KR100993843B1 - Versatile compact transmitter for generation of advanced modulation formats - Google Patents

Abstract

The present invention provides a driver having an N-level digital multilevel transformer (DMT) configured to receive a two-level digital electrical signal representing ones and zeros and output an N (where N > 2) level electrical signal; An FM source configured to receive the output N-level electrical signal and generate an optical frequency modulated signal, and an optical spectrum configured to receive the optical frequency modulated signal output by the FM source and generate a predetermined RZ-DPSK optical signal An optical signal generation system of a zero return differential phase shift method (RZ-DPSK) having an optical spectrum reshaper (OSR). In another aspect, the present invention (1) receiving a two-level digital electrical signal representing the (1) and 0 and outputs an N (where N> 2) level electrical signal, (2) receiving the output N-level electrical signal Generating an optical frequency modulated signal, and (3) generating an optical zero-differential phase shift keying (RZ-DPSK) optical signal including the step of receiving the optical frequency modulated signal and generating a predetermined RZ-DPSK optical signal. It is about a method.

Zero Return Differential Phase Shift Mode (RZ-DPSK) optical signal generation system, FM source, N level digital multilevel transformer, optical spectrum reshaper,

Description

VERSATILE COMPACT TRANSMITTER FOR GENERATION OF ADVANCED MODULATION FORMATS}

References to pending patent applications pending

This patent application

(Iii) pending US patent application No. 8, filed November 8, 2005, by Daniel Mahgerefteh et al, entitled POWER SOURCE FOR A DISPERSION COMPENSATION FIBER OPTIC SYSTEM. Partially filed Application No. 11 / 272,100 (agent document number TAYE-59474-00006 CON);

(Ii) Partial application of pending prior US patent application 10 / 308,522 filed December 3, 2002 by Daniel McGerefte et al. Under the title HIGH-SPEED TRANSMISSION SYSTEM COMPRISING A COUPLED MULTI-CAVITY OPTICAL DISCRIMINATOR. TAYE-59474-00007);

(V) Partial application of pending US patent application Ser. No. 11 / 441,944, filed on May 26, 2006, by Daniel McGerefte et al. Under FLAT DISPERSION FREQUENCY DISCRIMINATOR (FDFD) (Representative Document No. TAYE-59474-00009 CON );

(V) Partial application of pending US patent application Ser. No. 11 / 068,032, filed on February 28, 2005, by Daniel McGeraffe, et al., Titled OPTICAL SYSTEM COMPRISING AN FM SOURCE AND A SPECTRAL RESHAPING ELEMENT. 31);

(Iv) pending application of pending US patent application Ser. No. 11 / 084,630, filed March 18, 2005, by Daniel McGerefte et al. Under the title FLAT-TOPPED CHIRP INDUCED BY OPTICAL FILTER EDGE (agent DOC-TAYE-34);

(V) Partial pending US patent application 11 / 702,436, filed on February 5, 2007 by Kevin McCallion et al, entitled MULTI-RING RESONATOR IMPLEMENTATION OF OPTICAL SPECTRUM RESHAPER FOR CHIRP MANAGED LASER TECHNOLOGY. Continuing application (agent document number TAYE-23 RR CON);

(V) Partial pending application of US Patent Application No. 11 / 084,633, filed March 18, 2005, by Daniel McGeraffe, et al., Entitled METHOD AND APPARATUS FOR TRANSMITTING A SIGNAL USING SIMULTANEOUS FM AND AM MODULATION. -33);

(Ⅷ) SPECIAL RESPONSE MODIFICATION VIA SPATIAL FILTERING WITH OPTICAL FIBER Pending US Patent Application No. 60 / 853,867, filed on October 24, 2006, by Kevin McCallion et al. (Representative Document No. TAYE-47B PROV) ; And

(V) Partial pending application of pending US patent application 60 / 789,863, filed April 6, 2006, by Daniel McGeraffe, et al., On the title of VERSATILE COMPACT TRANSMITTER FOR GENERATION OF ADVANCED MODULATION FORMATS (representative document number TAYE-73 PROV) to be.

The nine patent applications are incorporated herein by reference.

The present invention relates generally to signal transmission and, more particularly, to optical signal transmission.

