An optical modulator comprising a waveguide for propagating an optical signal comprising a proximate arm configured to communicate a proximate portion of the optical signal, and a distal arm configured to communicate a distal portion of the optical signal, a proximate diode configured to modulate the proximate portion of the optical signal, a distal diode configured to modulate the distal portion of the optical signal, and an electrical input electrically coupled to opposite signed interfaces of the proximate diode and the distal diode such that an electrical driving signal propagated along the electrical input causes an equal and opposite modulation of the proximate portion of the optical signal in the proximate arm of the waveguide and the distal portion of the optical signal in the distal arm of the waveguide.

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Optical modulators are devices for modulating electrical data signals onto an optical carrier to create an optical signal. The modulation of the optical carrier may be performed by manipulating a property of the optical carrier. Depending on which property of the optical carrier is manipulated, the optical modulators may be categorized into different types, for example, intensity modulators for modifying optical signal amplitude, phase modulators for modulating a phase of the optical carrier, polarization modulators for modifying a polarization of the optical carrier, and spatial light modulators for varying a spatial property of the optical carrier.

SUMMARY

In one embodiment, the disclosure includes an optical modulator comprising a waveguide for propagating an optical signal comprising a proximate arm configured to communicate a proximate portion of the optical signal, and a distal arm configured to communicate a distal portion of the optical signal, a proximate diode configured to modulate the proximate portion of the optical signal, a distal diode configured to modulate the distal portion of the optical signal, and an electrical input electrically coupled to opposite signed interfaces of the proximate diode and the distal diode such that an electrical driving signal propagated along the electrical input causes an equal and opposite modulation of the proximate portion of the optical signal in the proximate arm of the waveguide and the distal portion of the optical signal in the distal arm of the waveguide.

In another embodiment, the disclosure includes a single-drive multi-segment optical modulator system comprising an optical modulator comprising a plurality of electrical segment inputs, a proximate waveguide arm configured to communicate a proximate half of an optical signal, and a distal waveguide arm configured to communicate a distal half of an optical signal, and a plurality of modulator segments such that each modulator segment is configured to modulate a corresponding electrical segment input onto both the proximate waveguide arm and the distal waveguide arm, and a drive circuit electrically coupled to the optical modulator and comprising a plurality of drivers corresponding to the plurality of modulator segments such that each driver outputs an electrical segment signal to a single corresponding electrical segment input to control modulation by a single corresponding modulator segment.

DETAILED DESCRIPTION

An optical modulator is a building block in optical communication systems. Optical modulators may be employed to enable optical systems for various applications, such as optical sensing, radio-frequency (RF) waveform generation for optical signal transmission, and optical signal processing. Among various optical modulators, Mach-Zehnder modulators (MZM) may be employed in optical communications. There are at least four parameters to characterize an optical modulator: Vπ, insertion loss, modulation speed, and modulation efficiency. Vπis a change in voltage required to achieve a π phase shift in an optical signal. A small Vπindicates that a small voltage induces a large phase shift, so an optical modulator with a small Vπconsumes relatively low power. Insertion loss is defined as the power loss due to the insertion of the optical modulator into a system and is proportional to the length of the optical modulator. Modulation speed corresponds to the maximum data rate of RF signals that the optical modulator can modulate onto the optical signal. Modulation efficiency indicates the rate of bits that can be encoded into a waveform and is inversely proportional to the product of Vπand L, where L is the length of the optical modulator required to achieve a π phase shift. In other words, a high modulation efficiency corresponds to a small product of Vπand L.

