Method and system for integrated power combiners

A system for integrated power combiners is disclosed and may include receiving optical signals in input optical waveguides and phase-modulating the signals to configure a phase offset between signals received at a first optical coupler, where the first optical coupler may generate output signals having substantially equal optical powers. Output signals of the first optical coupler may be phase-modulated to configure a phase offset between signals received at a second optical coupler, which may generate an output signal having an optical power of essentially zero and a second output signal having a maximized optical power. Optical signals received by the input optical waveguides may be generated utilizing a polarization-splitting grating coupler to enable polarization-insensitive combining of optical signals. Optical power may be monitored using optical detectors. The monitoring of optical power may be used to determine a desired phase offset between the signals received at the first optical coupler.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

FIELD OF THE INVENTION

Certain embodiments of the invention relate to signal processing. More specifically, certain embodiments of the invention relate to a method and system for integrated power combiners.

BACKGROUND OF THE INVENTION

As data networks scale to meet ever-increasing bandwidth requirements, the shortcomings of copper data channels are becoming apparent. Signal attenuation and crosstalk due to radiated electromagnetic energy are the main impediments encountered by designers of such systems. They can be mitigated to some extent with equalization, coding, and shielding, but these techniques require considerable power, complexity, and cable bulk penalties while offering only modest improvements in reach and very limited scalability. Free of such channel limitations, optical communication has been recognized as the successor to copper links.

Optical communication systems have been widely adopted for applications ranging from internet backbone, local area networks, data centers, supercomputing, to high-definition video. Due to superior bandwidth and low loss, optical fibers are the medium of choice for transporting high-speed binary data.

BRIEF SUMMARY OF THE INVENTION

A system and/or method for integrated power combiners, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims.

DETAILED DESCRIPTION OF THE INVENTION

Certain aspects of the invention may be found in a system for integrated power combiners. Exemplary aspects of the invention may comprise a chip comprising an optical power combiner in a photonic circuit, where the optical power combiner comprises input optical waveguides, optical couplers, and output optical waveguides. Optical signals may be received in each of the input optical waveguides and phase-modulated to configure a phase offset between signals received at a first optical coupler, wherein the first optical coupler may generate output signals with substantially equal optical powers. One or both output signals of the first optical coupler may be phase-modulated to configure a phase offset between signals received at a second optical coupler. The second optical coupler generates an output signal in a first of the output optical waveguides having an optical power of essentially zero and an output signal in a second of the output optical waveguides having a maximized optical power. The optical couplers may comprise, for example, directional couplers, and the chip may comprise, for example, a CMOS chip. Optical signals received by the input optical waveguides may be generated utilizing a polarization-splitting grating coupler, wherein the polarization splitting grating coupler enables polarization-insensitive combining of optical signals utilizing the optical power combiner. Optical power in waveguides coupling the optical couplers may be monitored using optical detectors. The monitoring of optical power may be used to determine a desired phase offset between the signals received at the first optical coupler, and optical signals may be communicated to the optical detectors utilizing optical taps in the coupling waveguides.

FIG. 1Ais a block diagram of a photonically enabled CMOS chip comprising integrated power combiners, in accordance with an embodiment of the invention. Referring toFIG. 1A, there is shown optoelectronic devices on a CMOS chip130comprising optical modulators105A-105D, photodiodes111A-111D, monitor photodiodes113A-113H, and optical devices comprising taps103A-103K, optical terminations115A-115D, and grating couplers117A-117H. There are also shown electrical devices and circuits comprising amplifiers107A-107D, analog and digital control circuits109, and control sections112A-112D. The amplifiers107A-107D may comprise transimpedance and limiting amplifiers (TIA/LAs), for example.