The quality and performance of a digital fiber optic transmitter is determined by the distance that the transmitted digital signal can propagate without serious distortion. Bit error rate of the signal (BER) is measured after propagation through a dispersive optical fiber, the light output is determined necessary to achieve a given BER, typically ^10-12, which is sometimes called the sensitivity. The difference between the sensitivity at the output of the transmitter and the sensitivity after propagation is sometimes referred to as the dispersion penalty. This is typically characterized by the distance that the dispersion penalty reaches ~ 1 dB. A standard 10Gb / s optical digital transmitter can transmit at distances of ~ 50km before the dispersion penalty, sometimes called dispersion limit, reaches ~ 1dB on a standard singlemode fiber at 1550nm. The variance limit is based on the basic assumption that the digital signal is limited to conversion, i.e. there is no time-varying phase at which the signal crosses the bits, and a bit period of 100 ps, or 1 / (bit rate), for a standard 10 Gb / s transmission. Determined by Another measure of the quality of the transmitter is its absolute sensitivity after fiber propagation.

Three types of fiber optic transmitters are currently known as prior art fiber systems: (i) directly modulated lasers (DML), (ii) Electroabsorption Modulated Lasers (EML), and (i) externally modulated Mach. Gender (Externally Modulated Mach Zhender). For transmission on standard singlemode fiber at 10 Gb / s and 1550 nm, it has generally been considered that MZ modulators and EMLs can reach the longest distance, typically 80 km. Sometimes using a special coding scheme called phase-shaped duobinary, the MZ transmitter can reach 200 km. Direct modulation lasers (DMLs), on the other hand, typically reach less than 5 km because of the DML's inherent time-dependent chirp, which results in severe signal distortion after this distance.

For example, a variety of systems are available for long-range optical wave data transmission (over 80 km at 10 Gb / s) over an optical fiber that increases the DML's reach to more than 80 km at 10 Gb / s in single-mode fiber. United States Patent Application No. 8, filed November 8, 2005, by Daniel Mahgerefteh et al, entitled COMPENSATION FIBER OPTIC SYSTEM. 11 / 272,100 (Agent Document No. TAYE-59474-00006 CON); (Ii) United States Patent Application No. 11 / 441,944 filed May 26, 2006 by Daniel McGerlevte et al. Under the heading FLAT DISPERSION FREQUENCY DISCRIMINATOR (FDFD) (agent document number TAYE-59474-00009 CON); And (iii) United States Patent Application No. 10 / 308,522 filed December 3, 2002 by Daniel McGeraffe, et al. Under the title of HIGH-SPEED TRANSMISSION SYSTEM COMPRISING A COUPLED MULTI-CAVITY OPTICAL DISCRIMINATOR (Attorney Docket No. TAYE-59474-00007). And the references are incorporated herein by reference. Transmitters combined with these new systems are sometimes referred to as Chirp Managed Lasers (CML ^™ ) from Azna LLC of Wilminington, Massachusetts. In this new system, a frequency modulated (FM) source is followed by an Optical Spectrum Reshaper (OSR) that uses frequency modulation to boost the amplitude modulated signal and partially compensate for dispersion in the transmitting fiber. In one embodiment, the frequency modulation source can compensate for a direct modulation laser (DML). An optical spectrum reshaper (OSR), sometimes called a frequency discriminator, can be formed by a suitable optical element, such as a filter, having a wavelength dependent transmission function. OSR may be suitable for converting frequency modulation to amplitude modulation.

