Patent Description:
In various photonic circuit elements, such as switches, modulators, and Variable Optical Attenuators (VOA), input optical signals are split and/or combined to produce various output optical signals of desired amplitudes. Extinction of an optical signal may occur by splitting an input optical signal into two signals and combining the two signals to interfere with one another so that an output optical signal has a reduced amplitude from that of the input optical signal. An extinction ratio (re) can be calculated based on the relative amplitude of the output optical signal to the input optical signal, which may be presented as a fraction, a percentage, or in decibels based on the amplitudes of the inputs and outputs (e.g., re = Aoutput/Ainput). In several photonic circuits, it is desirable to produce an output signal such that re is below a threshold, so that downstream circuit elements are not inadvertently activated and so that carrier waves are suppressed for signal analysis.

<CIT> discloses an optical device comprising a tunable optical frequency comb generator. The comb generator includes an interferometer, and an optical feed-back loop waveguide and an electronic controller. An article entitled "<NPL> discloses a monolithically integrated photonic phase-sensitive amplification chip, on which two tunable laser pumps that are coherently injection-locked, respectively, from two first-order sidebands of an externally modulated tone are generated to enable signal-degenerate dual-pumped phase-sensitive amplification in a saturated semiconductor optical amplifier.

Another optical device according to the state of the art is known from <CIT>.

One embodiment presented in this disclosure provides a Photonic Element (PE), comprising: an input, configured to receive an input optical signal and split the input optical signal into a first partial signal and a second partial signal; a first arm connected to the input and configured to receive the first partial signal, the first arm including: a first phase shifter; and a first intensity modulator configured to provide a first matched signal based on the first partial signal; a second arm connected to the input and configured to receive the second partial signal, including: a second phase shifter, wherein the second phase shifter is configured to operate with the first phase shifter to phase offset the first partial signal relative to the second partial signal; and a second intensity modulator configured to provide a second matched signal based on the second partial signal, wherein only the second intensity modulator is configured to receive power from a power supply, whereby, in use, the second intensity modulator actively reduces the second matched signal from the second partial signal; and an output, connected to the first arm and the second arm and configured to combine the first matched signal and the second matched signal to provide an output signal with an amplitude below an activation threshold for downstream devices.

The present disclosure provides systems and methods for improving extinction ratios in silicon photonic elements. In optical signaling, to extinguish an optical signal, that signal is split into two components, where the split signals are phase shifted by 1π radians (i.e., <NUM>°) from each other and recombined, so that one signal (ideally) cancels out the other. For example, a sinusoidal signal with an amplitude of <NUM> W may be split into two signals, each with an amplitude of <NUM> W and a sinusoidal waveform. If the two split signals are offset from each other by 1π radians, at every phase position in the waveform, the amplitude of a combined signal ideally is <NUM> W (i.e., Amplitudesplit1 + Amplitudesplit2 = Amplitudecombined = <NUM>).

In practice, however, beam splitters and transmission media within optical circuits have different loss ratios, which can lead to a combined signal with an amplitude other than <NUM> W. For example, if a Y-splitter (also referred to as a Y-combiner, depending on a mode of operation) does not evenly split the power of a received signal, one splitting arm would carry more power than the other splitting arm. Similarly, if one pathway in the photonic element induces a first loss on the split signal that is carried thereon, and a second pathway induces a second, different loss of on the split signal that is carried thereon, the amplitudes of split signals may not equal zero when recombined.

To account for the physical differences in splitting/combining hardware and transmission media, downstream systems (e.g., optoelectronic devices that receive the output of a recombined signal) may set higher activation or detection potentials, manufacturers may set tighter tolerances on the fabrication of splitting/combining hardware and transmission media (e.g., more even splits in Y-splitter and couplers), resonant devices (e.g., photonic rings), etc. These approaches are often cost intensive (i.e., are associated with high scrap/failure rates), wavelength dependent, and induce high insertion losses or back reflection in optoelectronic devices. The present disclosure provides systems and methods for the use of inserted intensity modulators that provide a small, actively-controlled loss in signal strength of one split signals to compensate for fabrication imperfections at time of test/calibration. The intensity modulators used according to the present disclosure may reduce scrap/failure rates, are not wavelength dependent, and do not induce high insertion losses or back reflection.