Disclosed herein are various embodiments for single-drive multi-segment modulator-driver systems with high modulation efficiency. The disclosed embodiments comprise a drive IC and a multi-segment modulator. The optical modulator in any of the embodiments herein comprises silicon, Indium Phosphide (InP), Gallium Arsenide (GaAs), lithium niobate (LiNbO3), or combinations thereof. The multi-segment modulator is suitable for high speed operations (e.g., >25 Gigabits per second (Gbps) modulation speed) and may be divided to a plurality of modulator segments. Each modulator segment may encode a portion of an electrical signal onto an optical carrier. Each modulator segment comprises a modulation element coupled to a proximate arm of an optical waveguide and a modulation element coupled to a distal arm of the optical waveguide. The proximate and distal arms are coupled together to allow modulated signal portions from both modulation elements in each modulation segment to be aggregated into a single optical signal. In an embodiment, the modulation elements are diodes (e.g. a proximate diode and a distal diode). A single electrical output from a single signal driver is coupled to each modulation segment. For example, the electrical output is coupled to a cathode of the proximate diode and to an anode of the distal diode, or vice versa. Since the diodes are electrically oriented in opposite directions (from the perspective of the driver), the electrical signal from the driver is applied to each waveguide arm in equal and opposite directions (e.g. different sign but same absolute value), which allows a single driver to replace a dual driver modulator system for each segment with no loss in modulation amplitude. By removing the extra driver, modulation properties for high speed applications can be achieved with reduced power, in a reduced space, with fewer components/lower product cost, etc. In an alternate embodiment, a single driver with two outputs may be employed for each modulation segment to double the modulation power applied to each waveguide arm without increasing the number of drivers.

FIG. 1is a schematic diagram of an embodiment of a Z-cut LiNbO3MZM-driver system100, where Z-cut indicates the polarization of crystals in the MZM is oriented in a Z-axis direction perpendicular to the surface as shown inFIG. 1. The Z-cut MZM-driver system100comprises a Z-cut MZM101and a pair of complementary drivers comprising a proximate driver110, and a distal driver135. Therefore, the Z-cut MZM101is sometimes referred to as a dual-drive MZM. The Z-cut MZM-driver system100may be configured as shown or in any other suitable manner. The Z-cut MZM101may be made of various materials. The materials may include ferroelectric or electro-optical crystals such as lithium niobate (LiNbO3). The Z-cut MZM101comprises an input optical waveguide105, a proximate arm waveguide120, a distal arm waveguide130, a proximate electrode140coupled to the proximate arm waveguide120, a distal electrode160coupled to the distal arm waveguide130, grounds150, and an output waveguide170.

The input optical waveguide105is configured to receive light and/or a modulated optical signal, communicate a proximate half/portion of the optical signal to the proximate arm waveguide120, and communicate a distal half/portion of the optical signal to the distal arm waveguide130, respectively. The proximate arm waveguide120is electrically coupled to the proximate electrode140, and the distal arm waveguide130is electrically coupled to the distal electrode160. The proximate arm waveguide120and the distal arm waveguide130are configured to communicate the proximate portion of the optical signal and the distal portion of the optical signal, respectively, across the electrodes140and160, respectively, for modulation and on to the output waveguide170. The output waveguide170is configured to aggregate the proximate portion of the optical signal and the distal portion of the optical signal and communicate the combined optical signal, for example for output to an external component such as another waveguide, a waveguide-fiber coupler coupled to an optical fiber, etc.

The proximate electrode140is coupled to the proximate driver110. The proximate driver110is configured to receive a proximate RF signal102, amplify the proximate RF signal102to create an amplified proximate RF signal115, and electrically communicate the amplified proximate RF signal115to the proximate electrode140. The proximate electrode140and the ground150are collectively configured to modulate the phase of the proximate portion of the optical signals by depleting free electrons in the proximate arm waveguide120. Phase modulation of the proximate portion of the optical signals is implemented by applying the amplified proximate RF signal115on the proximate arm waveguide120to selectively deplete (e.g. depletion mode) or introduce free electrons (e.g. accumulation mode) into the proximate arm waveguide120, thereby inducing changes of the refractive index of the proximate arm waveguide120. The changes in the refractive index of the proximate arm waveguide120alters the speed of the optical signals propagating through the proximate arm waveguide120, resulting in the phase modulation of the optical signals. The distal driver135receives and amplifies a distal RF signal104to create an amplified distal RF signal137and communicates the amplified distal RF signal137to the distal electrode160to modulate optical signals in the distal arm waveguide130in a substantially similar manner. Accordingly, the output of optical signals in the proximate arm waveguide120and the distal arm waveguide130can be combined into an optical output signal by independently operating the proximate driver110and the distal driver135using a push-pull operation.

