Optical Mach-Zehnder Superstructure Modulator

Abstract

An optical Mach-Zehnder superstructure modulator is disclosed. The optical Mach-Zehnder superstructure modulator can linearize the in-phase component and the quadrature component of an optical modulated optical signal at the same time, and reduce the modulated light insertion loss (MOIL) by adding the in-phase component and the quadrature component of the amplitude and / or phase modulated optical signal in phase using two high-speed phase modulators embedded in the optical Mach-Zehnder superstructure modulator.

Description

[0001] This application is a divisional application of an invention patent application with an application date of September 4, 2019, application number 201980058267.7, and invention name “Linearization of orthogonal optical modulators and reduction of modulated light insertion loss”.

[0002] The section headings used herein are for organizational purposes only and should not be construed as limiting the subject matter described in this application in any way.

[0003] CROSS-REFERENCE TO RELATED APPLICATIONS

[0004] This application is a non-provisional application of U.S. Provisional Patent Application Serial No. 62 / 727,979, entitled “Linearization and Reduction of Modulated Optical Insertion Loss for Quadrature Optical Modulator”, filed on September 6, 2018. The entire contents of U.S. Provisional Patent Application Serial No. 62 / 727,979 are incorporated herein by reference.

[0005] Introduction

[0006] Unless otherwise indicated herein, the materials described herein are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.

[0007] Modulated light waves are often used in high-speed optical communication systems to transmit digital information from a transmitter to a receiver. In many systems, information is transmitted using both amplitude and phase modulation schemes. By using such techniques, more information can be transmitted over the same optical frequency band compared to amplitude-only modulation. Examples include phase shift keying modulation techniques such as binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK), and quadrature amplitude modulation (QAM) techniques such as 8QAM, 16QAM, and 64QAM implemented using an in-phase quadrature modulator (IQM).

[0008] Inserting an optical modulator such as an IQM optical modulator in an optical path can cause insertion loss of the optical signal, thereby affecting the subsequent transmission and reception of the modulated signal. In addition, conventional amplification techniques may cause distortion of the various transmitted symbols represented by the constellation points indicating the modulated data. Therefore, there is a need for an optical modulator with lower optical insertion loss and / or other features that improve the ability to receive optical signals with high fidelity. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In conjunction with the accompanying drawings, the present teaching and its additional advantages according to preferred embodiments and exemplary embodiments are described in more detail in the following detailed description. It will be appreciated by those skilled in the art that the drawings described below are for illustrative purposes only. These drawings are not necessarily drawn to scale, but generally focus on illustrating the principles of the present teachings. The accompanying drawings are not intended to limit the scope of the applicant's teachings in any way.

[0010] Figure 1 A known in-phase quadrature (IQ) Mach-Zehnder superstructure modulator system is shown.

[0011] Figure 2A Shown are plots of the field transfer function (dashed line), the power transfer function (solid line), and example operating points for a Mach-Zehnder modulator.

[0012] Figure 2B Shown are a graph of the field transfer function (dashed line), the power transfer function (solid line), and another example operating point for a Mach-Zehnder modulator.

[0013] Figure 2C A phase diagram representing the output of a Mach-Zehnder modulator is shown.

[0014] Figure 3A A phase diagram representing the output from a known in-phase quadrature (IQ) superstructure modulator system is shown.

[0015] Figure 3B A constellation diagram for a Mach-Zehnder superstructure modulator configured for 4QAM / QPSK operation is shown.

[0016] Figure 3C A table including truth tables for a Mach-Zehnder superstructure modulator configured for 4QAM or QPSK modulation and the field and intensity values ​​at the output is shown.

[0017] Figure 4 An embodiment of an IQ Mach-Zehnder superstructure modulator system of the present teachings is shown.

[0018] Figure 5A A table including truth tables, DC and AC bias phases, and field and intensity values ​​at the output for an embodiment of a Mach-Zehnder superstructure modulator configured for 4QAM operation of the present teachings is shown.

[0019] Figure 5B Phase diagrams representing the output of a modulated output signal for an embodiment of a Mach-Zehnder superstructure modulator configured for 4QAM operation according to the present teachings and a known Mach-Zehnder superstructure modulator configured for 4QAM are shown.

[0020] Figure 5CConstellation diagrams representing modulated output signals for an embodiment of a Mach-Zehnder superstructure modulator configured for 4QAM operation according to the present teachings and the output of a known 4QAM configured Mach-Zehnder superstructure modulator are shown.

[0021] Fig. 6A A diagram showing the current teachings for a 1V π Embodiments of a 16QAM operated Mach-Zehnder superstructure modulator driving operating points and constellation diagrams of modulated output signals of a known 16QAM configured Mach-Zehnder superstructure modulator.

[0022] Figure 6B A diagram showing the current teachings for a 2V π An embodiment of a driven 16QAM operated Mach-Zehnder superstructure modulator and a constellation diagram of a modulated output signal of a known 16QAM configured Mach-Zehnder superstructure modulator.

[0023] Figure 6C The present teaching is configured for use with a 2V π Embodiments of driven and linearized 16QAM operated Mach-Zehnder superstructure modulators and constellation diagrams of modulated output signals of known 16QAM configured Mach-Zehnder superstructure modulators.

[0024] Fig. 7A A phase diagram for a 16QAM constellation is shown.

[0025] Figure 7B A table showing the symbols and the associated phase and amplitude of the transmitted optical carrier is presented. Fig. 7A The symbol of the phase diagram.

[0026] Figure 8 An implementation of a dual polarization IQ Mach-Zehnder superstructure modulator system of the present teachings is shown. DETAILED DESCRIPTION

[0027] References in the specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the teachings. The phrase "in one embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment.

[0028] It should be understood that the various steps of the method of this teaching can be performed in any order and / or simultaneously, as long as the teaching remains operable. In addition, it should be understood that the apparatus and method of this teaching can include any number or all of the described embodiments, as long as the teaching remains operable.

[0029] This teaching will now be described in more detail with reference to the exemplary embodiments shown in the accompanying drawings. Although this teaching is described in conjunction with various embodiments and examples, it is not intended that this teaching be limited to these embodiments. On the contrary, as will be appreciated by those skilled in the art, this teaching includes various alternatives, modifications and equivalents. Those of ordinary skill in the art who contact this paper teaching will recognize that additional implementations, modifications and embodiments, as well as other fields of use, are within the scope of the present disclosure described herein.

[0030] The present teachings describe a method for simultaneously linearizing an in-phase quadrature optical modulator and reducing modulated optical insertion loss (MOIL) by utilizing in-phase addition of in-phase quadrature components of an nQAM signal implemented using two high-speed phase modulators embedded in a superstructure Mach-Zehnder modulator. The modulators of the present teachings can be implemented in, for example, lithium niobate, indium phosphide, gallium arsenide, and silicon photonics technologies.