<FIG> illustrates an example optoelectronic circuit <NUM>. As illustrated, the optoelectronic circuit <NUM> includes an Electrical Integrated Circuit (EIC) <NUM>, a power supply <NUM>, a logic controller <NUM>, a Photonic Integrated Circuit (PIC) <NUM>, and Photonic Element (PE) <NUM>. An optoelectronic circuit <NUM> may include other components in addition to those illustrated, which have been omitted so as not to distract from the novelty of the present disclosure.

The EIC <NUM> includes a substrate (such as silicon) in which the other components are electrically coupled to one another via various traces, wires, vias, and intermediary components. The other components may be embedded in the substrate or connected to the EIC <NUM> via one or more of solder pads, epoxy, and wire bonding.

The power supply <NUM> includes one or more power sources integrated into the EIC <NUM> or connections made to power sources linked externally from the EIC <NUM>. Examples of power sources include, but are not limited to: batteries, solar cells, Alternating Current (AC) to Direct Current (DC) converters linked to external current sources, DC to AC converters linked to external current sources, power conditioners, transformers, and the like. The power supply <NUM> provides power to the various components of the EIC <NUM>, including the processor <NUM>, the PIC <NUM>, and the PE <NUM>.

The processor <NUM> includes logic used to control the various components of the optoelectronic circuit <NUM> and to send/receive optical signals via the PIC <NUM> and PE <NUM>. In various embodiments, the processor <NUM> is used in conjunction with an external processor or controller for test or calibration of the optoelectronic circuit <NUM>. The processor <NUM> may include programmable, hardwired, or "burned in" logic to control the operation of the optoelectronic circuit <NUM>, and may include non-transitory computer storage media to store data or logic in a computable readable format.

The PIC <NUM> may include a diode activated by an optical signal received externally from the optoelectronic circuit <NUM>, a laser source to produce optical signals that are transmitted from the optoelectronic circuit <NUM>, and additional components to convert electrical signals to/from optical signals. The PIC <NUM> includes the PE <NUM>, which may include an optical extinguisher to extinguish optical signals and/or switches to select between optical signals to send/receive. The optical extinguisher of the PE <NUM> receives an optical signal, splits the optical signal into two parts, phase shifts the two parts of the optical signal and combines those parts to provide an output optical signal with an amplitude below the activation threshold for downstream devices. In some embodiments, the optical extinguisher <NUM> may include switches at input and/or output that receive/transmit multiple optical signals. The switches may designate which optical signal of several received optical signals is to be extinguished, or may designate which downstream device is to be transmitted an extinguished optical signal versus an un-extinguished or reconstructed optical signal.

<FIG> each illustrate various examples of a PE <NUM>, which may be a component included in the PIC <NUM> to extinguish or select between optical signals with improved extinction ratios and low insertion losses according to aspects of the present disclosure. In each of the <FIG>, several physical components are illustrated that may carry an optical signal. For ease of understanding, various illustrations of the optical signals that are discussed as being carried on specific portions of the PE <NUM> are also illustrated with exemplary amplitudes. Signals with various different amplitudes (including zero amplitude; or no signal) and in different ratios than those illustrated addition are envisioned.

Each of the example PEs <NUM> are illustrated with sections that include: an input <NUM>, an output <NUM>, a first arm 220a (generally, arm <NUM>) running between the input <NUM> and the output <NUM>, and a second arm 220b running between the input <NUM> and the output <NUM> in parallel with the first arm 220a. More arms <NUM> than illustrated may be used in various embodiments with inputs <NUM> and outputs <NUM> having a correspondingly different splitting/combining ratio matched with one another within the PE <NUM>.

Each arm <NUM> of the PEs <NUM> includes a phase shifter <NUM>, which is a physical component that shifts the phase of a signal carried through that component. The embodiments herein can be used with various types of phase shifters <NUM> (both passive and active) to affect the phase of a signal carried in a given arm <NUM>, which may operate based on varying principals. For example, a thermo-optic phase shifter <NUM> applies a controlled temperature to the transmission path of the arm <NUM> through which a signal is transmitted to affect a phase at which the signal exits the phase shifter <NUM>. In some embodiments, the phase shifter <NUM> may be an electro-optic material, such as lithium niobate. Each phase shifter <NUM> ideally affects only the phase of signals passed therethrough, but in operation some losses in amplitude may be experienced, and different phase shifters <NUM> may impart different losses.