In the novel system of the present invention, the chirp characteristics of the frequency modulation source are used and further reformed by configuring the OSR to extend the reach of the CML ^™ transmitter by more than 250 km on standard singlemode fiber of 10 Gb / s and 1550 nm. . The novel system of the present invention is described in US patent application Ser. No. 11 / 068,032 filed on Feb. 28, 2005 by Daniel McGerreft et al under the title OPTICAL SYSTEM COMPRISING AN FM SOURCE AND A SPECTRAL RESHAPING ELEMENT. TAYE-31), (ii) U.S. Patent Application No. 11 / 084,630 filed March 18, 2005, by Daniel McGerefte et al., Titled FLAT-TOPPED CHIRP INDUCED BY OPTICAL FILTER EDGE (Attorney Docket No. TAYE-34), (Current) U.S. Patent Application No. 11 / 702,436 filed February 5, 2007 by Daniel McGerreft et al., Titled MULTI-RING RESONATOR IMPLEMENTATION OF OPTICAL SPECTRUM RESHAPER FOR CHIRP MANAGED LASER TECHNOLOGY. US Patent Application No. 11 / 084,633, filed March 18, 2005, by Kevin McCallion et al, entitled METHOD AND APPARATUS FOR TRANSMITTING A SIGNAL USING SIMULTANEOUS FM AND AM MODULATION. Ki in number TAYE-33) As a combination of selected aspects of the system, the references are incorporated by reference herein.

More specifically, the present invention provides a differentially-phase-shift-keyed (DPSK) return-to-zero (RZ) signal using a chirp management laser of the type described in the patent application described above. It is provided with a generating device.

In still another aspect of the invention, a driver having an N level digital multilevel transformer (DMT) configured to receive a 2 level digital electrical signal representing 1 and 0 and output an N (where N > 2) level electrical signal. And an FM source configured to receive an N-level electrical signal output by the driver and generate an optical frequency modulated signal, and receive an optical frequency modulated signal output by the FM source and generate a predetermined RZ-DPSK optical signal. A zero return differential phase shift keying (RZ-DPSK) optical signal generation system is provided having an optical spectrum reshaper (OSR) configured to operate.

In still another aspect of the present invention, there is provided a method comprising the steps of: (1) receiving a digital electrical signal of two levels representing 1 and 0 and outputting an N (where N > 2) level electrical signal; Receiving a level electrical signal and generating an optical frequency modulated signal; and (3) receiving the optical frequency modulated signal and generating a predetermined RZ-DPSK optical signal. DPSK) optical signal generation method is provided.

These and other objects, features, and advantages of the present invention are considered to be more fully disclosed or apparent when considered in conjunction with the accompanying drawings in which like numerals refer to like parts by the following detailed description of preferred embodiments of the invention.

1 is a schematic diagram of a chirp management laser based RZ-DPSK transmitter of the present invention.

2 shows the bit sequence progression along the transmitter chain in a chirp management laser RZ-DPSK source.

3 shows a DFB laser with a field absorption modulator.

Figure 4 shows the relative spectral position and OSR of the various frequency modulation levels at the three level signal output of the FM source.

DPSK format

In the DPSK format, an input digital electrical signal representing ones and zeros is converted into an electrical signal whose information is encoded in the phase of a continuous wave CW, which is a constant amplitude signal. In this DPSK format, the modulation rule is given that the input random digital sequence of 1 and 0 bits, the phase of the CW signal is converted to π for all 0 bits of generation, while the phase does not change for 1 bits of generation. . As an example, consider the digital sequence of bits shown in Table 1 below and the final DPSK phase that occurred:

TABLE 1

(a) Digital signal: 1 1 1 0 1 0 0 1 0 1 0 0 0 1 1 0 1 0 1 1 0 1 1 ...

(b) Bit phase: 0 0 π π 0 π π 0 0 π 0 π π π 0 0 ...

(c) Bit amplitude: 1 1 -1 -1 1 -1 -1 1 1 -1 1 -1 -1 -1 ...

(d) Bit strength: 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

Here, amplitude refers to a photoelectric field of bits that carry phase information, while intensity refers to intra-bit optical power that does not carry phase information. The photoelectric representation of each bit is complex, while the light intensity is always real positive. The advantage of this modulation format is that it provides a bit error rate like standard on-off keying with a signal-to-noise ratio of less than 3dB, allowing transmission over longer transmission distances over most optical amplifiers. To do it. This is because in the DPSK format all bits carry energy, while in zero return on-off keying (OOK), only one bit has energy and zero bits do not carry energy.