[0031] The systems and methods of the present teachings relate to linearization and / or reduction of modulated light insertion loss (MOIL) for Mach-Zehnder based in-phase quadrature optical modulators. More specifically, the systems and methods of the present teachings rely, at least in part, on the recognition that coherent (phase sensitive) optical signal combining methods can be used to reduce or eliminate the inherent modulated light insertion loss present in known Mach-Zehnder based in-phase quadrature optical modulators that rely on incoherent (phase insensitive) optical signal combining methods. The systems and methods can advantageously linearize the output modulated optical signals produced by the Mach-Zehnder based in-phase quadrature optical modulators. In addition, the systems and methods of the present teachings can advantageously control and / or improve the distance between points of the output modulated optical signal constellation produced by the Mach-Zehnder based in-phase quadrature optical modulators. This distance is sometimes referred to as the Hamming distance.

[0032] Figure 1 A known IQ Mach-Zehnder superstructure modulator system 100 is shown. A light source 110 generates an optical signal. In some configurations, the generated optical signal may be, for example, a coherent optical light wave also referred to as an optical carrier. In various configurations, the light source 110 may be a fixed wavelength or tunable wavelength light source. The light source 110 is connected to an input 121 of a master IQ Mach-Zehnder superstructure modulator 120. The optical signal at the input of the master Mach-Zehnder modulator (MZM) 120 is divided into two arms 112, 114 of the parent MZM 120 by an optical splitter 102. The first arm 112 includes a daughter MZM 130, and the second arm 114 includes a daughter MZM 140. The daughter MZM 130 includes two arms 123, 124, and the daughter MZM 140 includes two arms 125, 126.

[0033] Each sub-MZM 130, 140 includes a pair of modulation electrodes 131, 132, 141, 142, one for each arm 123, 124, 125, 126. Each sub-MZM 130, 140 also includes a pair of bias electrodes 151, 152, 161, 162, the bias electrodes 151, 152, 161, 162 for each arm 123, 124, 125, 126. The modulation electrodes 131, 132, 141, 142 and the bias electrodes 151, 152, 161, 162 are configured as a differential drive configuration, sometimes referred to as a push-pull configuration, which provides a positive signal to one arm 123, 125 of each sub-MZM 130, 140 and a negative signal to the other arm 124, 126 of each sub-MZM 130, 140. The equal and opposite drive configuration advantageously reduces the peak voltage of the drive signals applied to electrodes 131 , 132 , 141 , 142 , 151 , 152 , 161 , 162 to produce a phase difference between the modulated optical signals in arms 123 , 124 or in arms 125 , 126 .

[0034] The modulation electrodes 131, 132, 141, 142 are connected to the modulation driver 106, which provides RF modulation signals to the corresponding electrodes 131, 132, 141, 142. For example, the positive RF modulation V for the in-phase signal RF_I_P (t) Negative RF modulation V applied to the modulation electrode 131 of the sub-MZM 130 and used for the in-phase signal RF_I_N (t) is applied to the modulation electrode 132 of the sub-MZM 130. The electrodes 131, 132 apply a modulation phase to the optical signal passing through the first arm 112 based on the applied modulation signal. The bias electrodes 151, 152, 161, 162 are connected to the bias driver 108, which provides a DC bias signal to the corresponding bias electrodes 151, 152, 161, 162. For example, the positive bias signal V for the sub-MZM 130 DC_I_P is applied to the bias electrode 151 and is used for the negative bias signal V of the sub-MZM 130 DC_I_N is applied to bias electrode 152. In some configurations, the DC bias signal is configured to bias sub-MZM 130 at a minimum transmission point and to bias sub-MZM 140 at a minimum transmission point.

[0035] The optical signals from the two arms 112, 114 of the parent MZM 130 are combined to generate a combined optical signal output 122 through the combiner 103. The two arms 112, 114 of the parent MZM 130 have bias electrodes 171, 172 connected to a bias driver 109, which provides positive and negative DC bias signals to the bias electrodes 171, 172 to generate a bias phase for the optical signal in each arm 112, 114 of the parent MZM superstructure 120. In some configurations, the DC bias signal is configured to bias the parent MZM superstructure 120 at a quadrature point by generating a π / 2 phase difference between the optical signal generated in the first arm 112 and the optical signal generated in the second arm 114.

[0036] The bias drivers 108, 109 and the modulation driver 106 are controlled by the controller 104. In various configurations, the bias drivers 108, 109, the modulation driver 106 and / or the controller 104 are formed by one or more circuits. In various configurations, the circuits may include FPGAs, ASICs, DSPs, ADCs, DACs and / or other discrete components and / or circuits, alone or in combination.

[0037] In some configurations, the modulation driver 106 and the bias driver 108 are configured to generate ±1DPSK modulation using an RF modulation signal and a DC bias signal, so that one sub-MZM 130 applies a modulation phase to the optical signal in response to a first modulation signal, which causes an in-phase ±1DPSK modulation of the optical signal passing through the first arm 112. The other sub-MZM 140 applies a modulation phase to the optical signal in response to a second modulation signal, which causes an orthogonal ±1DPSK modulation of the optical signal passing through the second arm 114. The parent MZM 120 multiplies the ±1DPSK modulation generated in the second arm 114 by j by adding a π / 2 phase shift, thereby converting it into an orthogonal modulation. Then, the parent MZM 120 adds the two DPSK modulations generated by the first arm 112 and the second arm 114 to generate QPSK or 4QAM modulation in one polarization.

[0038] The IQ MZM superstructure modulator system 100 can be used to implement a variety of amplitude and phase based modulation schemes. The specific modulation scheme depends on the specific multi-level signal having a certain peak-to-peak voltage applied to the modulating sub-Mach-Zehnder modulator. For the superstructure Mach-Zehnder modulator, typically, the sub-Mach-Zehnder modulator is biased at the minimum transmission point, while the main Mach-Zehnder modulator is biased at the orthogonal transmission point.

[0039] Figure 2AA graph 200 is shown showing a field transfer function (dashed line), a power transfer function (solid line), and example operating points for a Mach-Zehnder modulator. The graph shows a quadrature point bias 202, V bias =V π / 2 and with V π The application of the peak-to-peak voltage swing 204 modulates the operating point of the drive signal. As shown by the solid line power transfer function, the operating point bias 202 and voltage swing 204 provide amplitude modulation from a zero state (no power output) to one state (full output power). The power transfer function also illustrates how the quadrature point bias 202 is located at the half power point of the modulator, which results in 3DB inherent losses. Back to Reference Figure 1 , similarly in some configurations, the main Mach-Zehnder modulator 120 is biased at the quadrature transmit point to introduce a π / 2 phase shift in the Mach-Zehnder superstructure.

[0040] Figure 2B A graph 220 showing a field transfer function (dashed line), a power transfer function (solid line), and another example operating point for a Mach-Zehnder modulator is shown. Graph 220 shows a minimum transmit bias 222 where the Mach-Zehnder is biased at the output for a nominally zero optical signal. From the field transfer function curve, it is shown that the input modulated signal 2V that produces a ±π phase change in the optical signal π The peak-to-peak voltage swing 204. As shown in the power transfer curve, at the minimum transmit operating point bias 222, there is a 2V π This operating point of the voltage swing also produces peak output power at each extreme of the applied voltage. Figure 1 , which operating point can be used to generate, for example, BPSK and / or DPSK signals from sub-Mach-Zehnder modulators 130 and 140 .

