same polarization state as the first combined optical signal 105 and transmit light (e.g., P) having the same polarization state as the second optical signal 106. The polarization-dependent films at the interface between the transmission block or space 134 and the filter block 136 combine the first and second combined optical signals 105 and 106 by polarization multiplexing, resulting in the formation of a four-channel optical signal 107 (each with its own polarization state SPPS).

[0046] Figure 2 The image shows an alternative optical multiplexer 100'. The multiplexer 100' includes a first beam combiner 110, a second beam combiner 120, and the polarized beam combiner 130, and... Figure 1 The optical multiplexer 100 is similar to or the same as the optical multiplexer 100. Therefore, the same reference numerals in different figures indicate the same or substantially the same structure. However, Figure 1 The optical isolator 140 is replaced by first and second optical isolators 142 and 144. The first optical isolator 142 is located between the first beam combiner 110 and the polarizing beam combiner 130, and the second optical isolator 144 is located between the second beam combiner 120 and the polarizing beam combiner 130. Each of the surfaces of the first and second optical isolators 142 and 144 facing the first and second beam combiners 110 and 120, respectively, may have an AR coating thereon as a supplement or replacement for the AR coating (one or more) on the polarizing beam combiner 130.

[0047] Figure 3An alternative eight-channel optical multiplexer 200 is shown, including a first beam combiner 210, a second beam combiner 220, a polarization beam combiner 230, and an optical isolator 240. The first beam combiner 210 combines first, fourth, fifth, and eighth optical (light) signals 201, 204, 205, and 208, respectively, having first, fourth, fifth, and eighth wavelengths and signal strengths, to output a first combined polarization signal 215. The second beam combiner 220 combines second, third, sixth, and seventh optical signals 202, 203, 206, and 207, respectively, having second, third, sixth, and seventh wavelengths and signal strengths, to output a second combined polarization signal 225. The first, fourth, fifth, and eighth optical signals 201, 204, 205, and 208 (and thus the first combined polarization signal 215) have one of two polarization types (e.g., S or P), and the second, third, sixth, and seventh optical signals 202, 203, 206, and 207 (and thus the second combined polarization signal 225) have the other of the two polarization types.

[0048] The wavelengths of the optical signals 201-208 can increase or decrease sequentially. For example, the first optical signal 201 may have the shortest wavelength, in which case the eighth optical signal 208 has the longest wavelength, and the second to seventh optical signals 202-207 have successively increasing wavelengths, greater than the wavelength of the first optical signal 201 but less than the wavelength of the eighth optical signal 208. Alternatively, the first optical signal 201 may have the longest wavelength, in which case the eighth optical signal 208 has the shortest wavelength, and the second to seventh optical signals 202-207 have successively decreasing wavelengths, less than the wavelength of the first optical signal 201 but greater than the wavelength of the eighth optical signal 208.

[0049] Figure 3 The optical multiplexer 200 in the middle has the same characteristics as... Figure 1-2 The multiplexers 100 and 100' in this paper have essentially the same advantages because they suppress four-wave mixing by arranging eight channels so that signal pairs with P or horizontal polarization are shared by a channel with S or vertical polarization. In the arrangement described above, the wavelengths and polarization types of the eight optical signals 201-208 in the respective channels are described in Table 1 below.

[0050] Table 1

[0051]

[0052] Where δ is the difference between the wavelengths of the first and second channels (and δ may increase slightly as the channel number increases [typically no more than 5-10%]), X is one of two polarization types (e.g., S or P), and Y is the other of the two polarization types.

[0053] Each of the first and second beam combiners 210 and 220 may include AR sheets or plates 252 and 262 thereon. The AR sheets or plates 252 and 262 are similar to... Figure 1-2 AR sheets or plates 112 and 122 in the middle. The first beam combiner 210 ( Figure 3 The second beam combiner 220 also includes a coating or surface 212 that completely reflects the first optical signal 201, the first combined signal 211, and the second combined signal 213. The second beam combiner 220 also includes a similar coating or surface 222 that completely reflects the seventh optical signal 207, the third combined signal 221, and the fourth combined signal 223. The coatings or surfaces 212 and 222 are similar to... Figure 1-2 The coating or surface 116 and 126 in the middle.

[0054] return Figure 3 The first beam combiner 210 further includes a first filter 254, a second filter 256, a third filter 258, a first functional film 214, a second functional film 216, and a third functional film 218 thereon. The first functional film 214 reflects the first optical signal 201 and transmits the fourth optical signal 204. The fourth optical signal 204 is refracted, and the first optical signal 201 is reflected by the first functional film 214 at the same angle to form the first combined signal 211. Similarly, the second functional film 216 reflects the first combined signal 211 and refracts (transmits) the fifth optical signal 205 at the same angle to form the second combined signal 213, and the third functional film 218 reflects the second combined signal 213 and refracts (transmits) the eighth optical signal 208 at the same angle to form the first combined polarization signal 215. Therefore, the first, second, and third functional films 214, 216, and 218 function as beam combining surfaces in the first beam combiner 210.