The advantage of DPSK can be realized using a 1 bit delay interferometer in the receiver along with a balanced receiver. The function of the 1-bit delay interferometer is to convert the phase modulation of the DPSK to amplitude modulation. The interferometer has two outputs, an ADD output in which a one-bit delay version of (1) bits is added together and a SUBTRACT output in which a one-bit delay version of (2) bits is subtracted from each other. If the input DPSK signal is branched between two arms of the interferometer, the power in each arm is reduced by a factor of two. The function of an interferometer, which is mainly of the Mach-gender type, is shown below as an example in Table 2: where the amplitude sequence (c) is delayed by one bit in one arm of the Mach-Gender interferometer so that it interferes with the input in the Mach-Gender. Stream (d) to generate ADD (e) and SUBSTRACT (f) outputs. The intensity of these two outputs is not sensitive to the phase of the optical field but is detected by a standard photodetector that measures the light output. The two-port balanced receiver subtracts the detected photocurrent of the ADD and SUBSTRACT ports (g), which is known in the art to have a sensitivity of 3dB higher than a standard OOK transmitter.

TABLE 2

(c) Bit amplitude: 1/2 × 1 1 -1 -1 1 -1 -1 1 1 -1 1 -1 -1 -1

(d) 1-bit delay version: 1/2 × 1 1 -1 -1 1 -1 -1 1 1 -1 1 -1 -1 -1

(e) Amplitude of the ADD port: ... 1 0 1 0 0 1 0 1 0 0 0 1 1 ...

(f) SUBSTRACT port amplitude: ... 0 0 1 0 1 1 0 1 0 1 1 1 0 0

(g) Output of balanced receiver (V) 1 -1 1 -1 -1 1 -1 1 -1 -1 -1 1 1

The bits are identified at the receiver using a digitizer that assigns bit value 1 if the receiver's output V is sometimes above a predetermined voltage value called a decision threshold or 0 if the output voltage V is below the decision threshold. do. As is known in the art, the decision threshold for the DPSK modulation format is set at 0 volts, so that the " distance " between 1 and 0 bits is 2. That is, while the voltage difference between 1 and 0 bits is 1-(-1) = 2, assuming the same average optical power, the voltage difference is 1-0 = 1 for the standard OOK. This two-factor difference is 3dB superior to DPSK because the same bit error rate can be obtained with an optical signal-to-noise ratio (OSNR) of 1/2 as a standard OOK.

In a zero return differential phase shift keying (RZ-DPSK) transmitter, the output of the CW laser is modulated by a sinusoidal clock signal at 30%-50% duty cycle at a selected bit rate (eg 10 GHz) to further improve sensitivity at the receiver. The output intensity is a pulse train of constant intensity at 30% -50% duty cycle at the bit rate, while the phase of the pulse follows the DPSK rule set above.

In the prior art, RZ-DPSK transmitters generally have a CW laser, a first modulator for generating DPSK, and a second modulator with 30% -50% duty cycle pulse or higher sensitivity. Modulators used in the prior art are generally bulky and require high drive voltages (ie> 4-6 V _pp ), thus resulting in undesirably high power dissipation of the Mach-gender phase and / or amplitude modulators. to be.

DPSK and Chirp Management Lasers (CML)

In the present invention, a compact chirp management laser (CML) with an FM source and an optical spectrum reshaper (OSR) is used to generate the RZ-DPSK signal without using an external modulator.

1 shows a schematic diagram of a novel device. A binary electrical digital data stream is provided to a digital multilevel transformer (DMT) that converts two levels of input of the binary electrical data stream to three levels of output according to the procedure described below. The three level digital signal shown in the DMT is used to drive an FM source (eg, a distributed feedback laser, also known as a DFB laser) that converts the input digital three level signal into a three level optical signal. In other words, the output of the DMT is used as input to the CML device. Both the optical frequency and the light intensity of the laser output are modulated in accordance with the three level driver signal output by the DMT.

The amplitude of the electrical signal output by the DMT is selected to produce a prescribed frequency excursion and amplitude excursion to produce a predetermined phase encoding of the DPSK: (i) If zero phase is desired, i.e., amplitude = +1 In this case, the drive amplitude is adjusted such that the chirp at the laser output is Δf = 2 / T, where T is 50 ps for a 50% duty cycle RZ signal at 1/2 time of the bit, eg 10 Gb / s. (Ii) If π phase is desired at the coded DPSK output, i.e., amplitude = -1, then the drive amplitude causes the chirp to generate Δf = 1 / T at the output of the laser. Since the phase shift across zero bits is Δφ = 2πTΔf, for a 50% duty cycle RZ-DPSK signal at 10 Gb / s, the chirp = 20 GHz and the π phase shift (amplitude =-) for a zero phase shift (amplitude = +1) Note that for 1) the chirp = 10 GHz.