[0041] Figure 2C A phase diagram 240 representing the output of a Mach-Zehnder modulator is shown. The phase diagram 240 helps visualize the achievable signal space in the output of the Mach-Zehnder modulator. The phase diagram 240 includes a real axis 242 and an orthogonal imaginary axis 244. The unit amplitude transmission and phase shift of the modulated output signal are shown by a circle 245, which is composed of the angles subtended relative to the positive real axis 242. The Mach-Zehnder modulator optical signal output generated by applying the phase modulation signal can be represented by the phase angle 246, and amplitude 248, denoted by A. Four example output signal points 250, 252, 254, 256 are shown as specific examples. Each of the points 250, 252, 254, 256 has unit amplitude but a different phase. Specifically, the phase is: For output 250, For output 252, For output 252, and for output 252,

[0042] This set of four outputs 250, 252, 254, 256 can be demodulated in a coherent detector, and thus information can be encoded on an optical signal by applying a modulation signal to achieve one of these specific output points to encode a specific symbol of the information being transmitted. For the four different output points 250, 252, 254, 256, each point represents two bits of information encoded by the modulation signal. A modulation scheme that relies on outputs with four different phases and equal amplitudes is called QPSK. Other modulation schemes are also possible, including schemes that use outputs with different amplitudes and different phases. In the phase diagram, different amplitudes are represented by circles of different diameters. Various embodiments of the systems and methods of the present teachings can be applied to one or more of these so-called coherent or phase-sensitive modulation schemes.

[0043] Figure 3A A phase diagram 320 representing the output from a known superstructure modulator system 100 is shown. To simplify the description of the present teachings, it is assumed that all splitters split the power into two equal halves and that all combiners obtain the same amount of power from each contributing path. In some configurations, many other splitting and recombination ratios may be used. In addition, additional losses due to, for example, material transmission losses of light through the various components are not included in the analysis.

[0044] Reference Figure 1 , FIG. 2A to FIG. 2C and Figure 3A , both the in-phase sub-MZM 130 and the quadrature-phase sub-MZM 140 are at the minimum transmission point (e.g., Figure 2B The voltage is biased at ±1V. π or a peak-to-peak voltage swing of 2V π In addition, the parent MZM 120 is driven by a modulated AC waveform to generate DPSK modulation. Figure 2A The bias is provided differentially by a DC bias driver 109, which provides V to the bias electrode 171. DC_P_P and provides V to the bias electrode 172 DC_P_N This bias causes the phase in the second arm 114 to shift by +90 degrees relative to the first arm 112. The resulting output signal is Figure 3A The constellation points 334, 336, 338, 340 shown in FIG. Since both the in-phase modulated signal and the quadrature modulated signal are present at the output of the superstructure modulator, the quadrature bias point of the parent MZM 120 inherently produces a 3dB insertion loss. This is based on Figure 2AThe power transfer function is clear.

[0045] The field at the output of the MZM superstructure system 100 can be mathematically described as:

[0046]

[0047]

[0048] in, V I (t)=±V π and V Q (t)=±V π V I (t) = V I (t) = V RF_I_P (t)-V RF_I_N (t), and Take the real part of the complex signal in brackets. Voltage V π , also known as V pi , is the driving voltage required to produce a π degree phase shift on the optical signal. The ±1 in the field is related to the data modulation φ I (t) corresponds to a 0 or π degree phase shift in the modulated optical E field at the output of the in-phase or first arm 112 of the parent MZM 120. I (t)=±V π The output points are shown as signal points 326, 330 in the phase diagram 320, and a DPSK signal is generated at the output of the sub-MZM 130. Similarly, the ±1 in the field is related to the data modulation φ Q (t) corresponds to a 0 or π degree phase shift in the modulated optical E field at the output of the quadrature or second arm 114 of the parent MZM 120. Q (t)=±V π The output points are represented by signal points 328, 332 in the phase diagram 320, and a DPSK signal is produced at the output of the child MZM 140. The two DPSK optical signals in each arm 112, 114 of the parent MZM 120 are combined at the output. The quadrature bias signal from the bias driver 109 is applied to the arms 112, 114 via the bias electrodes 171, 172. Mathematically, j is multiplied by the field of the quadrature modulated signal. The quadrature bias results in an additional phase difference of Δφ=π / 2, which orthogonalizes the two DPSK signals, producing points of the QPSK constellation, points 334, 336, 338, 340.

[0049] Figure 3BA constellation diagram 350 of a Mach-Zehnder superstructure modulator 100 configured for 4QAM / QPSK operation is shown. Four quadrature-added symbols are shown as points 334, 336, 338, 340. Points 334, 336, 338, 340 each exhibit a spacing of ±0.7 ±0.7j from the origin of the diagram. Depending on the fidelity of the channel through which the symbols are transmitted and received, the received symbols may differ from the ideal positions of points 334, 336, 338, 340. The received signal fidelity is related to the ability of the receive processor to correctly identify the symbol. That is, to identify which of the four constellation points 334, 336, 338, 340 was transmitted. Therefore, the additional spacing between symbols provides additional design margin.

[0050] As described above, the four constellation points allow encoding of two bits per symbol or point 334, 336, 338, 340. Figure 3C Table 300 including truth tables and field and intensity values ​​at the output of a Mach-Zehnder superstructure modulator 100 configured for 4QAM / QPSK operation is shown. Table 300 shows the symbol, phase modulation signal values ​​φ of the I modulator (sub-MZM 130) I (t), the phase modulation signal value φ of the Q modulator (sub-MZM 140) Q (t), the electric field E at the output of the parent MZM 120 , and the intensity I at the output of the parent MZM 120 .

[0051] The value I=1.0 in table 300 indicates a 3 dB inherent loss from the quadrature bias of the parent MZM 120. This is a manifestation of the fact that the in-phase modulated signal and the quadrature modulated signal exist simultaneously at the output of the parent MZM 120, independent of time. For each symbol transmitted to the Mach-Zehnder superstructure substrate, the quadrature-add combiner effectively discards half the intensity from the output. Therefore, these known configurations of the MZM superstructure modulator system 100 have an inherent 3 dB modulated optical insertion loss (MOIL).

[0052] Figure 4 An embodiment of an IQ Mach-Zehnder superstructure modulator system 400 of the present teachings is shown. The superstructure modulator system 400 includes a combination of Figure 1 The superstructure modulator system 400 of the present teachings can be used to reduce and / or eliminate the inherent MOIL in the known superstructure modulator system 100 by using an AC bias scheme. The IQ Mach-Zehnder superstructure modulator 400 has a structure for generating an optical signal E in421, the optical signal may be, for example, an optical carrier. The parent MZM 420 includes two arms 412, 414. The optical signal at the input of the parent MZM 420 is split into the two arms 412, 414 of the parent MZM 420 by an optical splitter 408. The optical splitter 408 may be a 50 / 50 splitter, or may have many other split ratios in various embodiments. The first arm 412 includes a daughter MZM 430, and the second arm 414 includes another daughter MZM 440. Each daughter MZM 430, 440 includes a pair of arms 423, 424, 425, 426, which have a corresponding pair of modulation electrodes 431, 432, 441, 442 and a corresponding pair of bias electrodes 451, 452, 461, 462. The modulation electrodes 431, 432, 441, 442 give modulation phases to the optical signals in the corresponding arms 423, 424, 425, 426 in response to the modulation signals. The bias electrodes 451, 452, 461, 462 give bias phases to the optical signals in the corresponding arms 423, 424, 425, 426 in response to the bias signals.