The amplitude of the phase modulation of the proximate portion of the optical signals and the distal portion of the optical signals are positively proportional to the voltages of the amplified proximate RF signal115and the amplified distal RF signal137, respectively, relative to grounds150. The proximate RF signal102and the distal RF signal104have a phase difference of about 180 degrees. As a result, the phase modulations of the proximate portion of the optical signals and the distal portion of the optical signals have the same absolute values but different signs. In one embodiment, the proximate RF signal102and the distal RF signal104are generated by two different RF oscillators. In another embodiment, the proximate RF signal102and the distal RF signal104are generated by the same RF oscillator and one of the RF signals (e.g. the distal104) experiences a phase shift of 180 degrees with respect to the proximate RF signal due to an RF shifter.

In operation, the optical signals are directed to the input optical waveguide105and split into the proximate portion and the distal portion. The proximate portion of the optical signals travels in the proximate arm waveguide120and experiences a proximate phase modulation. The distal portion of the optical signals is communicated in the distal arm waveguide130and experiences a distal phase modulation. The amplitudes of the proximate phase modulation and the distal phase modulation have the same absolute values but different signs. Then the proximate portion of the optical signals is combined with the distal portion of the optical signals at the output optical waveguide170for communication to an external component.

FIG. 2is a schematic diagram of an embodiment of an X-cut LiNbO3MZM-driver system200, where X-cut indicates the X-axis direction is perpendicular to the surface as shown inFIG. 2, while the Z-axis (the polarization of the crystal) is perpendicular to the optical waveguides. The X-cut MZM-driver system200comprises an X-cut MZM201and a driver210. The driver210is similar to the proximate driver110and the distal driver135. The X-cut MZM201is sometimes referred to as a single drive MZM. The X-cut MZM-driver system200may be configured as shown or in any other suitable manner. The X-cut MZM201may be substantially similar to Z-cut MZM101with a different crystal polarization and comprises an input optical waveguide205, a proximate arm waveguide220, a distal arm waveguide230, grounds250, and an output waveguide260, which are similar to the input optical waveguide105, the proximate arm waveguide120, the distal arm waveguide130, grounds150, and the output waveguide170, respectively.

The X-cut MZM201comprises an electrode240, which is substantially similar to electrodes140and160, but is positioned between the proximate arm waveguide220and the distal arm waveguide230. The electrode240is electrically coupled to driver210. The driver210receives RF signal204, amplifies the signal to create an amplified RF signal215, and applies the amplified RF signal215, via the electrode240, between the proximate arm waveguide220and the distal arm waveguide230. The amplified RF signal215depletes or induces free electrons in the proximate arm waveguide220and the distal arm waveguide230between the electrode240and the grounds250. The polarizations of crystals in the proximate arm waveguide220and the distal arm waveguide230are configured in opposite directions along the Z-axis resulting in equal and opposite behavior (e.g. depletion or introduction of free electrons) when the amplified RF signal215is applied to the electrode. For example, the phase shifts of the optical carrier portions that travel in the proximate arm waveguide220and the distal arm waveguide230have the same absolute values but different signs. As such, optical carriers traversing both the proximate arm waveguide220and the distal arm waveguide230can be controlled in a push-pull manner by a single driver210. Accordingly, the X-cut MZM201generates the same amount of phase modulation as the Z-cut MZM101with fewer drivers given the same voltage and electro-optical coefficients. The benefits of the X-cut MZM-driver system201include simpler implementations, smaller total sizes of a whole driver-modulator system, and lower power consumptions.