[0055] The second beam combiner 220 may be substantially similar to or identical to the first beam combiner 210, except that it is configured to combine the second, third, sixth, and seventh optical signals 202, 203, 206, and 207, which have wavelengths and polarization types different from the first, fourth, fifth, and eighth optical signals 201, 204, 205, and 208. Therefore, the second beam combiner 220 has a second AR sheet or plate 262, fourth, fifth, and sixth filters 264, 266, and 268 thereon, and fourth, fifth, and sixth functional films 224, 226, and 228. The fourth, fifth, and sixth functional films 224, 226, and 228 respectively (i) reflect the seventh optical signal 207 and transmit the sixth optical signal 206 to form a third combined optical signal 221, (ii) reflect the third combined optical signal 221 and transmit the third optical signal 203 to form a fourth combined optical signal 223, and (iii) reflect the fourth combined optical signal 223 and transmit the second optical signal 202 to form the second combined polarized optical signal 225. Therefore, the fourth, fifth, and sixth functional films 224, 226, and 228 function as beam combining surfaces in the second beam combiner 220.

[0056] Figure 3 The polarizing beam combiner 230 and the optical isolator 240 in the above-mentioned polarizing beam combiner 230 and the optical isolator 240 with Figure 1 The polarization beam combiner 130 and the optical isolator 140 described herein are the same or substantially the same. Therefore, this optical multiplexer is not limited to a four-channel system and can be extended to higher bandwidth applications where the number of channels is 4n or 2p, where n is an integer of 1 or greater and p is an integer of 2 or greater.

[0057] In the alternative arrangements described in Table 1 above, Figure 3 The wavelengths and polarization types of the eight optical signals 201-208 in the multiplexer 200 are described in Table 2 below.

[0058] Table 2

[0059]

[0060] Wherein δ, X, and Y are as described in Table 1. Those skilled in the art can readily deduce other permutations in which each of a signal pair having a first polarization type is shared by a signal having the other polarization type. In other words, a first signal pair having the first polarization type is shared by a first signal having the other polarization type, and a second signal pair having the first polarization type is shared by a second signal having the other polarization type. Similarly, a first signal pair having the second polarization type is shared by a first signal having the first polarization type, and a second signal pair having the second polarization type is shared by a second signal having the first polarization type. In some embodiments, the sharing condition for both polarization states is met (i.e., each of a signal pair having one polarization state is shared by a signal having the other polarization state, and the signal having the other polarization state is not shared with any other signal pair having the first polarization state).

[0061] Figure 4 An exemplary alternative eight-channel optical multiplexer 200' is shown according to an embodiment of the present invention. The optical multiplexer 200' is... Figure 3 The optical multiplexer 200 is essentially the same, but it further includes first to fourth half-wave plates 272, 274, 276, and 278. These half-wave plates 272, 274, 276, and 278 can convert S-polarized light to P-polarized light, or vice versa. This greatly simplifies the design and fabrication of light sources (e.g., laser diodes) that can produce light with the same polarization state, and therefore can be manufactured monolithically (e.g., on a single substrate). Figure 4 As shown, the half-wave plates 272, 274, 276, and 278 can be placed between the light source and the second beam combiner 220 (e.g., between the light source and the fifth and sixth filters 266 and 268, as shown), or directly on the AR sheet or plate and / or the filter (e.g., directly on the AR sheet or plate 262 and the fourth filter 264, as shown). The half-wave plates 272, 274, 276, and 278 can be fixed to the AR sheet or plate and / or the filter using adhesive.

[0062] Alternatively, when all light sources have the same polarization state, the half-wave plates 272, 274, 276, and 278 can be placed between the light source and the first beam combiner 210, or directly on the AR plate or board 252 and / or the first, second, and third filters 254, 256, and 258. In a further alternative, the optical multiplexer 200' may include a single half-wave plate located between (i) either the first beam combiner 210 or the second beam combiner 220 and (ii) the polarized beam combiner 230, substantially in relation to... Figure 2 The first and second optical isolators 142 and 144 are located at the same position.

[0063] Exemplary optical emitter

[0064] Figure 5 Showing includes Figure 3 An exemplary optical transmitter 300 is provided for an exemplary optical multiplexer 200. Furthermore, the optical transmitter 300 includes a light source 310 and a lens 320. Figure 3 All components of the optical transmitter 300 shown may be contained within a housing or package (not shown), and the multichannel output signal 245 may be focused through one or more additional lenses to a far-field point in an optical fiber (not shown). The optical fiber may be conventionally coupled and / or connected to the housing or package of the optical transmitter 300 using a ferrule or similar connector.