[0053] In some embodiments, the modulation electrodes 431, 432, 441, 442 and the bias electrodes 451, 452, 461, 462 are configured as a differential drive configuration. The modulation electrodes 431, 432, 441, 442 are connected to a modulation driver 404 that provides an RF modulation signal that imparts a modulation phase to the optical signal passing through the arms 423, 424, 425, 426. The bias electrodes 451, 452, 461, 462 are connected to a bias driver 405 that provides a bias signal. The sub-MZMs 430, 440 impart a modulation phase to the optical signal passing through the arms 412, 414 in response to the modulation signal applied to the modulation electrodes 431, 432, 441, 442.

[0054] The optical signals from the two arms 412, 414 of the parent MZM 420 are combined into an output 422 at the combiner 409. The parent MZM 420 has DC bias electrodes 471, 472 connected to the DC bias driver 406 and AC bias electrodes 481, 491 connected to the AC bias driver 407 on each arm 412, 414. The DC bias electrodes 471, 472 and the AC bias electrodes 481, 491 impart corresponding DC bias phases and AC bias phases to the optical signals passing through the corresponding arms 412, 414. The AC bias electrode 481 modulates the optical signal in the arm 412 with a bias signal that can operate at a high rate, and thus acts as a high-speed modulator. The AC bias electrode 491 modulates the optical signal in the arm 414 with a bias signal that can operate at a high rate, and thus acts as a high-speed modulator. This is in contrast to the DC bias electrodes 471, 472 which impart a nominally constant bias phase on each arm 412, 414. Therefore, in some embodiments, the AC bias electrodes 481, 491 are configured differently than the DC bias electrodes 471, 472 to support modulation of high speed signals.

[0055] The controller 402 controls the modulation drivers 404, 405 and the bias drivers 406, 407. The drivers 404, 405, 406, 407 and the controller 402 may be collectively referred to as a control device 403. In various embodiments, the bias drivers 406, 407, the modulation drivers 404, 405 and / or the controller 402 are constructed by one or more circuits. In various embodiments, the circuits may include FPGAs, ASICs, DSPs, ADCs, DACs and / or other discrete circuits, alone or in combination.

[0056] One feature of the present teachings is that both a DC bias signal and an AC bias signal are applied to the parent MZM 420. This allows for a DC bias that is nominally constant over time and an AC bias that varies over time. For example, the AC bias can vary based on the modulation signal. Thus, the AC bias signal can operate at RF frequencies. The AC bias signal rate can track, for example, the data rate and / or symbol rate of the applied RF data modulation signal. In some embodiments, the AC bias signal can vary based on a particular symbol encoded in a constellation of a phase modulated signal. For example, referring back to the combination Figure 3B 350 of a 4QAM modulated signal, in some embodiments, the AC bias signal depends on which point 334, 336, 338, 340 of the constellation the modulated signal is generating. Said another way, and referring back to the combination Figure 3CTable 300 is described, in some embodiments, the AC bias signal depends on which sign of the truth table the modulated signal is applying. As further described below, this feature including an AC bias signal applied via an AC bias electrode to generate and apply a data-dependent AC bias phase on the superstructure MZM can result in reduced MOIL, improved constellation Hamming distance, and / or improved linearity of the superstructure MZM 400, and represents a significant improvement over the prior art.

[0057] The modulation signal is fed to each modulation electrode 431, 432, 441, 442. The signal is provided by the driver 404 and selected by the controller 402. The corresponding modulation signal corresponds to the I and Q data streams provided from the data feed source, such as a programmable controller (not shown) or other source. As selected by the controller 402 and provided by the drivers 405, 406, 407, the corresponding bias signal is fed to some or all of the bias electrodes 451, 452, 461, 462, 471, 472, 481, 491. The lookup table associated with the controller 402 can be used to store any or all data-related AC bias and / or DC bias values ​​for generating bias signals for the various bias electrodes described herein. In some embodiments, the electrodes can be driven directly by a high-speed digital-to-analog converter.

[0058] In some embodiments, the DC bias signal is configured by the controller 402 to bias the sub-MZM 430 in the first arm 412 at a minimum transmission point and to bias the sub-MZM 440 in the second arm 414 at a minimum transmission point. In some embodiments, the controller 402 configures the driver 404 so that the RF modulated signals of both sub-modulators 430, 440 provide ±V π The differential voltage, which results in a 2V π In some embodiments, the RF modulation signals of both sub-modulators 430, 440 are configured to provide ±V π / 2, which results in a 1V differential voltage for each sub-MZM 430, 440 π Peak-to-peak voltage swing.

[0059] In one embodiment according to the present teachings, the sub-MZM 430 modulation electrodes 431, 432 are differential RF electrodes for in-phase data modulation. The sub-MZM 440 electrodes 441, 442 are differential RF electrodes for quadrature data modulation. The bias electrodes 451, 452 are differential in-phase DC bias electrodes for the sub-MZM 430. The bias electrodes 461, 462 are differential quadrature DC bias electrodes for the sub-MZM 440. The DC bias electrodes 471, 472 are differential DC bias electrodes for the parent MZM 420. In addition, the AC bias electrodes 481, 491 are complementary RF electrodes that are used to modulate the data-dependent phase shift of the AC bias of the parent MZM 420.

[0060] In some embodiments, in addition to a fixed, time-independent DC bias phase shift Δφ=π / 2, the AC bias causes part of the quadrature phase shift of the parent MZM 420 to include a data modulation-related phase shift This is similar to the concept of applying an AC signal on a DC signal. By analogy, the root mean square (rms) value of this AC modulation applied at a quadrature phase bias Δφ=π / 2 is what reduces the insertion loss to less than 3dB or eliminates the insertion loss completely (0dB). This is achieved because the varying bias results in the in-phase addition of the in-phase optical signal and the quadrature optical signal generated by the sub-MZM 430 and the sub-MZM 440, respectively, which is also referred to as coherent addition. This is in contrast to known superstructure modulators, which rely on conventional quadrature addition provided only by a Δφ=π / 2 DC bias, which is an incoherent addition of the I and Q signals. The AC bias on the parent modulator 420 of the IQ Mach-Zehnder superstructure modulator system 400 of the present teaching can provide up to 3dB of MOIL reduction compared to an IQ Mach-Zehnder superstructure modulator system in which no AC bias is applied to the parent modulator.

[0061] Although described in conjunction with the differential drive configuration Figure 4 Although the embodiments of the present invention are discussed in conjunction with the embodiment of the present invention, those skilled in the art will appreciate that many other drive configurations and electrode configurations may be used. For example, a single electrode modulation scheme and / or a single electrode bias configuration may also be used for any or all of the sub-MZMs 430, 440 and the parent MZM 420.