Optical signals are communicated between optical and optoelectronic devices via optical waveguides110fabricated in the CMOS chip130. Single-mode or multi-mode waveguides may be used in photonic integrated circuits. Single-mode operation enables direct connection to optical signal processing and networking elements. The term “single-mode” may be used for waveguides that support a single mode for each of the two polarizations, transverse-electric (TE) and transverse-magnetic (TM), or for waveguides that are truly single mode and only support one mode whose polarization is TE, which comprises an electric field parallel to the substrate supporting the waveguides. Two typical waveguide cross-sections that are utilized comprise strip waveguides and rib waveguides. Strip waveguides typically comprise a rectangular cross-section, whereas rib waveguides comprise a rib section on top of a waveguide slab.

The optical modulators105A-105D comprise Mach-Zehnder or ring modulators, for example, and enable the modulation of the continuous-wave (CW) laser input signal. The optical modulators105A-105D comprise high-speed and low-speed phase modulation sections and are controlled by the control sections112A-112D. The high-speed phase modulation section of the optical modulators105A-105D may modulate a CW light source signal with a data signal. The low-speed phase modulation section of the optical modulators105A-105D may compensate for slowly varying phase factors such as those induced by mismatch between the waveguides, waveguide temperature, or waveguide stress and is referred to as the passive phase, or the passive biasing of the MZI.

The phase modulators may have a dual role: to compensate for the passive biasing of the MZI and to apply the additional phase modulation used to modulate the light intensity at the output port of the MZI according to a data stream. The former phase tuning and the latter phase modulation may be applied by separate, specialized devices, since the former is a low speed, slowly varying contribution, while the latter is typically a high speed signal. These devices are then respectively referred to as the LSPM and the HSPM. Examples for LSPM are thermal phase modulators (TPM), where a waveguide portion is locally heated up to modify the index of refraction of its constituting materials, or forward biased PIN junction phase modulators (PINPM) where current injection into the PIN junction modifies the carrier density, and thus the index of refraction of the semiconductor material. An example of an HSPM is a reversed biased PIN junction, where the index of refraction is also modulated via the carrier density, but which allows much faster operation, albeit at a lower phase modulation efficiency per waveguide length.

The outputs of the modulators105A-105D may be optically coupled via the waveguides110to the grating couplers117E-117H. The taps103D-103K comprise four-port optical couplers, for example, and are utilized to sample the optical signals generated by the optical modulators105A-105D, with the sampled signals being measured by the monitor photodiodes113A-113H. The unused branches of the taps103D-103K are terminated by optical terminations115A-115D to avoid back reflections of unwanted signals.

The grating couplers117A-117H comprise optical gratings that enable coupling of light into and out of the CMOS chip130. The grating couplers117A-117D may be utilized to couple light received from optical fibers into the CMOS chip130, and the grating couplers117E-117H may be utilized to couple light from the CMOS chip130into optical fibers. The grating couplers117A-117H may comprise single polarization grating couplers (SPGC) and/or polarization splitting grating couplers (PSGC). In instances where a PSGC is utilized, two input, or output, waveguides may be utilized.

The optical fibers may be epoxied, for example, to the CMOS chip, and may be aligned at an angle from normal to the surface of the CMOS chip130to optimize coupling efficiency. In an embodiment of the invention, the optical fibers may comprise single-mode fiber (SMF) and/or polarization-maintaining fiber (PMF).

In another exemplary embodiment, optical signals may be communicated directly into the surface of the CMOS chip130without optical fibers by directing a light source on an optical coupling device in the chip, such as the light source interface135and/or the optical fiber interface139. This may be accomplished with directed laser sources and/or optical sources on another chip flip-chip bonded to the CMOS chip130.

The photodiodes111A-111D may convert optical signals received from the grating couplers117A-117D into electrical signals that are communicated to the amplifiers107A-107D for processing. In another embodiment of the invention, the photodiodes111A-111D may comprise high-speed heterojunction phototransistors, for example, and may comprise germanium (Ge) in the collector and base regions for absorption in the 1.3-1.6 μm optical wavelength range, and may be integrated on a CMOS silicon-on-insulator (SOI) wafer.