[0065] The light source 310 includes a first light source block 315x, which includes first to fourth light sources 311x-314x, and a second light source block 315y, which includes fifth to eighth light sources 311y-314y. Typically, the first to fourth light sources 311x-314x in the first light source block 315x are located on one substrate and emit light with a first polarization state, while the fifth to eighth light sources 311y-314y in the second light source block 315y are located on another substrate and emit light with a second polarization state. However, as per [the relevant regulations]... Figure 4 The light source 310 can be located entirely on a single substrate and emit light with the same polarization state, as long as the polarization state of the light from each of the light sources in one of the light source blocks 315x and 315y is changed (e.g., by passing through a half-wave plate).

[0066] Each of the first to eighth light sources 311x-314y typically includes a laser diode configured to emit light within a relatively narrow optical band (e.g., having a full width at half maximum (FWHM) ≤ 1 nm, or any value < 1 nm) to maximize the number of channels within the wavelength band allowed by the optical communication protocol or standard and minimize the crosstalk probability between channels. Each of the laser diodes may include a vertical-cavity surface-emitting laser (VCSEL) diode, although the invention is not limited to this type of laser source. For example, the light sources 311x-314x and 311y-314y may be or include a dual heterostructure laser, a quantum well laser, a quantum cascade laser, an interband cascade laser, a split-confined heterostructure laser, a distributed Bragg reflector laser, a distributed feedback laser, a vertical external cavity surface-emitting laser, or an external cavity diode laser.

[0067] The lens 320 is conventional and may include a spherical lens (e.g., as shown), a convex lens and / or a concave lens (e.g., biconvex, biconcave, plano-convex, plano-concave, or meniscus [positive or negative] lens), a hemispherical lens, a grating, a Fresnel lens, etc. Each of the lenses 321-328 focuses the corresponding optical signal to a focal point, typically on a reflective or refracting surface distal to the corresponding beam combiner 210 or 220. The transmitter 300 may include additional components in various optical paths, such as one or more additional lenses (e.g., in the optical paths of the first and second combined polarization signals 215 and 225, between the first and second beam combiners 210 and 220 and the polarization beam combiner 230, and / or in the optical path of the multi-channel output signal 245, upstream and / or downstream of the optical isolator 240) and / or one or more bandpass and / or polarization filters.

[0068] Exemplary optical demultiplexer

[0069] The principles behind this optical multiplexer also apply to optical demultiplexers. Figure 6 An exemplary optical demultiplexer 400 according to an embodiment of the present invention is shown, including a polarization beam splitter (PBS) 450, a first beam splitter 410, a second beam splitter 420, and a plurality of lenses 431-438. The beam splitter 450 may include a structural block comprising a mirror 452 and a polarization filter 454, similar to... Figure 1-3 The beam combiners 130 and 230 are located in the beam splitter. Therefore, the polarization filter 454 reflects any light having one of two polarization states (e.g., S or P) and refracts or allows light with the other polarization state to pass through. The mirror 452 is typically a total reflector that reflects light 419 having said one polarization state toward the input port of the first beam splitter 410.

[0070] The first beam splitter 410 includes a first plurality of filters 412, 414, 416, and 418 and a first mirror 460. The second beam splitter 420 includes a second plurality of filters 422, 424, 426, and 428 and a second mirror 465. The filters 412, 414, 416, 418, 422, 424, 426, and 428 in the multiplexer 400 are typically wavelength-selective filters and may include individual components adhered to or fixed to the surface of the first or second beam splitter 410 or 420, or a coating applied to the surface of the first or second beam splitter 410 or 420, similar to... Figure 3 The first and second beam combiners 210 and 220 are described in the text. The filters 412 and 422 are optional and may be or include high-bandpass filters and / or low-bandpass filters. The first and second mirrors 460 and 465 are non-selective or fully reflective mirrors and cover the areas or locations where at least the optical signals 401, 415, 417, 405, 425, and 427 strike, but do not cover the areas or locations where the incoming four-channel optical signals 419 and 429 strike (i.e., the input ports of the first and second beam splitters 410 and 420).

[0071] The demultiplexer 400 is similar to Figure 3 The operation of the multiplexer 200 is reversed. The 8-channel optical signal 455 is separated into first and second 4-channel optical signals 419 and 429 by a filter 454 in the beam splitter 450. The first 4-channel optical signal 419, having only one polarization type, is reflected by the filter 454, and the second 4-channel optical signal 429, having only the other polarization type, passes through the filter 454. The 4-channel optical signal 419 is then reflected by a mirror 452, which is typically a non-selective mirror (i.e., it reflects substantially all of the signal in the first 4-channel optical signal 419), but in some embodiments, it may include a polarization-dependent filter (i.e., it reflects light with one polarization type but allows light with the other polarization type to pass through).