[0062] Figure 5A Table 500 is shown including a symbol truth table, DC and AC bias phases, and field and intensity values ​​at the output for an embodiment of a Mach-Zehnder superstructure modulator configured for 4QAM operation according to the present teachings. Table 500 shows an applied 2V π Modulation voltage method. Such a table can be combined with e.g. Figure 4The described embodiment of the IQ Mach-Zehnder superstructure modulator system 400 is associated with a configuration in which the sub-MZMs 430, 440 are biased at minimum transmission and the applied peak-to-peak modulation signal voltage is 2V. π .

[0063] The mathematical description of the operation is as follows. In the proposed scheme, as shown in Table 500, each symbol of the applied modulation is associated with an applied phase value The applied phase value is associated with the applied modulation phase ΔΦ for the in-phase modulator 430. I (t) and the applied modulation phase ΔΦ for the quadrature modulator 440 Q The output field of the modulator system 400 can be described by the following equation:

[0064]

[0065]

[0066] in And among them Corresponds to the logical XOR operation. In addition, in order to obtain The average value, every hour, And every time hour, Table 500 presents the complex field E and intensity I = |E| for each symbol in the 4QAM constellation. 2 .

[0067] Figure 5B A phase diagram 520 is shown representing output signal points of an embodiment of a Mach-Zehnder superstructure modulator configured for 4QAM operation according to the present teachings and a known 4QAM configured Mach-Zehnder superstructure modulator. The phase diagram 520 shows an applied 2V π Peak-to-peak modulation voltage method. Refer to the combination Figure 5A Table 500 and combination of description Figure 5B In both phase diagrams 520 depicted, vectors 501, 502 each represent a corresponding path for symbol "0", where vector 501 is an in-phase vector and vector 502 is an orthogonal vector. Following the row for symbol "00", in-phase vector 501 obtains a positive 45° phase angle 540 as shown. The AC bias phase shift, and the orthogonal vector 502 is shown by the negative 45° phase angle 541 The AC bias phase shifts the phase. These vectors are then added "in phase" to produce the symbol as point 510 with E = l + j. This is in contrast to the orthogonal addition caused by no applied AC bias, which results in symbol 340 with E = 0.7 + 0.7j combined with Figure 3A The examples presented are similar. The AC bias phases for other symbols in the constellation provided in the table 500 described in conjunction with FIG. 5 are also shown. The phase rotation of the output of the child MZM 430, 440 is data dependent at the combiner of the parent MZM 420 because different applied symbols result in different biases applied to the electrodes 481, 491 and associated different phase shifts in each arm 412, 414 of the parent MZM 420.

[0068] Figure 5C A constellation diagram 560 is shown representing the modulated output signals of an embodiment of a Mach-Zehnder superstructure modulator configured for 4QAM operation according to the present teachings and a known 4QAM configured Mach-Zehnder superstructure modulator. The phase diagram 520 shows the applied 2V π Peak-Swing Modulation Voltage Implementation. Clearly, the resulting points 510, 511, 512, 513 representing the output of the Mach-Zehnder superstructure modulator of the present teachings have a higher amplitude transmission than the corresponding points 334, 336, 338, 340 for the known superstructure modulator. The theoretically calculated MOIL improvement is 3.01 dB. Simulations of the resulting MOIL produce the same value. The in-phase addition symbol points 510, 511, 512, 513 each exhibit a separation of ±1.0 ±1.0j from the origin of the figure. This increase in separation improves the signal strength to more robustly pass through the channel. This increase in separation improves the ability of a coherent receiver to decode and correctly identify the transmitted symbols. In addition, the in-phase addition of the orthogonal signals reduces the insertion loss associated with the modulator.

[0069] One feature of the method and apparatus of the present teachings is that they can be applied to many phase-based modulation schemes produced by MZM superstructure modulators. This includes the QPSK and 4QAM formats described above. This also includes, for example, various nQAM modulation formats, and the value n can take many values ​​including, for example, n=4, 8, 16, 64, 256, etc. The modulated optical signal from the Mach-Zehnder superstructure modulator of the present teachings can carry information, for example, by means of symbols selected from a set of at least two, four or more different symbols.

[0070] An aspect of the present teachings is that, in some embodiments, certain advantages can be achieved when an AC bias phase is used in a two-dimensional complex plane (IQ) to rotate the in-phase and quadrature components of an nQAM signal by complementary data-dependent phase angles.

[0071] As follows FIG. 6A to FIG. 6C As described in the associated description, combined Figure 4 The described super structure modulator 400 can also be used to generate even higher order signal constellations such as 16QAM and 64QAM, and / or generate nQAM signals with high linearity and reduced MOIL. The system and method of the present teaching thus relaxes the requirement of using a nonlinear signal constellation analyzer as the last signal processing block on the receiving side digital signal processor to perform decision operations on the received symbols and perform symbol-to-bit mapping operations. These features can significantly reduce the cost, complexity and / or size, weight and power consumption of the receiver.

[0072] Fig. 6A The present teaching is configured for use with a 1V π Constellation diagram 600 of modulated output signals of an embodiment of a 16QAM operated Mach-Zehnder superstructure modulator and a known 16QAM configured Mach-Zehnder superstructure modulator driving an operating point. Fig. 6A The improvement is shown for 16QAM simulations where for 1V π In this case, the insertion loss can be calculated by calculating 9.0 / 5.0=1.8 and using the formula 10*log10(1.8)=2.55dB (theoretical) and 2.61dB (simulated). This corresponds to a 2.61dB MOIL improvement compared to the 8.55dB MOIL. The 8.55dB MOIL includes the 3dB caused by the orthogonal addition, the 1V π +3dB due to underdriving and +2.55dB due to the peak-to-average ratio of the PAM4 signal.

[0073] Figure 6B The present teaching is configured for use with a 2V π Constellation diagrams of modulated output signals of an embodiment of a driven 16QAM operated Mach-Zehnder superstructure modulator and a known 16QAM configured Mach-Zehnder superstructure modulator. Figure 6B The improvement is shown for 16QAM simulations where for 2V π In this case, the insertion loss can be calculated by calculating 9.0 / 5.0=1.8 and 3dB+10*log10(1.8)=5.55dB (theoretical) and 5.79dB (in simulation). This again corresponds to a 5.79dB MOIL improvement compared to a 5.55dB MIOL. However, the 1QAM constellation is slightly distorted when the 16QAM constellation points do not have equal Hamming distances.

[0074] Figure 6C The present teaching is configured for use with a 2V πConstellation diagrams of modulated output signals of embodiments of a driven and linearized 16QAM operated Mach-Zehnder superstructure modulator and a known 16QAM configured Mach-Zehnder superstructure modulator. In the case where the signal constellation points have an equal Hamming distance of 2, a more linear signal constellation can be generated. This linearity improvement can, for example, improve receiver sensitivity and / or make the system more tolerant to losses and noise. This configuration produces a 5.53dB reduction in MOIL compared to a theoretical 5.55dB MOIL. In other words, we have recovered most of the lost signal power at the transmitter associated with prior art amplitude and / or phase based optical modulators. For some applications, a small increase in MOIL is well worth the associated improvement in linearity. FIG. 6A to FIG. 6C Indicating that symbols for the in-phase addition case have maximum power transmission may be an advantage over other 16QAM modulation schemes.