The analog and digital control circuits109may control gain levels or other parameters in the operation of the amplifiers107A-107D, which may then communicate electrical signals off the CMOS chip130. The control sections112A-112D comprise electronic circuitry that enable modulation of the CW laser signal received from the splitters103A-103C. The optical modulators105A-105D may require high-speed electrical signals to modulate the refractive index in respective branches of a Mach-Zehnder interferometer (MZI), for example. In an embodiment of the invention, the control sections112A-112D may include sink and/or source driver electronics that may enable a bidirectional link utilizing a single laser.

In operation, the CMOS chip130may be operable to transmit and/or receive and process optical signals. The grating couplers117A-117D may be operable to receive optical signals from optical fibers coupled to the chip130and may convert the optical mode of the fiber into the much smaller mode of a Si waveguide fabricated on the CMOS SOI wafer. The grating couplers117A-117D may comprise a single-polarization or a polarization-splitting type: in the first case, only a specific polarization is coupled to a single Si waveguide, while in the second case, two orthogonal polarizations are split into two output waveguides.

Integrated photonics platforms allow the full functionality of an optical transceiver to be integrated on a single chip, the CMOS chip130, for example. A transceiver chip comprise opto-electronic circuits that create and process the optical/electrical signals on the transmitter (Tx) and the receiver (Rx) sides, as well as optical interfaces that couple the optical signal to and from one or more fiber. The signal processing functionality may comprise modulating the optical carrier, detecting the optical signal, splitting or combining data streams, and multiplexing or demultiplexing data on carriers with different wavelengths.

The light source may be external to the chip or may be integrated with the chip in a hybrid scheme. It is often advantageous to have an external continuous-wave (CW) light source, because this architecture allows heat sinking and temperature control of the source separately from the transceiver chip130. An external light source may also be connected to the transceiver chip130via a fiber interface.

An integrated transceiver may comprise at least three optical interfaces, including a transmitter input port to interface to the CW light source, labeled as CW Laser In101; a transmitter output port to interface to the fiber carrying the optical signal, labeled Optical Signals Out; and a receiver input port to interface to the fiber carrying the optical signal, labeled Optical Signals In.

Waveguide photodetectors may be incorporated in integrated optics platforms, where several components are integrated together on a single receiver chip, as illustrated inFIG. 1A. In this platform, light couplers, such as the optical couplers117A-117D, couple the optical signal from the fiber into optical waveguides110. The optical signal subsequently enters the waveguide detectors111A-111D, where it is converted to an electrical signal. In some embodiments, the coupler may comprise a grating coupler, in which case the fiber is oriented in a near normal configuration to the chip130surface.

In instances where the fiber medium carries the signal in a single optical mode, the receiver subsystem on the chip, comprising the light coupler, the waveguide, and the waveguide detector, may be designed to support a single mode. Because the single-mode fiber mode has two polarization states, the term “single-mode waveguide” is used both for waveguides that support a single mode for each of the two polarizations (TE and TM) or for waveguides that only support one mode whose polarization is TE, with the electric field parallel to the substrate.

The fibers may be either single-mode fibers (SMFs), polarization-maintaining fibers (PMFs) or some other fiber type. To facilitate efficient optical signal processing, the waveguides carrying the signal on the transceiver chip130may support one mode with a single polarization. In contrast, the optical mode in SMFs has two orthogonal polarizations. Since the CW light source has a well-defined polarization, one option is to employ PMFs in order to retain a single polarization throughout the system. However, PMFs are costly and more difficult to align accurately than SMFs. For this reason, SMFs may be used in an optical interconnect, thereby requiring input ports to accept signals in arbitrary polarizations. A polarization splitting grating coupler (PSGC) may be used to generate two optical modes from a received input optical signal. In an exemplary embodiment of the invention, an optical power combiner may be utilized to efficiently combine optical signals of unknown phase and intensity generated by the PSGC.

In an exemplary embodiment of the invention, the integrated power may enable locating the CW laser source remotely, with the optical source signal communicated to the CMOS chip130via optical fiber, as opposed to mounting a laser in the laser module147directly over a grating coupler.