[0072] In beam splitters 410 and 420, the four-channel optical signals 419 and 429 strike fourth and eighth filters 418 and 428, respectively. The fourth and eighth single-channel optical signals 404 and 408 pass through the fourth and eighth filters 418 and 428, but signals 417 and 427 are reflected by the fourth and eighth filters 418 and 428 towards mirrors 460 and 465, respectively. Signals 417 and 427 respectively comprise the remaining three channels of the four-channel optical signals 419 and 429. Mirrors 460 and 465 reflect signals 417 and 427 towards the third and seventh filters 416 and 426. The third and seventh optical signals 403 and 407 pass through the third and seventh filters 416 and 426, and signals 415 and 425 are reflected. Signals 415 and 425 respectively comprise the remaining two channels of the three-channel optical signals 417 and 427. Mirrors 460 and 465 reflect signals 415 and 425 toward the second and sixth filters 414 and 424. The first and fifth optical signals 401 and 405 are reflected by the second and sixth filters 414 and 424, but the second and sixth optical signals 402 and 406 pass through the second and sixth filters 414 and 424, respectively. The first and fifth optical signals 401 and 405 are reflected by mirrors 460 and 465 toward optional first and fifth filters 412 and 422, where they pass through.

[0073] The first to eighth optical signals 401-408 from the corresponding first to eighth filters 412, 414, 416, 418, 422, 424, 426, and 428 are focused and / or collimated by the first to eighth lenses 431-438 onto a corresponding first to eighth optical signal detector (e.g., a photodiode, not shown). The first to eighth optical signals 401-408 have different wavelengths. As described elsewhere herein, there is a spacing between adjacent wavelengths of the signals 401-408. Furthermore, the demultiplexer 400 may include additional components in various optical paths, such as one or more additional lenses, bandpass filters, and / or mirrors, as described herein, but in conjunction with... Figure 1-4 The optical multiplexers 100, 100', 200 and 200' described in the text are those opposite or complementary configurations.

[0074] Exemplary optical transceivers and / or optical modules

[0075] Figure 7This is an illustration of an exemplary optical transceiver and / or optical module 500 according to an embodiment of the present invention, including an electrical interface 510, one or more laser drivers 520, a transmitter optical subassembly (TOSA) 530, an optical multiplexer 540, a microprocessor or microcontroller (e.g., MCU) 550, an optical demultiplexer 560, a receiver optical subassembly (ROSA) 570, and a limiting amplifier 580, sequentially coupled, and temperature control circuitry 590. The TOSA 530 includes a plurality of laser diodes (LDs) 532, a corresponding plurality of modulators 534, and a corresponding plurality of monitoring photodiodes (MPDs) 536. The ROSA 570 typically includes a plurality of photodiodes (PDs) 572 configured to receive optical signals from a network (e.g., transmitted via fiber optic cable) and convert the optical signals into electrical signals, and optionally, one or more transimpedance amplifiers 574 configured to amplify the electrical signals. The limiting amplifier 580 is configured to amplify the signals received from the ROSA 570.

[0076] In the transmitter path of the optical transceiver and / or module 500, the laser driver 520 receives electrical data signals from the electrical interface 510 and sends data drive signals or pulses to the modulator 534. The electrical interface 510 can receive the data signals from a host device and is conventional. The LD 532 receives a bias signal or voltage from the bias control circuit 525. Alternatively, the LD 532 can receive the data drive signals or pulses directly from the laser driver 520, in which case the modulator 534 may not be necessary. The MPD 536 is connected to the MCU 550 via one or more analog-to-digital converter (ADC) circuits or modules 555. Therefore, the MCU 550 can receive digital signals (e.g., voltages) corresponding to the value of the feedback current from each MPD 536, which can be used for comparison with one or more thresholds or voltages representing the target and / or maximum operating range of the laser driver 520. The MPD 536, analog-to-digital converter 555, MCU 550, and laser driver 520 can form a closed-loop automatic power control (APC) regulation loop to maintain the target optical output power from the LD 532.

[0077] The TOSA 530 (i.e., the modulator 534 or the LD 532) outputs multiple optical signals, half of which have one of two polarization types and the other half have the other polarization type, as described herein. Figure 1-4The optical multiplexer 540 is used for combination. The multiplexer 540 includes first and second beam combiners 542 and 544, and a polarizing beam combiner 546, as described elsewhere herein. In a further embodiment, the multiplexer 540 may further include a plurality of lenses as described herein, and the first and second beam combiners 542 and 544 may include corresponding first and second plurality of filters and first and second mirrors, as described herein. The polarizing beam combiner 546 may include one or more mirrors and one or more polarizing filters, as described herein.