In a two-arm PE <NUM>, a first phase shifter 221a (included in a first arm 220a) and a second phase shifter 221b (included in a second arm 220b) may each be configured to impart up to a 2π radian shift in a signal carried on a respective arm <NUM>. One or both of the phase shifters <NUM> may be engaged to affect a phase shift on a respective arm <NUM> so that signals, when re-combined at the output <NUM>, are aligned at desired phases with one another. By shifting the relative phases of signals carried on parallel arms <NUM>, the phase shifters <NUM> align the respective signals to cause destructive or constructive interference; extinguishing or amplifying the amplitude of one or more signals.

Each arm <NUM> of the illustrated PEs <NUM> also includes an intensity modulator <NUM>, which affects a loss in the amplitude of a signal carried through that component. Each intensity modulator <NUM> includes an active portion, which imparts a controlled, variable loss to the amplitude based on a supplied voltage, and may optionally include passive portions to affect the amplitude without power input. In addition to amplitude modulation, an intensity modulator <NUM> may also induce phase modulation to signals carried through that component, which may be accounted for (and counteracted) when configuring the phase modulators <NUM> (from a DC or low speed perspective).

For example, a variable portion may be a low-doped semiconductor in a semiconductor-insulator-semiconductor-capacitor (SISCAP) arrangement that imparts a variable drop in optical signal strength. In other examples, a forward-biased PIN diode or a reverse biased PN junction device may be used in the intensity modulator <NUM>. During operation, a power supply <NUM> may power a first intensity modulator 222a and leave a second intensity modulator 222b unpowered so that the signal carried on the first arm 220a is reduced in amplitude to match the signal carried on the second arm 220b. Including an intensity modulator <NUM> in an arm induces a small loss in optical signal amplitude, even if not powered, but the loss imparted by an active intensity modulator <NUM> may be set so as to offset the loss of an inactive intensity modulator <NUM>. Similarly, an intensity modulator <NUM> can be selected to match to the transmission medium of the arm <NUM> such that passive losses may be minimized (e.g., kept at or below about <NUM> dB).

In some embodiments, a high-speed modulator <NUM> is included on the arms <NUM> to phase modulate optical signals with high frequencies/short wavelengths (e.g., radio frequency signals) in conjunction with the Direct Current/low-speed modulation provided by the phase shifters <NUM>. In a two-arm PE <NUM>, a first high-speed modulator shifter 223a (included in a first arm 220a) and a high-speed modulator 223b (included in a second arm 220b) may each be configured to impart up to a 2π radian shift in a high-speed signal carried on a respective arm <NUM>. One or both of the phase shifters <NUM> may be engaged to affect a phase shift on a respective arm <NUM> so that high-speed signals, when re-combined at the output <NUM>, are aligned at desired phases with one another. By shifting the relative phases of high-speed signals carried on parallel arms <NUM>, the high-speed modulators <NUM> align the respective signals to cause destructive or constructive interference; extinguishing or amplifying the amplitude of one or more high-speed signals. Each high-speed modulator <NUM> ideally affects only the phase of signals passed therethrough, but in operation some residual losses in amplitude may be experienced, and different phase shifters <NUM> may impart different losses that may be accounted for by the intensity modulators <NUM>. The high-speed modulator <NUM> may be a high-doped semiconductor that is part of a radio frequency data modulator, a Mach-Zehnder Interferometer, a high-frequency phase shifting device, or the like. In some embodiments, the PE <NUM> may omit high-speed modulators <NUM>, or may integrate high-speed modulators <NUM> into the phase shifters <NUM>. Additionally, several high-speed modulators <NUM> may be included on each arm <NUM>, with each high-speed modulator <NUM> driven by a different modulation signal to affect different portions of the signal carried on the arm <NUM>. For example, the phase shifter <NUM> may phase shift portions of the signal from <NUM> to about X Hz, a first high-speed modulator <NUM> on the same arm <NUM> as the phase shifter <NUM> may phase shift portions of the signal from about X Hz (e.g., <NUM>) to about Y Hz (e.g., <NUM>), and a second high-speed modulator <NUM> on the same arm <NUM> may phase shift portions of the signal from about Y Hz to about Z Hz.

Although shown with the phase shifter <NUM> and the high-speed modulator <NUM> upstream from the intensity modulator <NUM>, the order of phase shifters <NUM>, high-speed modulator <NUM>, and intensity modulators <NUM> in a given arm <NUM> may be altered. In one embodiment, a first arm 220a includes a first phase shifter 221a upstream from an included first intensity modulator 222a which is upstream from a first high-speed modulator 223a, whereas the second arm 220b (of the same PE <NUM> or a different PE <NUM>) includes a second phase shifter 221b downstream from an included second intensity modulator 222b that is downstream from an included second high-speed modulator 223b.