FIG. 1Bis a diagram illustrating an exemplary CMOS chip, in accordance with an embodiment of the invention. Referring toFIG. 1B, there is shown the CMOS chip130comprising electronic devices/circuits131, optical and optoelectronic devices133, a light source interface135, CMOS chip front surface137, an optical fiber interface139, and CMOS guard ring141.

The light source interface135and the optical fiber interface139comprise grating couplers, for example, that enable coupling of light signals via the CMOS chip surface137, as opposed to the edges of the chip as with conventional edge-emitting devices. Coupling light signals via the CMOS chip surface137enables the use of the CMOS guard ring141which protects the chip mechanically and prevents the entry of contaminants via the chip edge.

The electronic devices/circuits131comprise circuitry such as the amplifiers107A-107D and the analog and digital control circuits109described with respect toFIG. 1A, for example. The optical and optoelectronic devices133comprise devices such as the taps103A-103K, optical terminations115A-115D, grating couplers117A-117H, optical modulators105A-105D, high-speed heterojunction photodiodes111A-111D, and monitor photodiodes113A-113H.

In an embodiment of the invention, the efficiency of receiver subsystems on the CMOS chip130may be increased by utilizing an optical power combiner to efficiently combine optical signals of unknown phase and intensity in the photonic circuits in the CMOS chip130. Other embodiments of the invention comprise a power equalizer, a polarization-insensitive combiner, a polarization controller, and a polarization-insensitive splitter.

FIG. 1Cis a diagram illustrating an exemplary CMOS chip coupled to an optical fiber cable, in accordance with an embodiment of the invention. Referring toFIG. 1C, there is shown the CMOS chip130comprising the CMOS chip surface137, and the CMOS guard ring141. There is also shown a fiber-to-chip coupler143, an optical fiber cable145, and an optical source assembly147.

The CMOS chip130comprising the electronic devices/circuits131, the optical and optoelectronic devices133, the light source interface135, the CMOS chip surface137, and the CMOS guard ring141may be as described with respect toFIG. 1B.

In an embodiment of the invention, the optical fiber cable may be affixed, via epoxy for example, to the CMOS chip surface137. The fiber chip coupler143enables the physical coupling of the optical fiber cable145to the CMOS chip130.

In an embodiment of the invention, the efficiency of receiver subsystems on the CMOS chip130may be increased by utilizing an optical power combiner to efficiently combine optical signals of unknown phase and intensity in the photonic circuits in the CMOS chip130. Other embodiments of the invention comprise a power equalizer, a polarization-insensitive combiner, a polarization controller, and a polarization-insensitive splitter.

In an exemplary embodiment of the invention, the integrated power may enable locating the CW laser source remotely, with the optical source signal communicated to the CMOS chip130via optical fiber, such as the optical fiber cable145, as opposed to mounting the laser directly over a grating coupler in the light source module147.

FIG. 2is a block diagram of an exemplary integrated transceiver, in accordance with an embodiment of the invention. Referring toFIG. 2, there is shown an optical source201, optical fibers203A-203C, and a transceiver chip210comprising a Tx input coupler205, optical waveguides207A and207B, a Tx processor209, a Tx output coupler211, a Rx input coupler213, and a Rx processor215. The transceiver chip210may, for example, be substantially similar to the CMOS chip130.

The source201may comprise a continuous wave (CW) optical source, such as a semiconductor laser, for example, that may provide an optical signal for the photonic circuitry in the transceiver chip210. The Tx input coupler205, the Tx output coupler211, and the Rx input coupler213may comprise grating couplers, for example, that may be operable to couple light signals into and/or out of the transceiver chip to and/or from the optical fibers203A-203C. The optical fibers203A-203C may comprise single-mode, polarization-maintaining, or other type of optical fiber.