[0078] like Figure 7 As shown, each of the first and second beam combiners 542 and 544 combines four optical signals with the same polarization state to create a four-channel polarized optical signal. The two four-channel polarized optical signals are then combined by the polarization beam combiner 546 to form an eight-channel optical output signal. However, the first and second beam combiners 542 and 544 can combine different numbers of optical signals, and the polarization beam combiner 546 can output optical signals with different numbers of channels. Furthermore, the optical multiplexer 540 may further include one or more optical isolators and / or multiple half-wave plates as described herein.

[0079] In the receiver path of the optical transceiver and / or module 500, the optical demultiplexer 560 receives incoming multi-channel optical signals. Figure 6 Similar to the optical demultiplexer 400, the optical demultiplexer 560 includes a PBS 566 and first and second beam splitters 562 and 564. In a further embodiment, the demultiplexer 560 may further include... Figure 6 The plurality of lenses, and the first and second beam splitters 562 and 564 may include corresponding third and fourth plurality of filters and third and fourth mirrors, as per [reference to...]. Figure 6 The PBS 566 may include one or more mirrors and one or more polarization filters, as described above. Figure 6 The optical demultiplexer 400 described in the text.

[0080] like Figure 7 As shown, the eight-channel optical input signal is split into two four-channel optical signals with different polarization states by the PBS 566. Each four-channel polarized optical signal is then demultiplexed into a single optical signal by the first and second beam splitters 562 and 564, as described herein. However, the PBS 566 can receive optical signals with different numbers of channels, and the first and second beam splitters 562 and 564 can receive and demultiplex different numbers of optical signals.

[0081] The PD 572 receives the individual optical signals and converts them into electrical signals amplified by the TIA 574. The amplified electrical signals output by the TIA 574 can then be further amplified by the limiting amplifier 580 (e.g., to the host) before being transmitted via or from the electrical interface 510.

[0082] The MCU 550 controls the power of the data signal from the laser driver 520, the voltage or current of the bias signal provided by the bias control circuit 525, and the gain of the TIA 574 and / or the limiting amplifier 580. The MCU 550 also controls the temperature control circuit 590, which in turn controls the temperature of the LD 532 and optionally the modulator 534. Typically, the temperatures of the LD 532 and the modulator 534 can be controlled by adjusting the power supplied to them (e.g., reducing the bias from the bias control circuit when the temperature of the LD 532 is too high, and increasing the bias from the bias control circuit when the temperature of the LD 532 is too low).

[0083] Exemplary methods using optical multiplexers or optical demultiplexers

[0084] Another aspect of the invention relates to a method for forming a multi-channel optical output signal, comprising using a first beam combiner to combine a first plurality of individual optical signals having the same polarization state (e.g., S or P) into a first multi-channel polarized optical signal; using a second beam combiner to combine a second plurality of individual optical signals having another polarization state into a second multi-channel polarized optical signal; and using a polarization beam combiner to combine the first and second multi-channel polarized optical signals into a third multi-channel optical signal. The first beam combiner includes at least one first mirror and at least one first filter, the second beam combiner includes at least one second mirror and at least one second filter, and the beam combiner includes one or more third mirrors and one or more third filters. The third multi-channel optical signal is the multi-channel optical output signal, or at least a component of the multi-channel optical output signal. For example, the third multi-channel optical signal may be combined with one or more additional multi-channel optical signals before being output by the optical multiplexer.

[0085] In a further embodiment, the first beam combiner may include a first parallelogram shape block. The first mirror(s) may be located on the distal side of the first parallelogram shape block (i.e., away from the optical emitter), and the first filter(s) may be located on the proximal side of the first parallelogram shape block (i.e., closer to the optical emitter). Alternatively or additionally, the second beam combiner may include a second parallelogram shape block, in which case the second mirror(s) may be located on the distal side of the second parallelogram shape block, and the second filter(s) may be located on the proximal side of the second parallelogram shape block. Furthermore, the parallel sides of the first parallelogram shape block may be parallel to or substantially parallel to the parallel sides of the second parallelogram shape block.

[0086] In even further embodiments, combining the first plurality of individual optical signals includes passing each of the first plurality of individual optical signals through a corresponding first filter and using the first mirror(s) to reflect all but one of the first plurality of individual optical signals toward an adjacent first filter. Alternatively, combining the second plurality of individual optical signals may include passing each of the second plurality of individual optical signals through a corresponding second filter and using the second mirror(s) to reflect all but one of the second plurality of individual optical signals toward an adjacent second filter.

[0087] In some embodiments, the beam combiner includes a third parallelogram shape block, the third mirror(s) includes a non-selective mirror on a first surface of the third parallelogram shape block, and the third filter(s) includes a wavelength-dependent and / or polarization-dependent filter on a second surface of the third parallelogram shape block parallel to the first surface of the third parallelogram shape block. Furthermore, the method may typically further include passing each of the first and second plurality of individual optical signals through a corresponding lens before the first and second plurality of individual optical signals enter the first and second beam combiners.