The power supply <NUM> included in an optoelectronic circuit <NUM> in which the PE <NUM> is a part of may be connected to each of the phase shifters <NUM> and intensity modulators <NUM>. The power supply <NUM> may provide power of a regulated amount to shift the phase of a signal on one or more arms <NUM> or to reduce the amplitude of a signal on one arm <NUM>.

<FIG> illustrates an example PE <NUM> with one input <NUM> and one output <NUM>. The input <NUM> of the example PE <NUM> in <FIG> is a Y-splitter (in a <NUM>:<NUM> ratio), and the output <NUM> is a Y-combiner (in a <NUM>:<NUM> ratio). Between the input <NUM> and the output <NUM>, are two arms <NUM>, each with a phase shifter <NUM>, a high-speed modulator <NUM>, and an intensity modulator <NUM>.

An input signal <NUM> of amplitude Ai is received at the input <NUM> and is split onto the first arm 220a as a first partial signal 250a (generally, partial signal <NUM>) with an amplitude Apa and is split onto the second arm 220b as a second partial signal 250b with an amplitude of Apb. As illustrated, Apa is greater than Apb, and is phase aligned with one another. The one or both of the first phase shifter 221a and the second phase shifter 221b may induce a phase offset between the first partial signal 250a and the second partial signal 250b. Similarly, (if included) one or both of the first high-speed modulator 223a and the second high-speed modulator 223b may induce a phase offset between the high-frequency components of the first partial signal 250a and the second partial signal 250b.

During operation, the power supply <NUM> provides one of the first intensity modulator 222a and the second intensity modulator 222b a voltage to induce a loss in one of the partial signals <NUM>. The first arm 220a provides a first matched signal 260a (generally, matched signal <NUM>) of amplitude Ama to the output <NUM>, and the second arm 220b provides a second matched signal 260b of amplitude Amb to the output <NUM> to be combined into an output signal <NUM> of amplitude Ao. In one embodiment, one of the intensity modulators <NUM> induces a loss into a respective partial signal <NUM> to account for an uneven split ratio at the input <NUM> of the input signal <NUM>, the transmission/insertion losses of the arms <NUM>, and/or an uneven split ratio at the output <NUM>.

As illustrated herein, Ama is equal to Amb, but in other embodiments Ama may be unequal to Amb to account for an uneven split ratio at the output <NUM>, or to provide an output signal <NUM> with an amplitude Ao that satisfies an extinction ratio threshold (relative to Ai), but that induces smaller losses on the partial signals <NUM> (and requires correspondingly less power to implement).

A user or manufacturer may specify extinction ratio thresholds and loss thresholds that the PE <NUM> is to satisfy, and may also specify how the PE <NUM> is to be calibrated within those thresholds to prioritize how the voltage to an active intensity modulator <NUM> is set. For example, an intensity modulator <NUM> supplied with X Volts may provide a PE <NUM> with an extinction ratio of <NUM> and with an induced loss of <NUM> dB, and that same intensity modulator <NUM> may provide the PE <NUM> with an extinction ratio of <NUM> and with an induced a loss of <NUM> dB when supplied Y Volts. If the extinction ratios and induced losses for both voltage X and voltage Y satisfy the associated thresholds, a calibration specification may indicate which voltage of X and Y is to be selected for use, or if (and how) a voltage between X and Y is to be selected for use.

<FIG> illustrates an example PE <NUM> with one input <NUM> and multiple paths at the output <NUM>. The input <NUM> of the example PE <NUM> in <FIG> is a Y-splitter (in a <NUM>:<NUM> ratio), and the output <NUM> is a <NUM>:<NUM> switch. Between the input <NUM> and the output <NUM>, are two arms <NUM>, each with a phase shifter <NUM>, a high-speed modulator <NUM>, and an intensity modulator <NUM>.