The Tx processor209may comprise a signal processor that may be operable to modulate a CW optical signal utilizing an electrical signal to enable the communication of data from the transceiver chip210via the Tx output coupler211and the fiber203B. The Tx processor209may comprise optical modulators and associated control circuitry, for example, such as the optical modulators105A-105D, the control sections112A-112D, and the control circuits109. The Tx processor209may also comprise an optical wavelength multiplexer.

Similarly, the Rx processor215may be substantially similar to the Tx processor209, but operable to de-modulate optical signals received by the transceiver chip210via the optical fiber203C and the Rx input coupler213and extract electrical signals. The Rx processor215may comprise one or more photodetectors to convert a received optical signal to an electrical signal. The Rx processor215may also comprise an optical wavelength demultiplexer.

FIG. 3is a block diagram of an exemplary integrated transceiver with a polarization splitting function, in accordance with an embodiment of the invention. Referring toFIG. 3, there is shown an optical source301, optical fibers303A-303C, and a transceiver chip310comprising a Tx input coupler305, optical waveguides307A-307D, a Tx processor309, a Tx output coupler311, a Rx input coupler313, and a detector317. The transceiver chip310may be substantially similar to the CMOS chip130.

If the receiver signal processing function comprises simply the detecting an optical signal, as illustrated inFIG. 3, an exemplary embodiment comprises a polarization splitter function to the Rx input port. In this embodiment, a light signal with an arbitrary polarization state in the optical fiber303C is split into two separate optical waveguides307C and307D and is combined at the detector317. The Rx input coupler313may comprise a polarization-splitting grating coupler (PSGC). The intensity and phase of the light in each waveguide307C and307D is thus a function of the input polarization state into the transceiver chip310via the fiber303C.

The Tx input coupler305, the waveguides307A-307D, the Tx processor309, and the Tx output coupler311, for example, may be substantially similar to the corresponding elements described with respect toFIG. 2. The detector317may, for example, be substantially similar to the photodetectors111A-111D, described with respect toFIG. 1A.

In instances where additional signal processing is required before detection, such as optical monitoring or demultiplexing, then each signal processing element would be duplicated for each optical path, the optical waveguides307C and307D, as shown inFIG. 4.

FIG. 4is a block diagram of exemplary integrated transceiver with duplicate signal processors, in accordance with an embodiment of the invention. The transceiver chip410may, for example, be substantially similar to the transceiver chip310, described with respect toFIG. 3, but with the Rx processors415A and4158, which may, for example, be substantially similar to the Rx processor315, described with respect toFIG. 3. Thus, circuit complexity and power usage may be reduced by combining the signals in each path before communicating them to a single Rx processor.

Similarly, at the transmitter input, if the fiber403A connecting the light source401to the Tx input coupler405is single-mode, then light may be split into two waveguides, such that the Tx signal processor409would be duplicated, and the signals recombined before or at the transmitter output. Thus, circuit complexity could be further reduced both on the transmitter side and on the receiver side, with an opto-electronic circuit that combines the optical power from the outputs of the PSGCs efficiently.

FIG. 5is a block diagram of an exemplary optical power combiner, in accordance with an embodiment of the invention. Referring toFIG. 5, there is shown an optical power combiner500comprising input waveguides501A and501B, phase modulators503A and503B, optical couplers505A and505B, coupling waveguides517, and output waveguides507A and507B. The optical couplers505A and505B may be directional couplers, or multi-mode interference couplers, for example, and may exhibit a tapping ratio of approximately 50%, for example. The directional couplers may comprise a multi-stage directional coupler comprising a plurality of directional couplers cascaded in series. The coupling waveguides517may be operable to communicate optical signals between the couplers505A and505B and the phase modulators503A and503B.

The phase and the intensity in the two output waveguides emanating from a PSGC is unknown since it depends on the polarization state in the fiber, so the light from the waveguides may not be combined passively, such as physically joining the waveguides side-by-side. This would violate the physical principle known as the brightness theorem. Therefore, in an embodiment of the invention, the optical power combiner500exhibits adaptive control to achieve an in-phase combination of the two input signals regardless of the polarization state of the incoming light in the input waveguides501A and501B.