The optical output of the FM source is the optical spectrum reshaper (OSR), i.e. (i) the OSR increases the amplitude modulation of the output signal, and (ii) the OSR is capable of reducing the input adiabatic frequency deviation (output by the It is passed through a filter with two functions that converts it into a flat peak chirp with a near instantaneous phase shift near the null output of the signal.

To further illustrate this novel approach, consider the following input binary digital bit sequences at the input to a three-level digital transformer (DMT):

a _n = ... 1 1 1 0 1 0 0 1 0 1 0 0 0 1 1 0 1 0 1 1 0 1 1

Figure 2 illustrates the bit sequence and pulse shape at various points in the transmitter chain (i.e., the transmit phase). The predetermined output sequence b _n , denoted “predetermined output” in FIG. 2, is another binary digital sequence with two values taking +1 and −1. Sequence (b _n) is that remains unchanged while one-bit is generated each time in a _n, while changing from the previous value (b _n-1) while the value of the bit (b _n) 0 bit is generated each time in a _n According to the rule may be associated with the input sequence (a _n ). In conventional RZ-DPSK transmitters, this sequence is generated using another encoder combined with a Mach gender modulator. In the present invention, a differential encoder is no longer needed. For the case of b _n = +1 or -1, this rule can be written as:

(2)

a _n = 1 then b _n = b _n-1

a _n = 0 then b _n = -b _n-1

The sequence a _n enters a three-level digital transformer (DMT) that generates the pulse shape shown in FIG. 2 at point B according to the following rule (in this example, a predetermined output pulse has a 50% duty cycle): If the input bit is a _n = 1, the signal at point B drops to zero (changed by V), holds zero for 50% of the bit time, and then returns to the value V. The voltage drop V is adjusted according to the FM efficiency of the laser to produce a chirp that is twice the bit rate frequency Δf = 1 / T; (Ii) If the input bit is a _n = 0, the output drops to V / 2, maintains this value for a time T and then returns to the value V to generate a chirp with a bit rate frequency, i.e., Δf = 1 / 2T.

This selection of voltage output ensures the generation of an appropriate phase relationship between the bits at the output of the frequency modulated (FM) source as described below. An FM source, such as a DFB laser, is driven by the voltage pattern at point B and produces a frequency and amplitude modulated output waveform shown at point C (frequency profile and phase profile are shown, but amplitude profile is not shown). The value of the drive voltage V is chosen to generate a frequency rate, such as 10 GHz, for the bit rate of the digital signal, i.e. 10 Gb / s data stream with 50% duty cycle. More generally, the complete frequency deviation Δf is chosen such that Δf × T = 1. Where T is the time of the zero return signal, i.e., 1/2 bit period for the 50% duty cycle RZ pulse sequence. The voltage is determined by the FM efficiency (η _FM ) of the source in so-called GHz / V, in other words, by Δf = η _FM V. The phase of the optical signal at the output of the DFB laser is the time integral of the frequency deviation shown in FIG. For example, if a _n = 1 and zero phase is desired, the overall frequency deviation (Δf = 20 GHz) is applied to a 10 Gb / s zero return (RZ) data stream with 50% duty cycle, so that the phase of the frequency modulated signal is 20 GHz x It slips by 2π × 50ps = 2π. When the input bit is a _n = 1, the three-level digital transformer (DMT) generates a half voltage that causes 10 GHz frequency deviation for 10 Gb / s RZ. In this case, the phase of the signal slips by 10 GHz × 2π × 50ps = π, and the last generated adjacent pulses have a π phase shift between them as necessary.

The output of the FM source (laser) goes through an optical spectrum reshaper (OSR), i.e., a filter that raises the amplitude deviation and flattens the chirp as described in the patent application described above for the chirp management laser. As shown in Fig. 2, the strength at the output of the OSR is an RZ-DPSK signal, in which each bit carries the same energy and the data is encoded in the phase of the bit.