In both the Z-cut MZM101and the X-cut MZM201, the capacitances in the proximate arm waveguides120and220and the distal arm waveguides130and230are relatively large. As a result, the applications of the Z-cut MZM101and the X-cut MZM201at high speeds (e.g., >25 Gbps modulation speed) are limited, since the modulation speed is inversely proportional to the capacitances. In addition, the propagation velocity of the RF signals traveling in the MZMs are far slower than the propagation velocity of the optical signals due to the large capacitances per unit length, since the propagation velocity of the RF signals traveling in the MZM is inversely proportional to the square root of the capacitance per unit length.

FIG. 3is a schematic diagram of an embodiment of a dual-drive multi-segment MZM-driver system300. The dual-drive multi-segment MZM-driver system300comprises a drive integrated circuit (IC)310and a multi-segment modulator360. The dual-drive multi-segment MZM-driver system300can be configured as shown or in any other suitable manner. The dual-drive multi-segment MZM-driver system300employs a plurality of modulator segments370, each with an aggregate capacitance that is substantially smaller than the capacitance of Z-cut MZM101and X-cut MZM201. The modulator segments370are synchronized by introducing timing delay(s) to a proximate RF signal320and a distal RF signal325to account for propagation delays of an optical signal traversing the multi-segment modulator360. As such, dual-drive multi-segment MZM-driver system300may be modulated at higher speeds than Z-cut MZM101and X-cut MZM201.

The drive IC310comprises segment drivers350for each modulator segment370, wherein the segment drivers350are electrically coupled via transmission lines345. The segment drivers350each comprise a proximate output352and a distal output354(e.g. two drivers) that modulate a corresponding modulator segment370in a push-pull manner similar to proximate driver110and distal driver135. The segment drivers350each generate a proximate output352and a distal output354by employing a proximate RF signal320and a distal RF signal325received via transmission lines345and input driver340. The proximate RF signal320and the distal RF signal325, are similar to the proximate RF signal102and the distal RF signal104, respectively. The drive IC310employs input driver340to amplify the proximate RF signal320and the distal RF signal325as needed for transmission via transmission lines345. Input driver340may operate in conjunction with grounded resistors330and335(e.g. 50 ohms (Ω) resistors) to perform impedance matching to prevent electrical characteristics of devices supplying the proximate RF signal320and the distal RF signal325from altering the electrical characteristics of drive IC310. The transmission lines are coupled via resistor342to complete the circuit of the transmission lines345. The drive IC310is coupled to a power source (e.g. a 5.2 volt (V) source) and a ground to receive operational power. The drive IC310is controlled via direct current (DC) controls312and314in the example shown. It should be noted that while eleven segment drivers350are shown, any number of segment drivers350can be employed to correspond with the number of modulator segments370.

The multi-segment modulator360comprises a proximate arm waveguide380and a distal arm waveguide390, which are similar to proximate arm waveguides120and220and distal arm waveguides130and230, respectively. The proximate arm waveguide380and the distal arm waveguide390propagate an optical carrier via modulator segments370and a bias segment365. Each modulator segment370comprises a pair of capacitors376positioned on or adjacent to each of the proximate arm waveguide380and the distal arm waveguide390. Each capacitor376on the proximate arm waveguide380(e.g. the proximate capacitor) is electrically coupled to the proximate output352of the corresponding segment driver350and each capacitor376on the distal arm waveguide390(e.g. the distal capacitor) is electrically coupled to the distal output354of the corresponding segment driver350. Accordingly, each capacitor376can deplete or augment the electrons in the corresponding waveguide arm380/390to modulate a portion/stage of the optical signal in a push-pull fashion in a manner similar to Z-cut MZM101based on the outputs of segment drivers350. The modulator segments370further comprise inductors372and resistors374for conditioning the proximate output352and the distal output354sent to the capacitors376. Each capacitor376is also coupled to a voltage source (or ground, depending on the embodiment) to manage depletion/augmentation across the waveguide arms. The bias segment365provides any needed corrective conditioning of the optical signal. The bias segment365comprises capacitors368for modulating the optical signal based on Mach-Zehnder Interferometer (MZI) bias controls362and364, as well as resistors366for conditioning the MZI bias signals as needed. The MZI bias controls362and364modulate the optical signal in a manner substantially similar to modulator segments370, but are employed for fine tuning of the modulated signal before the signal is aggregated for output.