In an embodiment of the invention, the optical power combiner500combines light from the two input waveguides501A and501B into a single output waveguide, given arbitrary intensity and amplitude in the two input waveguides. The output may be from either the output waveguide507A or507B.

In an embodiment of the invention, the phase modulators may be adaptively adjusted to maximize the power in one of the output waveguides507A and507B for any input polarization state. Consequently, the signal is substantially extinguished in the alternate output waveguide. The amplitude of the light signal in input waveguides501A and501B may be considered the two components of a vector (within a phase factor) as

within a phase factor. After the coupler505A, the amplitudes become

with equal power in both arms. If now the phase modulator503B imparts a phase shift e2iθto the bottom waveguide, then before the coupler505B, the amplitudes will be

within a phase factor. After the coupler505B, we obtain

Since, depending on their design, the phase modulators503A and503B normally provide only positive or only negative phase shifts efficiently, it may be desirable to insert additional phase modulators into the waveguides in each stage.

FIG. 6is a block diagram of an exemplary optical power combiner with phase modulators in each waveguide stage, in accordance with an embodiment of the invention. Referring toFIG. 6, there is shown an optical power combiner600comprising input waveguides601A and601B, phase modulators603A and603B, optical couplers605A and605B, coupling waveguides617, and output waveguides607A and607B. The optical couplers605A and605B may be directional couplers, or multi-mode interference couplers, for example, and may exhibit a tapping ratio of approximately 50%, for example. The optical power combiner600may, for example, be substantially similar to the optical power combiner500but with phase modulators in each waveguide stage. The coupling waveguides617may be operable to communicate optical signals between the couplers605A and605B and the phase modulators603A-603D.

The optical power combiner600may be controlled, for instance, by using power monitors that tap some portion of the light off from both waveguides into detectors to monitor the signals, as illustrated further with respect toFIG. 7. The phase modulators603A and603B may be configured so that the power detected in each path following the coupler605A is approximately equal. The phase modulators603C and603D may then be configured by maximizing the power in the desired output waveguide607A or607B.

In another embodiment of the invention, the optical power combiner600may comprise a plurality of stages, with each stage comprising pairs of phase modulators/couplers. This may enable a larger capacity to correct for unknown polarization fluctuations and uneven power splitting in the optical couplers.

FIG. 7is a block diagram of an exemplary optical power combiner with phase modulators and power detection in each waveguide stage, in accordance with an embodiment of the invention. Referring toFIG. 7, there is shown an optical power combiner700comprising input waveguides701A and701B, phase modulators703A and703B, optical couplers705A and705B, output waveguides707A and707B, taps709A and709B, coupling waveguides717, and power detectors711A and711B. The optical couplers705A and705B may be directional couplers, or multi-mode interference couplers, for example, and may exhibit a tapping ratio of approximately 50%, for example. The optical power combiner700may, for example, be substantially similar than the optical power combiner600but with phase modulators in each waveguide stage. The coupling waveguides717may be operable to communicate optical signals between the couplers705A and705B, the phase modulators703A-703D, the taps709A and709B, and the detectors711A and711B.

The taps709A and709B may, for example, be substantially similar to the taps103A-103K described with respect toFIG. 1A, and may be operable to tap optical power from the optical signals received from the coupler705A such that a measurement of the optical power may be measured and still allow most of the optical signal to pass to the phase modulators703C and703D. The power detectors711A and171B may comprise photodetectors, for example, that may be operable to detect the magnitude of optical signals received from the taps709A and709B.

The optical power combiner700may be controlled by using the taps709A and709B to tap a portion of the light off from both waveguides into the detectors711A and711B to monitor the signals. The phase modulators703A and703B may be configured so that the power detected in each path following the coupler705A is approximately equal. The phase modulators703C and703D may then be configured by maximizing the power in the desired output waveguide707A or707B.