[0075] The data-dependent phase shift of the AC bias for 4QAM or QPSK implementations can be implemented as exactly equal and opposite configurations. Since equal and opposite bias phases are applied to the mother MZM 420, the sum is The two arms 412, 414 of the AC bias signal are coupled to each other, and although the RF drive signals are complementary, this bias condition can still be referred to as a differential AC bias drive configuration. However, in general, for each arm 412, 414, the data-related AC bias phase does not necessarily have the same amplitude. Instead, in some embodiments, particularly those with larger constellations, the AC bias phase is used as a complementary phase bias. That is, the applied AC bias phase totals 90°, so that an AC bias phase of X° is applied to one arm 412, and 90-X° is applied to the other arm 414. This is the case for signals that fall in the 0-90° quadrant of the phase diagram. The effect of the additional phase from the AC bias is to move the vector associated with the in-phase component of the desired symbol point and the vector associated with the orthogonal component of the desired symbol point toward each other so that they add constructively "in phase". Note that the differential AC bias drive of a 4QAM or QPSK implementation is a special case of complementary phase biases with equal amplitudes.

[0076] Thus, for some embodiments such as QPSK or 4QAM, for all four symbols, a complementary phase shift of π / 4 may be selected so that the total path phase shifts for all four paths are equal. That is, the magnitude of the applied phase offsets is of the same magnitude. In various other embodiments, particularly those with larger constellation sizes, the magnitudes of the applied phase offsets are not all of the same magnitude. As the number of symbols increases, the applied bias phases typically increase in magnitude. In practice, these applied biases may be predetermined and provided in a lookup table accessed by the control device 403.

[0077] Fig. 7A A phase diagram 700 is shown for a 16QAM constellation. Figure 7B Shown and represented with Fig. 7A 700 and associated phase and amplitude of the transmitted optical carrier. Referring to both figures, a symbol point 702 includes a corresponding vector 704 having an amplitude and a phase angle 706. The amplitudes and phase angles 706, 712, 714 of the vectors 704, 708, 710, 716 shown indicate that there are three phase angles 706, 712, 714 in each quadrant, such as three phase angles 706, 712, 714 for the 0 to 90 degree quadrant. Vector 710 and vector 716 have the same 45 degree phase angle 712. The points at the ends of the vectors 704, 708, 710, 716 represent the four symbols 752 shown in the table 750. For each of the four symbols 752 indicated in the table 750, a complementary AC bias phase to be applied to each electrode 481, 491 can be determined for each signal point, such as point 702. In some implementations, the complementary phase based on the predetermined symbol may be stored in a lookup table that may be accessed by the control device 403 .

[0078] One feature of the present teachings is that they can be applied to dual polarization multiplexed IQ Mach-Zehnder modulators. Such modulators can advantageously provide twice the data capacity per optical carrier compared to single polarization modulators.

[0079] Figure 8 1 shows an embodiment of a dual polarization IQ Mach-Zehnder superstructure modulator system 800 of the present teachings. The dual polarization IQ Mach-Zehnder superstructure 802 includes two IQ Mach-Zehnder superstructure modulators 804, 806, one in each arm of the dual polarization IQ Mach-Zehnder superstructure 802. For example, these IQ Mach-Zehnder superstructure modulators 804, 806 may be combined Figure 4Each IQ Mach-Zehnder superstructure modulator 804, 806 is provided with a modulation signal and a bias signal by a corresponding control device 808, 810, which can be combined with Figure 4 The control device 403 is the same or similar to the description. The input optical carrier is separated to provide an optical signal to each of the IQ Mach-Zehnder superstructure modulators 804, 806 in each arm of the dual polarization Mach-Zehnder superstructure 802. In various embodiments, each IQ Mach-Zehnder superstructure modulator 804, 806 generates a modulated optical signal by applying an AC bias to one or both of the superstructure modulators 804, 806, the modulated optical signal having a reduced MOIL and / or improved linearization and / or improved Hamming distance as described herein. For example, this can be any of DPSK, QPSK, 8QAM, 16QAM, 64QAM or other phase modulated optical signals. A polarization rotator is used to rotate the signal output from the IQ Mach-Zehnder superstructure modulator 806 to construct an output signal including modulated optical signals in two orthogonal polarizations at the output of the dual polarization IQ Mach-Zehnder superstructure 802. This is sometimes referred to as a polarization multiplexed optical signal or a dual polarization optical signal.

[0080] The systems and methods of the present teachings can be applied to MZMs made using any of a variety of known materials. For example, lithium niobate, indium phosphide, gallium arsenide, and / or silicon photonics technology can be used to construct the MZM modulators of the present teachings. Some embodiments of the MZM superstructure in-phase and quadrature-phase optical modulators can additionally include two sub-MZMs. Due to, for example, quadrature addition losses, peak-to-average power ratio losses of the electrically driven pulse amplitude modulation signal, and / or losses caused by under-driven sub-MZMs generating nQAM signals, the embodiments described herein can simultaneously improve linearity and reduce MOIL.

[0081] Some embodiments of the systems and methods of the present teachings include electrically driving two high-speed phase modulators that rotate the in-phase and quadrature components of an nQAM signal in the complex plane (IQ) by data-related phase angles that are complementary to each other. In addition, some embodiments may implement the algorithms described herein to calculate the two complementary phase angles for nQAM signal generation that allows for 2V π The peak-to-peak voltage swing is 1V π With 2V πThe voltage swing between the two is used to electrically drive the in-phase quadrature MZM. Alternatively or additionally, some embodiments of the systems and methods of the present teachings construct a lookup table that stores the phase angle associated with the dual complementary data on the transmission side, and the lookup table can be accessed by a digital signal processor that uses two high-speed digital-to-analog converters to generate the phase angle associated with the data at the baud rate.

[0082] Equivalent solution

[0083] Although the applicant's teachings are described in conjunction with various embodiments, it is not intended that the applicant's teachings be limited to such embodiments. On the contrary, as will be appreciated by those skilled in the art, the applicant's teachings include various alternatives, modifications, and equivalents that can be made without departing from the spirit and scope of the present teachings.

[0084] In addition, the present teaching also includes the following embodiments.

[0085] (1) An optical Mach-Zehnder superstructure modulator, comprising:

[0086] a) an optical splitter having an input end configured to receive an input optical signal, the optical splitter splitting the received input optical signal to provide a first optical signal to a first optical path and a second optical signal to a second optical path;

[0087] b) a first sub-Mach-Zehnder modulator optically coupled to the first optical path, the first sub-Mach-Zehnder modulator imparting a modulation phase on the first optical signal in response to a first modulation signal;

[0088] c) a first high-speed optical modulator optically coupled to the first optical path, the first high-speed optical modulator imparting a first AC bias phase on the first optical signal in response to a first AC bias signal;

[0089] d) a second sub-Mach-Zehnder modulator optically coupled to the second optical path, the second sub-Mach-Zehnder modulator imparting a modulation phase on the second optical signal in response to a second modulation signal;

[0090] e) a second high speed modulator optically coupled to the second optical path, the second high speed modulator imparting a second AC bias phase on the second optical signal in response to a second AC bias signal;

[0091] f) an optical combiner having a first input end optically coupled to the first optical path and a second input end optically coupled to the second optical path, the optical combiner combining the first optical signal and the second optical signal to provide an output optical signal at an output;

[0092] g) at least one driver that provides the first modulation signal to the first sub-Mach-Zehnder modulator, provides the second modulation signal to the second sub-Mach-Zehnder modulator, provides the first AC bias signal to the first high speed modulator, and provides the second AC bias signal to the second high speed modulator, wherein the at least one driver is configured such that at least one of the first AC bias signal and the second AC bias signal is a function of at least one of the first modulation signal and the second modulation signal.