In operation, the proximate RF signal320and the distal RF signal325are timed and propagated to each segment driver350and forwarded to each modulator segment370for modulation onto an optical carrier. As the optical carrier propagates along the waveguide arms380and390, the optical carrier is modulated at each modulator segment370. The proximate RF signal320and the distal RF signal325are timed so that the signals arrive at an appropriate modulator segment370at an appropriate point in time to match the velocity of the optical carrier, such that a complete modulated optical signal is received at the bias segment365for final aggregation and output. The multi-segment modulator360reduces the capacitance per segment compared to Z-cut MZM101and X-cut MZM201, but requires dual segments drivers350for each modulator segment370.

FIG. 4is a schematic diagram of an embodiment of a single-drive multi-segment MZM-driver system400. The single-drive multi-segment MZM-driver system400operates in a manner similar to dual-drive multi-segment MZM-driver system300, but employs a segment driver440for each modulator segment470. The single-drive multi-segment MZM-driver system400may be employed for high speed operations (e.g. larger than 25 Gigahertz (GHz)), but requires less power and less complexity than system300. The single-drive multi-segment MZM-driver system400is configured as shown, or in any other suitable manner, and comprises a drive IC410and a multi-segment modulator460.

The drive IC410comprises an input driver430, segment drivers440, and a transmission line450for propagating an RF input signal420, which are similar to input driver340, segment drivers350, and transmission lines345, respectively. Drive IC410differs from drive IC310as drive IC410contains a single RF input signal420and a single segment driver440for each modulator segment470of the multi-segment modulator460. Drive IC410may also comprise resistors/inductors for impedance matching, DC controls and/or a power supply as needed. While eleven segment drivers440are shown, any number of segment drivers440can be employed to correspond with the number of modulator segments470. The segment drivers440may be implemented as complementary metal-oxide-semiconductor (CMOS) invertors, which consume relatively low power. Each segment driver440receives a single input and communicates a single output. A time delay between the segment drivers440for velocity matching with the optical signal is provided to transmission line450by the RF input signal420. The delay can also be generated actively by one or more CMOS circuits. By selectively disabling the segment drivers440over time (e.g. output set to low or high), a multi-level optical signal, such as pulse amplitude modulation (PAM) can be generated, even if the outputs of the drivers440have only two electrical levels.

The multi-segment modulator460may be made of silicon, Indium Phosphide (InP), and/or or Gallium Arsenide (GaAs). The multi-segment modulator460comprises a proximate arm waveguide480and a distal arm waveguide490, which are similar to proximate arm waveguide380and distal arm waveguide390, respectively, modulated by a plurality of modulator segments470corresponding to the segment drivers440. Each modulator segment470comprises a proximate diode476and a distal diode475, positioned on/adjacent to the proximate arm waveguide480and the distal arm waveguide490, respectively. The diodes475and476may also be referred to as positive-negative (p-n) diodes, and may act as voltage controlled variable capacitors. The diodes475and476may be oriented in with the same polarity as an X-cut MZM201. The diodes475and476each comprise a negatively charged cathode and a positively charged anode. Each segment driver440may be coupled to the cathode of the proximate diode476and the anode of the distal diode475, as shown inFIG. 4. Alternately, each segment driver440may be coupled to the anode of the proximate diode476and the cathode of the distal diode475. In either case, the segment driver440is coupled to a negative portion of one diode and a positive portion of the other diode such that each diode in a segment pair has an opposite polarity with respect to the segment driver440. The interface of each diode that is not coupled to a segment driver440may be coupled to a ground to support alternating current (AC) signals. DC isolation may be employed so that the diodes are biased at desired DC voltages. For example, DC isolation can be implemented by inserting large capacitors between each diode475and476and the respective ground. Because the polarity of the diode on each arm is aligned oppositely with each other in reference to the signal connection point, a driving signal results in an opposite phase shift, but in equal value, on each arm of the waveguide. As such, a single segment driver440generates the same amount depletion/accumulation (and hence modulation) on each waveguide arm as a pair of segment drivers350. Accordingly, by coupling the segment drivers440to a pair of oppositely charged diodes475and476, the number of transmission lines450and segment drivers440can be reduced by half when compared with dual-drive multi-segment MZM-driver system300, while maintaining the same modulation power, optical signal amplitude, modulation speed, etc.