The amplitudes of the pulses that ultimately occur at the output of the DFB are not shown in FIG. 2, but are well known in the art of chirp management lasers and generally follow a frequency deviation.

In another embodiment of the invention, the FM source has control independent of amplitude excursions and frequency excursions. For example, DFB lasers can be used to generate frequency modulation and field absorption (EA) modulators that follow the output of the laser can be used for amplitude modulation and pulse carving. DFB and EA can be integrated on the same chip as shown in FIG.

Separate control of frequency FM and amplitude AM can be used to generate the following DPSK signal. For example, the amplitude modulation generated by the EA modulator is programmed to provide some amplitude modulation following OSR. For example, amplitude modulation can be reduced for bits with large frequency excursions and increased for bits with small frequency modulations, such that the high and low level output amplitudes become equal after OSR. The output amplitude after OSR follows the equation:

(3)

AM (t) + FM (t) x (OSR slope) = constant

Here, AM is amplitude modulation depth in dB defined as the ratio of 1 level to 0 level, FM is frequency modulation in GHz, and slope is OSR slope in dB / GHz. In the above example, where the FM source has separate control over the output amplitude, the AM component can be programmed to the output voltage V _AM when the frequency is half of the maximum, Δf / 2, and the amplitude is frequency When the deviation is maximum, that is, Δf, the amplitude is set to V _AM / 2. Where V _AM is chosen to provide the appropriate amplitude response and depends on the AM slope efficiency of the source.

In another example, the RZ-DPSK uses a DFB / EA as the FM source and OSR at a bit rate, e.g., a 20 GHz bit rate frequency versus a 10 GHz bit rate frequency, ie a 20 GHz bit rate frequency for a 10 Gb / s signal. Reduce the maximum chirp required from the bit rate frequency. This is accomplished by causing a certain phase shift within 100 ps for the full bit period, i.e., 10 Gb / s signal. The EA modulator generates the desired RZ pulse shape with a 50% duty cycle by modulating the output amplitude of the DFB. For example, if a _n = 1 and zero phase is desired, a complete frequency deviation Δf = 10 GHz is applied for 10 Gb / s, so that the phase of the frequency modulated signal is slipped by 10 GHz × 2π × 100ps = 2π. If the input bit is a _n = 0, a three-level digital transformer generates 5 GHz frequency excursions and generates 1/2 voltage. In this case, the phase of the signal slips by 5 GHz × 2π × 100ps = π, so that the last generated adjacent pulses have a π phase shift between them as necessary. The output of the FM source passes through an optical spectrum reshaper (OSR) that raises the amplitude deviation and flattens the chirp, as described in the patent application described above for chirp management lasers (CML).

4 shows an example of an optical spectrum reshaper (OSR) and spectral positions of various frequency values at the output of an FM source. The peak frequency f ₀ corresponding to the highest amplitude is aligned with a relatively low loss point for OSR, while the intermediate frequency f ₁ is aligned with a larger loss (˜10 dB). The frequency f ₂ suffers a larger loss because the frequency is lower (as shown in FIG. 4). Ideally zero energy at the f ₁ and f ₂ levels, eg << 10 dB at peaks of 1 s, is ignored due to the signal level at the output of the OSR. In this example, OSR is used at the transmit tip and is also bandwidth constrained. Various OSR types may introduce identification between the various frequency components to produce a predetermined amplitude response after OSR.

Importantly, the core function of the OSR fleet is U.S. Patent Application No. 11 / 068,032, filed February 28, 2005, by Daniel McGeraffe, et al., Titled OPTICAL SYSTEM COMPRISING AN FM SOURCE AND A SPECTRAL RESHAPING ELEMENT. U.S. Patent Application No. 11 / 084,630 filed March 18, 2005, filed by Daniel McGerefte et al. Under the titles TAYE-31) and (ii) FLAT-TOPPED CHIRP INDUCED BY OPTICAL FILTER EDGE (representative Document No. TAYE-34). As described below, the conversion of the adiabatic chirp at zero to the output of the FM source into a flat peak chirp with a sharp phase shift, the patent application is incorporated herein by reference. The final uniform phase generated by the OSR's transfer function is important for generating an RZ-DPSK signal with improved sensitivity.