An input signal <NUM> of amplitude Ai is received at the input <NUM> and is split onto the first arm 220a as a first partial signal 250a with an amplitude Apa and is split onto the second arm 220b as a second partial signal 250b with an amplitude of Apb. As illustrated, Apa is greater than Apb, and are phase aligned with one another. One or both of the first phase shifter 221a and the second phase shifter 221b may induce a phase offset between the first partial signal 250a and the second partial signal 250b. Similarly, (if included) one or both of the first high-speed modulator 223a and the second high-speed modulator 223b may induce a phase offset between the high-frequency components of the first partial signal 250a and the second partial signal 250b.

During operation, one of the first intensity modulator 222a and the second intensity modulator 222b are provided a voltage to induce a loss in one of the partial signals <NUM>. The first arm 220a provides a first matched signal 260a (generally, matched signal <NUM>) of amplitude Ama to the output <NUM>, and the second arm 220b provides a second matched signal 260b of amplitude Amb to the output <NUM> to be combined into a first output signal 270a (generally output signal <NUM>) of amplitude Aoa and a second output signal 270b of amplitude Aob. One of the intensity modulators <NUM> may induce a loss into a respective partial signal <NUM> to account for an uneven split ratio at the input <NUM> of the input signal <NUM>, the transmission/insertion losses of the arms <NUM>, and an uneven split ratio at the output <NUM>.

As illustrated herein, Ama is equal to Amb, but in other embodiments Ama may be unequal to Amb to account for an uneven split ratio at the output <NUM>, or to provide output signals <NUM> with amplitudes Aoa and Aob that all satisfy an extinction ratio threshold (relative to Ai), but that induce smaller losses on the partial signals <NUM> (and requires correspondingly less power to implement).

The output <NUM> in <FIG> may specify which output path carries a recombined signal (i.e., on which the matched signals <NUM> re-constitute the input signal <NUM>) and which output path carries an extinguished signal (i.e., on which the match signals <NUM> cancel one another out). In the illustrated example, the first output pathway carries a first output signal 270a of the recombined signal (with amplitude Aoa as close to Ai as possible) and the second pathway carries a second output signal 270b of the extinguished signal (with amplitude Aob as close to <NUM> amplitude as possible). For example, when a first pathway of the output <NUM> that carries the first output signal 270a is active, the output <NUM> switches to provide Aoa at a maximum amplitude and Aob at a minimum amplitude. In contrast, when a second pathway of the output <NUM> that carries the second output signal 270b is active, the output <NUM> switches to provide Aob at a maximum amplitude and Aoa at a minimum amplitude. Depending on the physical characteristics of the output <NUM>, the differences between actual and nominal values at each pathway may be different; that is, in some instances, Δ(Ai,Aoa) ≠ Δ(Ai,Aoa) and/or Δ(<NUM>,Aob) ≠ Δ(<NUM>,Aob). Therefore, a configuration system may set the voltage provided to an active intensity modulator <NUM> to the voltage associated with a maximum extinction at one of the pathways, the voltage associated with a lowest loss at one of the pathways, or an intermediate voltage based on the prior voltages so that each of the amplitudes on each of the pathways to meet specified thresholds for loss and/or extinction.

<FIG> illustrates an example PE <NUM> with multiple inputs <NUM> and one output <NUM>. The input <NUM> of the example PE <NUM> in <FIG> is a <NUM>:<NUM> switch, and the output <NUM> is a Y-combiner (in a <NUM>:<NUM> ratio). Between the input <NUM> and the output <NUM>, are two arms <NUM>, each with a phase shifter <NUM>, a high-speed modulator <NUM>, and an intensity modulator <NUM>.

The input <NUM> in <FIG> allows the PE <NUM> to specify one of two pathways, carrying either a first input signal 240a (generally, input signal <NUM>) with amplitude Aia or a second input signal 240b with an amplitude Aib is split and transmitted over the arms <NUM>. For example, when the first pathway of the input <NUM> is active, the first input signal 240a is split into the first partial signal 250a and the second partial signal 250b. In contrast, when the second pathway of the input <NUM> is active, the second input signal 240b is split into the first partial signal 250a and the second partial signal 250b. Although Aia and Aib are illustrated at different amplitudes, Aia and Aib may be set to various amplitudes in various embodiments. For example, a first signal source may provide the first input signal 240a and a second signal source may provide the second signal source 240b, and the input <NUM> controls which particular input signal <NUM> is transmitted to the output <NUM>.