The combiner700may be part of a larger subsystem that also includes the control electronics used for monitoring the tapped signal and controlling the amount of phase shift in each phase modulator. The control electronics may be either external to the transceiver chip or integrated monolithically on the chip.

FIG. 8is a block diagram of an exemplary power equalizer, in accordance with an embodiment of the invention. Referring toFIG. 8, there is shown an optical power equalizer800comprising input waveguides801A and801B, a phase modulator803, an optical coupler805, and output waveguides807A and807B.

In certain applications, it is beneficial to distribute light equally between two waveguides, given a power imbalance between the two. The power equalizer800is substantially the first stage of an exemplary power combiner device, such as described with respect toFIG. 5, for example, and comprises two input waveguides801A and801B, a phase modulator803, a coupler805, and two output waveguides807A and807B.

In an embodiment of the invention, if the amplitudes of the light signal in waveguides801A and801B are written as

then configuring the phase modulator803to impart a phase shift e−iφin the input waveguide801B relative to the waveguide801A, the amplitude in the waveguides before the coupler805will be

within a phase factor. After the coupler805, the amplitudes become

Writing the amplitudes in terms of optical power,

that is, the powers in the output waveguides807A and807B are thus equal. As in the case of the power combiners600and700, the optical power equalizer800may be augmented with an additional phase modulator in the alternate input waveguide, a control system with taps and monitors, and control electronics.

FIG. 9is a block diagram of a polarization-insensitive combiner, in accordance with an embodiment of the invention. Referring toFIG. 9, there is shown a polarization-insensitive combiner900comprising an input fiber901, a polarization-splitting grating coupler915, phase modulators903A and903B, optical couplers905A and905B, coupling waveguides917, and output waveguides907A and907B. The coupling waveguides917may be operable to communicate optical signals between the couplers905A and905B, the polarization splitting grating coupler915, and the phase modulators903A and903B.

In an exemplary embodiment of the invention, the polarization-insensitive combiner900combines light from an arbitrary polarization state in the fiber901into a single waveguide on the transceiver chip, either output waveguide907A and907B depending on the control of the phase modulators903A and903B, thereby reducing the complexity of other opto-electronic circuits on the chip.

The polarization-splitting grating coupler915accepts light from the input fiber901. Light with an arbitrary polarization is redirected into the two output waveguides of the polarization-splitting grating coupler915, where the two signals can have an arbitrary phase and amplitude relationship. Using the combiner described with respect toFIG. 5following the polarization-splitting grating coupler915, the power is combined into a single output waveguide, either the waveguide907A or907B. The polarization-splitting grating coupler915may be replaced with any device having the functionality of a polarization splitter.

Controlling the phase modulators903A and903B may be achieved by maximizing the signal in the output waveguide,907A or907B, or minimizing the signal in the alternate waveguide. As in the case of the power combiner, the polarization-insensitive combiner900may be combined with an additional phase modulator in the alternate waveguides, a control system with taps and monitors, and control electronics. Furthermore, utilizing the polarization-insensitive combiner900at the transmitter input port allows connecting the CW light source to the transceiver chip using a single-mode fiber instead of a polarization-maintaining fiber, and on the receiver side, the polarization-insensitive combiner900used as the input port obviates the need for duplicating the signal processing circuits on the receiver.

FIG. 10is a block diagram of a polarization controller, in accordance with an embodiment of the invention. Referring toFIG. 10, there is shown a polarization controller1000comprising an input fiber1001, a polarization-splitting grating coupler1015, phase modulators1003A and1003B, optical couplers1005A and1005B, coupling waveguides1017, and an output waveguide1007. The coupling waveguides1017may be operable to communicate optical signals between the couplers1005A and1005B, the polarization splitting grating coupler1015, and the phase modulators1003A and1003B.

The polarization controller1000may substantially comprise the polarization-insensitive combiner900operating in reverse, such that it may be used to launch light into a fiber or waveguide in any desired polarization state. The input waveguide1007receives the optical signal coming from the rest of the opto-electronic circuit on the chip. By adjusting the two phase modulators1003A and1003B, an arbitrary polarization state may be generated in the output fiber1001. As in the case of the power combiners, the polarization controller1000may be combined with an additional phase modulator in the alternate waveguides, a control system with taps and monitors, and control electronics.