[0088] Alternatively, the present invention relates to a method for separating an incoming multi-channel optical output signal into its individual optical signals, comprising separating the incoming multi-channel optical signal into first and second multi-channel optical signals using a beam splitter comprising one or more mirrors and one or more filters; separating the first multi-channel optical signal into a first plurality of individual optical signals using a first beam combiner comprising at least one mirror and a plurality of filters; and separating the second multi-channel optical signal into a second plurality of individual optical signals using a second beam combiner comprising at least one mirror and a plurality of filters. The number of individual optical signals in the first and second plurality of individual optical signals is the same as the number of channels in the incoming multi-channel optical signal.

[0089] Similar to methods for forming multi-channel optical output signals, the first and second beam combiners may include corresponding first and second parallelogram shape blocks. However, the mirror(s) may be located near the parallelogram shape block (i.e., away from the optical emitter), the filter(s) may be located far from the first parallelogram shape block (i.e., closer to the optical emitter), and the parallel side of the first parallelogram shape block may be parallel to or substantially parallel to the parallel side of the second parallelogram shape block. In some embodiments, the beam splitter includes a third parallelogram shape block, the third mirror(s) includes a non-selective mirror on a first surface of the third parallelogram shape block, and the third filter(s) includes a wavelength-dependent and / or polarization-dependent filter on a second surface of the third parallelogram shape block parallel to the first surface of the third parallelogram shape block.

[0090] In a further embodiment, separating the first and / or second multi-channel optical signals into corresponding individual optical signals includes passing one of the individual optical signals through a corresponding filter in the beam combiner and reflecting the remaining individual optical signals toward the mirror (or one or more), where the remaining individual optical signals are reflected toward an adjacent filter. Optionally, the last remaining individual optical signal may be reflected to a corresponding last optical signal detector. Furthermore, the method may typically further include passing each of the first and second plurality of individual optical signals through a corresponding lens before the first and second plurality of individual optical signals enter the first and second beam combiners.

[0091] Conclusion / Summary

[0092] Embodiments of the present invention advantageously provide optical multiplexers and demultiplexers, optical transmitters including said optical multiplexers, and methods of using such optical multiplexers and demultiplexers. By sharing a signal with one polarization state between two signals having another polarization state and by combining optical signals with different polarization states respectively, this optical multiplexer reduces four-wave mixing effects compared to the prior art.

[0093] The foregoing description of specific embodiments of the invention is presented for illustrative and descriptive purposes. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and it will be apparent that many modifications and variations are possible in light of the foregoing teachings. These embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling those skilled in the art to best utilize the invention and its various embodiments, and to make various modifications suitable for the particular purpose contemplated. The scope of the invention is defined by the appended claims and their equivalents.

Claims

1. An optical multiplexer, characterized by, comprises a first reflective surface and a first filter, the first beam combiner configured to combine a first optical signal and a second optical signal into a first multi-channel polarized optical signal, wherein the first optical signal has a first polarization state and a first wavelength, the second optical signal has the first polarization state and a second wavelength, and the first filter reflects the first optical signal and allows the second optical signal to pass through; a second beam combiner comprising a second reflective surface and a second filter, the second beam combiner configured to combine a third optical signal and a fourth optical signal into a second multi-channel polarized optical signal, wherein the third optical signal has a second polarization state and a third wavelength, the fourth optical signal has the second polarization state and a fourth wavelength, and the second filter reflects the third optical signal and allows the fourth optical signal to pass through; and a polarization beam combiner comprising a third reflective surface and a polarization filter, the polarization beam combiner configured to combine the first and second multi-channel polarized optical signals into a multi-channel output signal. further comprising an optical isolator in an optical path selected from the first multi-channel polarized optical signal, the second multi-channel polarized optical signal, and the multi-channel output signal, configured to isolate reflected light of the output signal passing through the optical isolator.

2. The optical multiplexer of claim 1, wherein, wherein the first beam combiner comprises a first parallelepiped-shaped block, the second beam combiner comprises a second parallelepiped-shaped block.

3. The optical multiplexer of claim 1, wherein, wherein the first reflective surface and the first filter are located on opposite sides of the first parallelepiped-shaped block, and the second reflective surface and the second filter are located on opposite sides of the second parallelepiped-shaped block.

4. The optical multiplexer of claim 3, wherein, the first beam combiner further comprises a first anti-reflection sheet or plate located on the same side of the first parallelepiped-shaped block as the first filter, and the second beam combiner further comprises a second anti-reflection sheet or plate located on the same side of the second parallelepiped-shaped block as the second filter.

5. The optical multiplexer of claim 4, wherein, the polarization beam combiner comprises a third parallelepiped-shaped block, the first non-selective mirror is located on a first surface of the third parallelepiped-shaped block, and the polarization state-dependent filter is located on a second surface of the third parallelepiped-shaped block parallel to the first surface of the third parallelepiped-shaped block.