The selected input signal <NUM> is split onto the first arm 220a as a first partial signal 250a with an amplitude Apa and is split onto the second arm 220b as a second partial signal 250b with an amplitude of Apb. As illustrated, Apa is greater than Apb, and are phase aligned with one another. One or both of the first phase shifter 221a and the second phase shifter 221b may induce a phase offset between the first partial signal 250a and the second partial signal 250b. Similarly, (if included) one or both of the first high-speed modulator 223a and the second high-speed modulator 223b may induce a phase offset between the high-frequency components of the first partial signal 250a and the second partial signal 250b.

During operation, one of the first intensity modulator 222a and the second intensity modulator 222b are provided a voltage to induce a loss in one of the partial signals <NUM>. The first arm 220a provides a first matched signal 260a (generally, matched signal <NUM>) of amplitude Ama to the output <NUM>, and the second arm 220b provides a second matched signal 260b of amplitude Amb to the output <NUM> to be combined into an output signal <NUM> of amplitude Ao. One of the intensity modulators <NUM> may induce a loss into a respective partial signal <NUM> to account for an uneven split ratio at the input <NUM> of the input signal <NUM>, the transmission/insertion losses of the arms <NUM>, and an uneven split ratio at the output <NUM>.

A controller may set the voltage provided to the active intensity modulator <NUM> (of the two intensity modulators <NUM>) to account for split ratios at the output <NUM>, losses in the arms <NUM>, and differences in the multiple pathways of the input <NUM>. For example, when the first signal 240a is carried on the arms <NUM>, the controller may measure a first extinction ratio and a first loss rate for Ao and Aia, but when the second signal 240b is carried on the arms <NUM>, the controller may measure a second extinction ratio and a second loss rate for Ao and Aib. In various embodiments, the controller may use thresholds to select the voltage for the intensity modulator <NUM> that produces the best extinction ratio between Ao and Aia based on the first input signal 240a or the best extinction ratio between Ao and Aib based on the second input signal 240b. In other embodiments, the controller may use thresholds to select the voltage for the intensity modulator <NUM> that produces the lowest losses between Ao and Aia based on the first input signal 240a or the lowest losses ratio between Ao and Aib based on the second input signal 240b. In further embodiments, the controller may set an intermediate voltage between those associated with the maximum extinction or lowest losses for a given input pathway so that the extinction/loss thresholds associated with the signals carried from the other input pathway may be satisfied.

<FIG> illustrates an example PE <NUM> with multiple inputs <NUM> and multiple outputs <NUM>. The input <NUM> of the example PE <NUM> in <FIG> is a <NUM>:<NUM> switch, and the output <NUM> is a <NUM>:<NUM> switch. Between the input <NUM> and the output <NUM>, are two arms <NUM>, each with a phase shifter <NUM>, a high-speed modulator <NUM>, and an intensity modulator <NUM>.

The output <NUM> in <FIG> may specify which output path carries a recombined signal (i.e., on which the matched signals <NUM> re-constitute the input signal <NUM>) and which output path carries an extinguished signal (i.e., on which the match signals <NUM> cancel one another out). In the illustrated example, the first output pathway carries a first output signal 270a of the recombined signal (with amplitude Aoa as close to the Ai of the selected input signal 240a or 240b as possible) and the second pathway carries a second output signal 270b of the extinguished signal (with amplitude Aob as close to <NUM> amplitude as possible). For example, when a first pathway of the output <NUM> that carries the first output signal 270a is active, the output <NUM> switches to provide Aoa at a maximum amplitude and Aob at a minimum amplitude. In contrast, when a second pathway of the output <NUM> that carries the second output signal 270b is active, the output <NUM> switches to provide Aob at a maximum amplitude and Aoa at a minimum amplitude. Depending on the physical characteristics of the output <NUM>, the differences between actual and nominal values at each pathway may be different; that is, in some instances, Δ(Ai,Aoa) ≠ Δ(Ai,Aoa) and/or Δ(<NUM>,Aob) ≠ Δ(<NUM>,Aob). Therefore, a configuration system may set the voltage provided to an active intensity modulator <NUM> to the voltage associated with a maximum extinction at one of the pathways, the voltage associated with a lowest loss at one of the pathways, or an intermediate voltage based on the prior voltages so that each of the amplitudes on each of the pathways to meet specified thresholds for loss and/or extinction.

<FIG> is a flowchart illustrating general operations of a method <NUM> for calibrating a PE <NUM> for improving extinction ratios. Method <NUM> may be performed as part of a Built-In Self-Test (BIST) or calibration procedure for an IC, or may be performed separately from other calibration and test procedures. In various embodiments, an internal processor or logic controller built into an IC in which the PE <NUM> is included may control the operations within method <NUM>. In other embodiments, an external processor or logic controller that is part of a test machine in communication with the PE <NUM> may control the operations of method <NUM>.