In another embodiment of the invention, the optical polarization controller1000may comprise a plurality of stages, with each stage comprising pairs of phase modulators/couplers. This may enable a larger capacity to correct for unknown polarization fluctuations and uneven power splitting in the optical couplers.

FIG. 11is a block diagram of a polarization-insensitive splitter, in accordance with an embodiment of the invention. Referring toFIG. 11, there is shown a polarization controller1100comprising an input fiber1101, a polarization-splitting grating coupler1115, a phase modulator1103, an optical coupler1105, coupling waveguides1117, and output waveguides1107A and1107B. The coupling waveguides1117may be operable to communicate optical signals between the coupler1105, the polarization splitting grating coupler1115, and the phase modulator1103.

In multi-channel parallel transceiver architectures, power from the light source is typically split between several channels. For a two-channel system, the CW light coupled onto the chip is split evenly between the two channels before it enters the modulators. In an exemplary embodiment of the invention, the first stage of the polarization-insensitive combiner1100may be utilized to achieve this functionality.

As described with respect to the power combiners, the phase modulator803may be adjusted so that the powers in the output waveguides1107A and1107B are substantially equal for an arbitrary input polarization of light in the fiber. In addition, as in the case of the power combiner, the polarization-insensitive combiner1100may be combined with an additional phase modulator in the alternate waveguide, a control system with taps and monitors, and control electronics.

In another embodiment of the invention, the polarization-insensitive combiner1100may also be used in a transmitter with more than two channels. For instance, in a four-channel device, the polarization insensitive combiner and splitter may be followed by a passive splitter to further subdivide the incoming CW light into four, with each pair of outputs being controlled to output equal powers via phase modulation adjustments. And in yet another embodiment of the invention, the polarization-insensitive combiner1100may also be used in the receiver of quadrature demodulation systems where light is split evenly between two waveguides after it is received from a fiber.

In an embodiment of the invention, a method and system are disclosed for a chip130,210,310,410comprising an optical power combiner500,600,700in a photonic circuit133, the optical power combiner500,600,700comprising input optical waveguides501A,501B,601A,601B,701A,701B, optical couplers505A,505B,603A-603D,705A,705B, and output optical waveguides507A,507B,607A,607B,707A,707B. Optical signals may be received in each of the input optical waveguides501A,501B,601A,601B,701A,701B and phase-modulated to configure a phase offset between signals received at a first optical coupler505A,605A,705A, where the first optical coupler505A,605A,705A, may generate output signals having substantially equal optical powers. One or both output signals of the first optical coupler505A,605A,705A may be phase-modulated to configure a phase offset between signals received at a second optical coupler505B,605B,705B, where the second optical coupler505B,605B,705B generates an output signal in a first of the output optical waveguides507A,507B,607A,607B,707A,707B having an optical power of essentially zero and an output signal in a second of the output optical waveguides507A,507B,607A,607B,707A,707B having a maximized optical power. The optical couplers505A,505B,605A,605B,705A,705B may comprise grating couplers, for example, and the chip may comprise, for example, a CMOS chip130. Optical signals received by the input optical waveguides501A,501B,601A,601B,701A,701B may be generated utilizing a polarization-splitting grating coupler313,413,915,1015,1115, where the polarization splitting grating coupler enables polarization-insensitive combining of optical signals utilizing the optical power combiner500,600. Optical power in waveguides517,617coupling the optical couplers505A,505B,605A,605B,705A,705B may be monitored using optical detectors711A,711B. The monitoring of optical power may be used to determine a desired phase offset between the signals received at the first optical coupler505A,605A,705A, and optical signals may be communicated to the optical detectors711A,711B utilizing optical taps709A,709B in the coupling waveguides517,617,717.