[0093] (2) The optical Mach-Zehnder superstructure modulator of (1), wherein the at least one driver is configured such that the first AC bias phase and the second AC bias phase include complementary phase angles.

[0094] (3) The optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured such that at least one of the first AC bias phase and the second AC bias phase includes The other AC bias phase of the first AC bias phase and the second AC bias phase includes The bias phase.

[0095] (4) The optical Mach-Zehnder superstructure modulator according to (1), wherein the optical Mach-Zehnder superstructure modulator is configured at a quadrature bias point.

[0096] (5) The optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured such that at least one of the first modulation signal and the second modulation signal comprises a phase shift keying modulation signal.

[0097] (6) The optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured such that at least one of the first modulation signal and the second modulation signal comprises an in-phase phase shift keying modulation signal.

[0098] (7) The optical Mach-Zehnder superstructure modulator according to (6), wherein the at least one driver is configured such that the other modulation signal of the first modulation signal and the second modulation signal comprises an orthogonal phase shift keying modulation signal.

[0099] (8) The optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured such that at least one of the first modulation signal and the second modulation signal comprises an amplitude modulation signal.

[0100] (9) The optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured such that at least one of the first modulation signal and the second modulation signal comprises an in-phase amplitude modulation signal.

[0101] (10) The optical Mach-Zehnder superstructure modulator according to (9), wherein the at least one driver is configured such that the other modulation signal of the first modulation signal and the second modulation signal comprises an orthogonal phase amplitude modulation signal.

[0102] (11) The optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured so that at least one of the first modulation signal and the second modulation signal includes V π The peak-to-peak voltage swing.

[0103] (12) The optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured so that at least one of the first modulation signal and the second modulation signal includes 2V π The peak-to-peak voltage swing.

[0104] (13). An optical Mach-Zehnder superstructure modulator according to (1), wherein at least one of the first high-speed optical modulator and the second high-speed optical modulator includes an electrode, and the electrode is configured to impart at least one of the first AC bias phase and the second AC bias phase to at least one of the first optical signal and the second optical signal.

[0105] (14). An optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured to cause at least one of the first AC bias signal and the second AC bias signal to change based on a specific symbol encoded in at least one of the first modulation signal and the second modulation signal.

[0106] (15). An optical Mach-Zehnder optical superstructure modulator according to (1), wherein the at least one driver is configured such that at least one of the first AC bias signal and the second AC bias signal is selected to provide a desired modulated light insertion loss (MOIL) of the optical Mach-Zehnder superstructure modulator.

[0107] (16). An optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured such that at least one of the first AC bias signal and the second AC bias signal is selected to provide a reduction in modulated light insertion loss (MOIL) of the optical Mach-Zehnder superstructure modulator.

[0108] (17) The optical Mach-Zehnder superstructure modulator according to (16), wherein the reduction in the modulated light insertion loss (MOIL) of the optical Mach-Zehnder superstructure modulator comprises a 3 dB reduction in the modulated light insertion loss (MOIL).

[0109] (18). An optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured such that at least one of the first AC bias signal and the second AC bias signal is selected to provide a desired linearity of the output optical signal.

[0110] (19). An optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured such that at least one of the first AC bias signal and the second AC bias signal is selected to provide a desired Hamming distance of the output optical signal.

[0111] (20) The optical Mach-Zehnder superstructure modulator of (1), wherein the at least one driver comprises a lookup table storing phase angles associated with data.

[0112] (21). An optical Mach-Zehnder superstructure modulator according to (1), wherein the optical Mach-Zehnder superstructure modulator is constructed using at least one of lithium niobate, indium phosphide, gallium arsenide or silicon photonics technology.

[0113] (22). An optical Mach-Zehnder superstructure modulator according to (1), wherein the at least one driver is configured so that the output optical signal includes at least one of a DPSK, QPSK, 4QAM, 8QAM, 16QAM or 64QAM optical signal.

[0114] (23). The optical Mach-Zehnder superstructure modulator according to (1) further includes a second optical Mach-Zehnder superstructure modulator configured in parallel with the optical Mach-Zehnder superstructure modulator, wherein the output of the optical Mach-Zehnder superstructure modulator and the output of the second optical Mach-Zehnder superstructure modulator are combined by a combiner to generate a polarization multiplexed optical signal.

[0115] (24). A method for modulating an optical Mach-Zehnder superstructure modulator, the method comprising:

[0116] a) applying a first modulation signal to a first sub-Mach-Zehnder interferometric modulator in a first arm of the optical Mach-Zehnder superstructure modulator to impart a first modulation phase on a first optical signal;

[0117] b) applying a second modulation signal to a second sub-Mach-Zehnder interferometric modulator located in a second arm of the optical Mach-Zehnder superstructure modulator to impart a second modulation phase on the second optical signal;

[0118] c) phase shifting the first optical signal by applying a first AC bias signal to the first arm of the optical Mach-Zehnder superstructure;

[0119] d) phase shifting the second optical signal by applying a second AC bias signal to the second arm of the optical Mach-Zehnder superstructure; and

[0120] e) interferometrically combining the first optical signal and the second optical signal to generate an output optical signal at an output,

[0121] At least one of the first AC bias signal and the second AC bias signal is a function of at least one of the first modulation signal and the second modulation signal.

[0122] (25) The method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein the phase shift angle on the first optical signal and the phase shift angle on the second optical signal are complementary angles.

[0123] (26) The method for modulating an optical Mach-Zehnder superstructure modulator according to (24), further comprising biasing the optical Mach-Zehnder superstructure modulator to an orthogonal bias point.

[0124] (27) A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein applying the first modulation signal to the first sub-Mach-Zehnder interferometric modulator includes applying a phase shift keying modulation signal.

[0125] (28) A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein applying the first modulation signal to the first sub-Mach-Zehnder interferometric modulator includes applying an in-phase phase shift keying modulation signal.

[0126] (29). A method for modulating an optical Mach-Zehnder superstructure modulator according to (28), wherein applying the second modulation signal to the second sub-Mach-Zehnder interferometric modulator includes applying an orthogonal phase shift keying modulation signal.

[0127] (30) The method of modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein applying the first modulation signal to the first sub-Mach-Zehnder interferometer modulator includes applying an amplitude modulation signal.

[0128] (31). A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein applying the first modulation signal to the first sub-Mach-Zehnder interferometer modulator includes applying an in-phase amplitude modulation signal.

[0129] (32) A method for modulating an optical Mach-Zehnder superstructure modulator according to (31), wherein applying the second modulation signal to the second sub-Mach-Zehnder interferometer modulator includes applying an orthogonal amplitude modulation signal.

[0130] (33) A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein applying the first modulation signal to the first sub-Mach-Zehnder interferometric modulator comprises applying V π Peak-to-peak voltage swing.