Method <NUM> begins at block <NUM>, where the processor provides one or more test signals of known phase, wavelength, and amplitude to the PE <NUM>. The processor may control which input <NUM> or output <NUM> is active in a multiple input/output PE <NUM>, and will monitor the amplitudes of the output test signals against the input test signals to determine various extinction ratios (re) throughout method <NUM>.

At block <NUM>, the processor signals the phase shifters <NUM> and high-speed modulators <NUM> on each arm <NUM> in turn to sweep through the available phases. The processor may signal one or both phase shifters <NUM> and/or high-speed modulators <NUM> to adjust an amount of phase offset imparted on the split test signal so that the test signal carried in the first arm 220a of the PE <NUM> is offset by 1π radians from the test signal carried in the second arm 220b. Offsetting the phase of the signal carried by the first arm 220a by 1π radians from the test signal carried by the second arm 220b will allow the test signals, when recombined at the output <NUM>, to cancel each other out. Once phase positions for the phase shifters <NUM> and/or high-speed modulators <NUM> that are offset by 1π are identified, method <NUM> proceeds to block <NUM>, where the processor sets the phase shifters <NUM> and/or high-speed modulators <NUM> to the identified phase positions.

At block <NUM>, the processor controls an amount of voltage provided to the intensity modulators <NUM> and sweeps through the available voltages. During the voltage sweep, the processor identifies, at block <NUM>, the voltage (Vre-max) supplied to one of the intensity modulators <NUM> that corresponds to the maximum extinction of the test signal at the output <NUM>. The processor also identifies during the voltage sweep, at block <NUM>, the voltage (Vloss-min) supplied to one of the intensity modulators that corresponds to a minimum power loss in the signal (e.g., the output test signal that has an amplitude closest to the amplitude of the input test signal).

As only one intensity modulator <NUM> (or the active part thereof) is powered during operation of the PE <NUM>, the processor may test each intensity modulator <NUM> one at a time across the available voltage inputs. In some embodiments, the processor identifies the arm <NUM> on which the test signal of the higher amplitude is carried and only sweeps through the input voltages for the intensity modulator <NUM> for that arm <NUM>. In further embodiments, the processor sweeps through input voltages for a given intensity modulator <NUM> until an extinction ratio is identified as increasing from prior-tested input voltages. In other embodiments, the processor sweeps through all available input voltages for one or more of the intensity modulators <NUM>.

In some embodiments, method <NUM> returns to block <NUM> from block <NUM>, where the processor activates a different input <NUM> or output <NUM> (or combination thereof) to determine test characteristics for different components in the PE <NUM>. In additional embodiments, method <NUM> returns to block <NUM> from block <NUM>, where the processor provides test signals of different known phases, wavelengths, amplitudes than test signals that were previously evaluated. In embodiments that return to block <NUM>, block <NUM> and block <NUM> may be omitted from method <NUM> after being performed once.

In embodiments that identify multiple values for Vre-max and/or Vloss-min (e.g., calibrating with test signals with different characteristics or over different pathways through the PE <NUM>), the processor may retain separate values for each calibration setup, or may average values across calibration setups. For example, if the processor is instructed to calibrate the PE <NUM> with three test signals having different wavelengths, Vre-max for the first signal may be A volts, for the second signal may be B volts, and for the third signal may be C volts. In some embodiments, the processor may retain each value of A, B, and C as individual values of Vre-max that are associated with the tested wavelengths. In other embodiments, the processor combines the values of A, B, C into an aggregate Vre-max (e.g., as a mean value, a wavelength biased mean value, a median value, a linear or curvilinear formula for Vre-max based on wavelength). The multiple identified values for Vloss-min may also be retained individually or in aggregate.