Generation of RZ-DPSK

Note that the same concept can be generalized to create a zero return four-phase differential phase shift scheme (RZ-DPSK). For this scheme the information is encoded in four possible phases {0, π / 2, π, -π / 2}. In this case, the corresponding complex region amplitude is {1, i, -1, -i}. In this case, the multilevel digital transformer produces a four level signal V _k as shown below:

(4)

2πΔf _k × T = {2π, π / 2, π, 3π / 2}

Thus, the predetermined frequency deviation becomes Δf _k = {1 / T, 1 / 4T, 1 / 2T, 3 / 4T} for the corresponding phase of {0, π / 2, π, -π / 2}. For example, to generate RZ-DQPSK for a 10 Gb / s RZ signal with a 50% duty cycle, the amplitude of the DMT is applied to a bit that requires 20 GHz, π / 2 phase shift for bits that require zero phase shift. It is adjusted to generate a frequency deviation of 5 GHz for a bit requiring a phase shift and 10 GHz for a bit requiring a phase shift of 3 π / 2. Due to the OSR transmission, during the zero part of the bit, the low level is chosen such that <-10dB below the high level. If the source has separate FM and AM modulation, the amplitude is adjusted to provide a constant amplitude for the output pulses. As is apparent from the above two examples, various multilevel phase coded signals can be generated using the chirp management scheme described above by adjusting the frequency deviation to generate a predetermined phase in a given bit.

transform

It will be appreciated that many changes in the arrangement of details, materials, steps, and components described and illustrated herein to illustrate the nature of the invention may be made by those skilled in the art without departing from the principles and spirit of the invention. .

Included in the details of the present invention.

Claims (38)