6. The optical multiplexer of claim 1, wherein, further comprising first and second half-wave plates configured to change (i) initial polarization states of the first and second optical signals to the first polarization state or (ii) initial polarization states of the third and fourth optical signals to the second polarization state, respectively.

7. The optical multiplexer of claim 1, wherein, 8. The optical multiplexer of claim 1, wherein: ​ the first beam combiner further comprises a third filter and a fourth filter, the first beam combiner being further configured to combine a fifth optical signal and a sixth optical signal with the first and second optical signals into the first multi-channel polarized optical signal, wherein the fifth optical signal has the first polarization state and a fifth wavelength, the sixth optical signal has the first polarization state and a sixth wavelength, the third filter reflects the first and second optical signals and allows the fifth optical signal to pass, and the fourth filter reflects the first, second, and fifth optical signals and allows the sixth optical signal to pass; and the second beam combiner further comprises a fifth filter and a sixth filter, the second beam combiner being further configured to combine a seventh optical signal and an eighth optical signal with the third and fourth optical signals into the second multi-channel polarized optical signal, wherein the seventh optical signal has the second polarization state and a seventh wavelength, the eighth optical signal has the second polarization state and an eighth wavelength, the fifth filter reflects the third and fourth optical signals and allows the seventh optical signal to pass, and the sixth filter reflects the third, fourth, and seventh optical signals and allows the eighth optical signal to pass.

9. The optical multiplexer of claim 8, wherein, the first beam combiner comprises a first parallelepiped-shaped block, and the second beam combiner comprises a second parallelepiped-shaped block.

10. The optical multiplexer of claim 9, wherein: the first reflective surface is on a first side of the first parallelepiped-shaped block closest to the polarization beam combiner, the first, third, and fourth filters are on a second side of the first parallelepiped-shaped block farthest from the polarization beam combiner, the second reflective surface is on a first side of the second parallelepiped-shaped block closest to the polarization beam combiner, and the second, fifth, and sixth filters are on a second side of the second parallelepiped-shaped block farthest from the polarization beam combiner.

11. The optical multiplexer of claim 9, wherein, first, second, third, and fourth half-wave plates are further included, the first, second, third, and fourth half-wave plates being configured to change (i) initial polarization states of the first, second, fifth, and sixth optical signals to the first polarization state or (ii) initial polarization states of the third, fourth, seventh, and eighth optical signals to the second polarization state, respectively.

12. The optical multiplexer of claim 1, wherein, each of the single optical signals has a wavelength that differs from a wavelength of an adjacent one of the single optical signals by at least 0.4 nm.

13. An optical transmitter, characterized by comprising: the optical multiplexer of claim 1; a plurality of light sources (optical or optoelectronic emitters) configured to provide the first, second, third, and fourth optical signals; a plurality of lenses through which the first and second optical signals pass before entering the first beam combiner, and through which the third and fourth optical signals pass before entering the second beam combiner; and a package or housing that includes the optical multiplexer, the plurality of light sources, and the plurality of lenses. the first beam combiner further comprises a third filter and a fourth filter, the first beam combiner being further configured to combine a fifth optical signal and a sixth optical signal with the first and second optical signals into the first multi-channel polarized optical signal, wherein the fifth optical signal has the first polarization state and a fifth wavelength, the sixth optical signal has the first polarization state and a sixth wavelength, the third filter reflects the first and second optical signals and allows the fifth optical signal to pass, and the fourth filter reflects the first, second, and fifth optical signals and allows the sixth optical signal to pass; and the second beam combiner further comprises a fifth filter and a sixth filter, the second beam combiner being further configured to combine a seventh optical signal and an eighth optical signal with the third and fourth optical signals into the second multi-channel polarized optical signal, wherein the seventh optical signal has the second polarization state and a seventh wavelength, the eighth optical signal has the second polarization state and an eighth wavelength, the fifth filter reflects the third and fourth optical signals and allows the seventh optical signal to pass, and the sixth filter reflects the third, fourth, and seventh optical signals and allows the eighth optical signal to pass. the first beam combiner comprises a first parallelepiped-shaped block, and the second beam combiner comprises a second parallelepiped-shaped block.

10. The optical multiplexer of claim 9, wherein: the first reflective surface is on a first side of the first parallelepiped-shaped block closest to the polarization beam combiner, the first, third, and fourth filters are on a second side of the first parallelepiped-shaped block farthest from the polarization beam combiner, the second reflective surface is on a first side of the second parallelepiped-shaped block closest to the polarization beam combiner, and the second, fifth, and sixth filters are on a second side of the second parallelepiped-shaped block farthest from the polarization beam combiner. first, second, third, and fourth half-wave plates are further included, the first, second, third, and fourth half-wave plates being configured to change (i) initial polarization states of the first, second, fifth, and sixth optical signals to the first polarization state or (ii) initial polarization states of the third, fourth, seventh, and eighth optical signals to the second polarization state, respectively. each of the single optical signals has a wavelength that differs from a wavelength of an adjacent one of the single optical signals by at least 0.4 nm. comprising: the optical multiplexer of claim 1; a plurality of light sources (optical or optoelectronic emitters) configured to provide the first, second, third, and fourth optical signals; a plurality of lenses through which the first and second optical signals pass before entering the first beam combiner, and through which the third and fourth optical signals pass before entering the second beam combiner; and a package or housing that includes the optical multiplexer, the plurality of light sources, and the plurality of lenses.