When the processor has observed the performance of each input <NUM>, output <NUM>, and test signal type specified for calibration, method <NUM> proceeds to block <NUM>. At block <NUM> the processor sets the voltage for one of the intensity modulators <NUM> with respect to the identified voltage Vre-max associated with the greatest identified extinction ratio (per block <NUM>), and the identified voltage Vloss-min associated with the lowest identified losses in signal strength (per block <NUM>) according to a calibration specification for the PE <NUM>. The calibration specification determines what voltage the processor will set the intensity modulator <NUM> to with respect to minimum extinction ratios for each output <NUM>, a maximum allowable signal loss across the PE <NUM>, a preference for lower losses or greater extinction ratios at one or more outputs <NUM>, and the like. In embodiments that are calibrated for multiple inputs <NUM> or outputs <NUM>, or that are calibrated with multiple test signals, the calibration specification may indicate separate thresholds for re or loss for different pathways or signal characteristics.

Several PEs <NUM> that are calibrated according to different specifications may have identical values for each of Vre-max and Vloss-min and the processor sets the respective intensity modulators <NUM> of the several PEs to different values based on the different specifications. In a first example, a PE <NUM> set according to a specification for a greatest available extinction ratio will have one intensity modulator <NUM> set to Vre-max. In a second example, a PE <NUM> set according to a specification for a lowest available signal strength loss has one intensity modulator <NUM> set to Vloss-min. In a third example, a PE <NUM> set according to a specification for a greatest available extinction ratio with a signal strength loss above a threshold value may have the processor set the intensity modulator <NUM> to a voltage between Vre-max and Vloss-min. In a fourth example, a PE <NUM> set according to a specification for a greatest available extinction ratio for signals of wavelength λA and for signals of wavelength λB, may have the processor set the intensity modulator <NUM> to a voltage between the values of Vre-max associated with λA and λB. In embodiments that set the voltage to the intensity modulator <NUM> to a value other than Vre-max and Vloss-min, a linear or curvilinear equation based at least in part on Vre-max and Vloss-min may be used to select the voltage.

In the event that the processor cannot determine a voltage to satisfy each threshold set in the calibration specification, the PE <NUM> may be failed.

Once the intensity modulator <NUM> for the PE <NUM> has been set and the PE <NUM> has passed calibration, or the PE <NUM> has failed calibration, method <NUM> may then conclude.

In summary, improvements in extinguishing optical signals in silicon photonics may be achieved by supplying a test signal of known characteristics to a Photonic Element (PE) to extinguish the test signal via a first phase shifter and intensity modulator on a first arm of the PE and a second phase shifter and intensity modulator on a second arm of the PE; sweeping through a plurality of voltages at the first intensity modulator to identify a first voltage that is associated with an extinction ratio at an output of the PE that satisfies an induced loss threshold and a second voltage that is associated with an induced loss in the test signal at the output of the PE that satisfies an extinction ratio threshold; and setting the PE to provide an operational voltage to the first intensity modulator based on the first voltage and the second voltage.

Embodiments of the present disclosure are described with reference to flowchart illustrations and/or block diagrams of methods, apparatuses (systems) and computer program products according to embodiments presented in this disclosure.

These computer program instructions may also be stored in a computer readable storage medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable storage medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.

The flowchart and block diagrams in the Figures illustrate the architecture, functionality and operation of possible implementations of systems, methods, and computer program products according to various embodiments. In this regard, each block in the flowchart or block diagrams may represent a module, segment or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some other implementations, the functions noted in the block may occur out of the order noted in the figures.

Claim 1:
A Photonic Element, PE (<NUM>), comprising:
an input (<NUM>), configured to receive an input optical signal (<NUM>) and split the input optical signal into a first partial signal (250a) and a second partial signal (250b);
a first arm (220a) connected to the input (<NUM>) and configured to receive the first partial signal (250a), the first arm (220a) including:
a first phase shifter (221a); and
a first intensity modulator (222a) configured to provide a first matched signal (260a) based on the first partial signal (250a);
a second arm (220b) connected to the input (<NUM>) and configured to receive the second partial signal (250b), including:
a second phase shifter (221b), wherein the second phase shifter (221b) is configured to operate with the first phase shifter (221a) to phase offset the first partial signal (250a) relative to the second partial signal (250b); and
a second intensity modulator(222b) configured to provide a second matched signal (260b) based on the second partial signal (250b), wherein the second intensity modulator (222b), but not the first intensity modulator (222a), is configured to receive power from a power supply (<NUM>), whereby, when in use, the second intensity modulator (222b) actively reduces the second matched signal (260b) from the second partial signal (250b); and
an output (<NUM>), connected to the first arm (220a) and the second arm (220b) and configured to combine the first matched signal (260a) and the second matched signal (260b) to provide an output signal (<NUM>) with an amplitude below an activation threshold for downstream devices.