FIG. 5is a schematic diagram of another embodiment of a single-drive multi-segment MZM-driver system500. The single-drive multi-segment MZM-driver system500is substantially similar to single-drive multi-segment MZM-driver system400, but each segment driver540of the drive IC510employs both a primary output and a complementary output based on a single RF input signal520received via an input buffer530and a transmission line550. The primary output is the same as the complementary output, but comprises an opposite electrical charge/sign. For example, if the primary output is about +0.5 volts, the complementary output is about −0.5 volts at the same time. The drive IC510, the RF input signal520, the input buffer530, transmission line550, and segment drivers540, may otherwise be substantially similar to drive IC410, RF input signal420, input driver430, transmission line450, and segment drivers440, respectively. The single-drive multi-segment MZM-driver system500may further comprise a multi-segment modulator560comprising a proximate arm waveguide580, distal arm waveguide590, and modulator segments570comprising distal diodes575and proximate diodes576, which may be similar to multi-segment modulator460, proximate arm waveguide480, distal arm waveguide490, modulator segments470, distal diodes475, and proximate diodes476, respectively. The primary output of each segment driver540is coupled to the cathode of the proximate diode576and the anode of the distal diode575while the complementary output is coupled to the anode of the proximate diode576and the cathode of the distal diode575, or vice versa (e.g. the primary output is coupled to different interfaces than the complementary output). By replacing the ground connections from modulator segments470with a complementary output, the effective driving voltage of each modulator segment570is doubled without increasing the number of segment drivers540or transmission lines550. Similar to that inFIG. 4, DC isolations may be employed so that the diodes are biased at desired DC voltages. By doubling the voltage of the output to each modulator segment570a larger differential phase shift and thus higher modulation depth may be achieved resulting in greater modulation efficiency. Further, the length of the MZM may be shortened resulting in greater modulation efficiency.

FIG. 6is a schematic diagram of an embodiment of a network element (NE)600. The NE600includes ingress ports610and receiver units (Rx)620for receiving data, a processor, logic unit, or central processing unit (CPU)630to process the data; optical transmitter units (Tx)640and egress ports650for modulating the data on optical signals and transmitting the optical signals; and a memory660for storing the data. The Tx640may comprise the single-drive multi-segment MZM-driver systems400and/or500. The network element600may be configured as shown or in any other suitable manner.

The processor630is configured to process the data and is in communication with the ingress ports610, receiver units620, transmitter units640, egress ports650, and memory660. The memory660includes one or more disks, tape drives, and solid-state drives and may be used as an over-flow data storage device, to store programs when such programs are selected for execution, and to store instructions and data that are read during program execution. The memory660may be volatile and non-volatile and may be read-only memory (ROM), random-access memory (RAM), ternary content-addressable memory (TCAM), and static random-access memory (SRAM).

In some embodiments, the NE600is programmed to generate the proximate RF signal102and the distal RF signal104. In some embodiments, the NE600is programmed to generate the RF signal204. In some embodiments, the NE600is programmed to generate the proximate RF signal320, the distal RF signal325, the MZI bias controls362and364, and the DC controls312and314. In some embodiments, the NE600is programmed to generate the RF signal420. In some embodiments, the NE600is programmed to generate the RF signal520.