[0131] (34) A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein applying the first modulation signal to the first sub-Mach-Zehnder interferometric modulator comprises applying 2V π Peak-to-peak voltage swing.

[0132] (35). A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein at least one of the first AC bias signal and the second AC bias signal changes based on a specific symbol encoded in at least one of the first modulation signal and the second modulation signal.

[0133] (36). A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein at least one of the first AC bias signal and the second AC bias signal is selected to provide a desired modulated light insertion loss (MOIL) of the optical Mach-Zehnder superstructure modulator.

[0134] (37). A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein at least one of the first AC bias signal and the second AC bias signal is selected to provide a reduction in modulated light insertion loss (MOIL) of the optical Mach-Zehnder superstructure modulator.

[0135] (38). A method for modulating an optical Mach-Zehnder superstructure modulator according to (37), wherein the reduction in the modulated light insertion loss (MOIL) of the optical Mach-Zehnder superstructure modulator includes a 3dB reduction in the modulated light insertion loss (MOIL).

[0136] (39). A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein at least one of the first AC bias signal and the second AC bias signal is selected to provide a desired linearity of the output optical signal.

[0137] (40) A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein at least one of the first AC bias signal and the second AC bias signal is selected to provide a desired Hamming distance of the output optical signal.

[0138] (41). A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein phase shifting the first optical signal by applying the first AC bias signal to the first arm of the optical Mach-Zehnder superstructure includes querying a lookup table storing a phase angle associated with data.

[0139] (42). A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein the optical Mach-Zehnder superstructure modulator is constructed using at least one of lithium niobate, indium phosphide, gallium arsenide and / or silicon photonics technology.

[0140] (43) A method for modulating an optical Mach-Zehnder superstructure modulator according to (24), wherein the output optical signal comprises at least one of DPSK, QPSK, 8QAM, 16QAM and 64QAM optical signals.

[0141] (44) The method for modulating an optical Mach-Zehnder superstructure modulator according to (24), further comprising performing polarization multiplexing on the output optical signal.

Claims

1. An optical Mach-Zehnder superstructure modulator, comprising: a) an optical splitter having an input end configured to receive an input optical signal, the optical splitter splitting the received input optical signal to provide a first optical signal to a first optical path and a second optical signal to a second optical path; b) a first sub-Mach-Zehnder modulator MZM, which is optically coupled to the first optical path, and the first sub-Mach-Zehnder modulator imparts a first modulation phase to the first optical signal in response to a first modulation signal to generate a first modulated phase optical signal; c) a first high-speed optical modulator optically coupled to the first sub-MZM, the first high-speed optical modulator being configured to phase-shift the first modulated phase optical signal from the first sub-MZM by a first AC bias phase in response to a first AC bias signal to generate a first AC phase bias optical signal; d) a second Mach-Zehnder sub-modulator MZM, which is optically coupled to the second optical path, and the second Mach-Zehnder sub-modulator imparts a second modulation phase to the second optical signal in response to a second modulation signal to generate a second modulated phase optical signal; e) a second high-speed optical modulator optically coupled to the second sub-MZM, the second high-speed optical modulator being configured to phase-shift the second modulated phase optical signal from the second sub-MZM by a second AC bias phase in response to a second AC bias signal to generate a second AC phase bias optical signal; f) an optical combiner having a first input optically coupled to the first high-speed optical modulator and a second input optically coupled to the second high-speed optical modulator, the optical combiner combining the first AC phase-biased optical signal and the second AC phase-biased optical signal from the first high-speed optical modulator and the second high-speed optical modulator to provide an output optical signal at an output; as well as g) at least one driver that provides the first modulation signal to the first sub-MZM, provides the second modulation signal to the second sub-MZM, provides the first AC bias signal to the first high-speed optical modulator, and provides the second AC bias signal to the second high-speed optical modulator, wherein the at least one driver is configured to cause at least one of the first AC bias signal and the second AC bias signal to change as at least one of the first modulation signal and the second modulation signal changes.

2. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that the first AC bias phase and the second AC bias phase include complementary phase angles.

3. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first AC bias phase and the second AC bias phase includes The other AC bias phase of the first AC bias phase and the second AC bias phase includes The bias phase.

4. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The optical Mach-Zehnder superstructure modulator is configured at quadrature bias points.

5. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first modulation signal and the second modulation signal comprises a phase shift keying modulation signal.

6. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first modulation signal and the second modulation signal comprises an in-phase phase shift keying modulation signal.

7. The optical Mach-Zehnder superstructure modulator according to claim 6, wherein: The at least one driver is configured such that the other of the first modulation signal and the second modulation signal comprises a quadrature phase shift keying modulation signal.

8. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first modulation signal and the second modulation signal comprises an amplitude modulation signal.

9. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first modulation signal and the second modulation signal comprises an in-phase amplitude modulation signal.

10. The optical Mach-Zehnder superstructure modulator according to claim 9, wherein: The at least one driver is configured such that the other of the first modulation signal and the second modulation signal comprises a quadrature phase amplitude modulation signal.

11. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first modulation signal and the second modulation signal includes V π The peak-to-peak voltage swing.

12. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first modulation signal and the second modulation signal includes a 2V π The peak-to-peak voltage swing.

13. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: At least one of the first and second high-speed optical modulators includes an electrode configured to impart at least one of the first and second AC bias phases on at least one of the first and second modulated phase optical signals.

14. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured to cause at least one of the first and second AC bias signals to change based on a specific symbol encoded in at least one of the first and second modulation signals.

15. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first AC bias signal and the second AC bias signal is selected to provide a desired modulated light insertion loss (MOIL) of the optical Mach-Zehnder superstructure modulator.

16. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first AC bias signal and the second AC bias signal is selected to provide a reduction in a modulated light insertion loss (MOIL) of the optical Mach-Zehnder superstructure modulator.

17. The optical Mach-Zehnder superstructure modulator according to claim 16, wherein: The reduction in modulated light insertion loss (MOIL) of the optical Mach-Zehnder superstructure modulator includes a 3 dB reduction in the modulated light insertion loss (MOIL).

18. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first AC bias signal and the second AC bias signal is selected to provide a desired linearity of the output optical signal.

19. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that at least one of the first AC bias signal and the second AC bias signal is selected to provide a desired Hamming distance of the output optical signal.

20. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver includes a lookup table storing phase angles associated with data.

21. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The optical Mach-Zehnder superstructure modulator is constructed using at least one of lithium niobate, indium phosphide, gallium arsenide, or silicon photonics technology.

22. The optical Mach-Zehnder superstructure modulator according to claim 1, wherein: The at least one driver is configured such that the output optical signal comprises at least one of a DPSK, QPSK, 4QAM, 8QAM, 16QAM, or 64QAM optical signal.

23. The optical Mach-Zehnder superstructure modulator according to claim 1, further comprising a second optical Mach-Zehnder superstructure modulator arranged in parallel with the optical Mach-Zehnder superstructure modulator, wherein: The output of the optical Mach-Zehnder superstructure modulator and the output of the second optical Mach-Zehnder superstructure modulator are combined through a combiner to generate a polarization multiplexed optical signal.

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