14. The optical transmitter of claim 13, wherein, Also included is a fiber adapter or connector configured to receive an optical fiber that receives the multi-channel output signal from the optical multiplexer.

15. The optical transmitter of claim 13, wherein, Also included are first and second half-wave plates configured to change (i) an initial polarization state of the first and second optical signals to the first polarization state or (ii) an initial polarization state of the third and fourth optical signals to the second polarization state, wherein each of the plurality of light sources is on a single substrate.

16. An optical transceiver, comprising: Comprising: The optical transmitter of claim 13; an optical demultiplexer configured to separate an incoming multi-channel optical signal into first, second, third, and fourth received optical signals, the first received optical signal having the first polarization state and the first wavelength, the second received optical signal having the first polarization state and the second wavelength, the third received optical signal having the second polarization state and the third wavelength, and the fourth multi-channel polarization optical signal having the second polarization state and the fourth wavelength; and a plurality of photodetectors configured to convert the first, second, third, and fourth received optical signals into first, second, third, and fourth received electrical signals.

17. The optical transceiver of claim 16, wherein, The optical demultiplexer comprises: a polarization beam splitter comprising a polarization filter and a first reflective surface, the polarization beam splitter configured to separate a multi-channel optical input signal into first and second multi-channel polarization optical signals; a first beam splitter comprising a second reflective surface and a first filter, the first beam splitter configured to separate the first multi-channel polarization optical signal into first and second optical signals, the first optical signal having a first polarization state and a first wavelength, and the second optical signal having the first polarization state and a second wavelength; and a second beam splitter comprising a third reflective surface and a second filter, the second beam splitter configured to separate the second multi-channel polarization optical signal into third and fourth optical signals, the third optical signal having a second polarization state and a third wavelength, and the fourth optical signal having the second polarization state and a fourth wavelength.

18. The optical transceiver of claim 16, wherein, Also included are: a plurality of laser drivers configured to send data drive signals to the plurality of light sources; a plurality of amplifiers configured to amplify the first, second, third, and fourth received electrical signals; an electrical interface configured to receive data signals corresponding to the data drive signals from an external device and provide the amplified first, second, third, and fourth received electrical signals to the external device; and a microprocessor or microcontroller configured to control the plurality of laser drivers and the plurality of amplifiers and receive instructions and configuration information through the electrical interface.

19. An optical demultiplexer comprising: Comprising: a polarization beam splitter comprising a polarization filter and a first reflective surface, the polarization beam splitter configured to separate a multi-channel optical input signal into first and second multi-channel polarization optical signals; a first beam splitter comprising a second reflective surface and a first filter, the first beam splitter configured to separate the first multi-channel polarization optical signal into first and second optical signals, the first optical signal having a first polarization state and a first wavelength, and the second optical signal having the first polarization state and a second wavelength; and a second beam splitter comprising a third reflective surface and a second filter, the second beam splitter configured to separate the second multi-channel polarization optical signal into third and fourth optical signals, the third optical signal having a second polarization state and a third wavelength, and the fourth optical signal having the second polarization state and a fourth wavelength. a first beam splitter comprising a second reflective surface and a first filter, the first beam splitter configured to separate the first multi-channel polarized optical signal into first and second optical signals, the first optical signal having a first polarization state and a first wavelength, and the second optical signal having the first polarization state and a second wavelength; and a second beam splitter comprising a third reflective surface and a second filter, the second beam splitter configured to separate the second multi-channel polarized optical signal into third and fourth optical signals, the third optical signal having a second polarization state and a third wavelength, and the fourth optical signal having the second polarization state and a fourth wavelength.

20. The optical demultiplexer of claim 19, wherein: the polarization filter comprises a polarization state dependent filter configured to reflect the first multi-channel polarized optical signal and allow the second multi-channel polarized optical signal to pass; the first reflective surface comprises a first non-selective reflective surface configured to reflect the first multi-channel polarized optical signal toward the first beam splitter; the second reflective surface is located on a side of the first beam splitter closest to the polarization beam splitter; the first filter is located on a side of the first beam splitter farthest from the polarization beam splitter; the third reflective surface is located on a side of the second beam splitter closest to the polarization beam splitter; and the second filter is located on a side of the second beam splitter farthest from the polarization beam splitter. ​

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