A driver having an N level digital multilevel transformer (DMT) configured to receive a two level digital electrical signal representing ones and zeros and to output an N (where N > 2) level electrical signal; An FM source configured to receive the N level electrical signal output by the driver and generate an optical frequency modulated signal; Zero Return Differential Phase Shifter (RZ-DPSK) comprising an Optical Spectrum Reshaper (OSR) configured to receive the optical frequency modulated signal output by the FM source and generate a predetermined RZ-DPSK optical signal ) Optical signal generation system. The method of claim 1, The frequency deviation Δf generated by the FM source is (i) substantially twice the bit rate frequency for one bit input of the two level digital electrical signal, and (ii) is applied to the zero bit input of the two level digital electrical signal. A zero return differential phase shift keying (RZ-DPSK) optical signal generation system in which the output of the driver is adjusted to be equal to a bit rate frequency. The method of claim 1, The output amplitude of the driver is selected to produce a predetermined phase encoding of the DPSK by causing a predetermined frequency deviation and amplitude deviation, so that when (i) zero phase (amplitude = +1) is desired, the driver amplitude is equal to that of the FM source. The output is adjusted to generate a chirp of Δf = 1 / T, and (ii) if π phase (amplitude = -1) is desired, the driver amplitude is adjusted to produce a chirp of Δf = 1 / 2T at the output of the FM source. , Where T is a half time of a bit, zero return differential phase shift (RZ-DPSK) optical signal generation system. The method of claim 3, wherein If zero phase is desired for a 50% duty cycle RZ signal at 10 Gb / s, the driver amplitude is adjusted to produce a Δf = 1 / T chirp at the output of the FM source, where T = 50ps and Δf = 20GHz Signal generation system with zero return differential phase shift keying (RZ-DPSK). The method of claim 3, wherein If π phase is desired for a 50% duty cycle RZ signal at 10 Gb / s, the driver amplitude is adjusted to produce a Δf = 1 / 2T chirp at the output of the FM source, where T = 50ps and Δf = 10GHz Signal generation system with zero return differential phase shift keying (RZ-DPSK). The method of claim 1, Zero return differential phase shift mode (RZ-DPSK) optical signal generation system with N = 3. The method of claim 6, The output amplitude of the driver is selected to produce a predetermined phase coding of QPSK by generating a predetermined frequency deviation and amplitude deviation, so that when (i) zero phase (complex amplitude = + 1) is desired, the driver amplitude is the FM source. Is adjusted to generate a Δf = 1 / T chirp at the output of (ii) if π / 2 phase (complex amplitude = i) is desired, the driver amplitude generates a Δf = 1 / 4T chirp at the output of the FM source. Driver amplitude is adjusted to produce a chirp of Δf = 1 / 2T at the output of the FM source, and (iii) 3π / 2 phase (complex number) when (ⅲ) π phase (complex amplitude = -1) is desired. If amplitude = -i) is desired, the driver amplitude is adjusted to produce a chirp of Δf = 3 / 4T at the output of the FM source, where T is the zero return differential phase shift (RZ-DPSK), which is half the time of the bit. ) Optical signal generation system. The method of claim 7, wherein If π / 2 phase is desired for a 50% duty cycle RZ signal at 10 Gb / s, the driver amplitude is adjusted to produce a chirp of Δf = 1 / 4T at the output of the FM source, where T = 50ps and Δf = Optical signal generation system of zero return differential phase shift method (RZ-DPSK) at 5GHz. The method of claim 7, wherein If 3π / 2 phase is desired for a 50% duty cycle RZ signal at 10 Gb / s, the driver amplitude is adjusted to produce a chirp of Δf = 3 / 4T at the output of the FM source, where T = 50ps and Δf = Optical signal generation system of zero return differential phase shift method (RZ-DPSK) at 15GHz. The method of claim 1, Zero return differential phase shift method (RZ-DPSK) optical signal generation system with N = 4. The method of claim 1, The FM source is a zero return differential phase shift mode (RZ-DPSK) optical signal generation system having a laser. The method of claim 11, The laser is a zero-feedback differential phase shift method (RZ-DPSK) optical signal generation system is a distributed feedback (DFB) laser. The method of claim 1, The FM source provides both amplitude excursions and frequency excursions, and the FM source is configured to provide separate control for the amplitude excursions and the frequency excursions, and zero return differential phase shift keying (RZ-DPSK) optical signal. Generation system. The method of claim 13, The FM source has a field absorption (EA) modulator following a distributed feedback (DFB) laser, the DFB laser is used to generate frequency modulation, and the EA is used for amplitude modulation and pulse carving. Zero Return Differential Phase Shift Mode (RZ-DPSK) optical signal generation system. The method of claim 14, And a zero return differential phase shift keying (RZ-DPSK) optical signal generation system in which the DFB laser and the EA modulator can be integrated on the same chip. The method of claim 1, The OSR comprises a zero return differential phase shift method (RZ-DPSK) optical signal generating system having a filter. The method of claim 16, The FM source provides both amplitude and frequency excursions, and the filter (i) increases amplitude modulation of the signal output by the FM source and (ii) the adiabatic frequency excursion of the FM source. RZ-DPSK optical signal generation system which converts into a flat peak chirp with an instantaneous rapid phase shift near the null output of the signal. (1) receiving a two-level digital electrical signal representing one and zero and outputting an N (where N > 2) electrical signal; (2) receiving the output N-level electrical signal and generating an optical frequency modulated signal; (3) A method for generating an optical signal of zero return differential phase shift (RZ-DPSK), comprising receiving the optical frequency modulated signal and generating a predetermined RZ-DPSK optical signal. The method of claim 18, Step (1) is performed by a driver having an N level digital multilevel transformer (DMT) configured to receive a 2 level digital electrical signal representing 1 and 0 and output an N (where N > 2) level electrical signal. Optical signal generation method of zero return differential phase shift keying (RZ-DPSK). The method of claim 19, In step (2), a zero return differential phase shift keying (RZ-DPSK) optical signal generating method is performed by an FM source configured to receive the N level electrical signal output by the driver and generate an optical frequency modulated signal. . The method of claim 20, Step (3) is a zero return differential phase shift scheme performed by an optical spectrum reshaper (OSR) configured to receive the optical frequency modulated signal output by the FM source and generate a predetermined RZ-DPSK optical signal. RZ-DPSK) optical signal generation method. The method of claim 18, Step (1) is performed by a driver having an N level digital multilevel transformer (DMT) configured to receive a 2 level digital electrical signal representing 1 and 0 and output an N (where N > 2) level electrical signal. Become, Step (2) is performed by an FM source configured to receive the N-level electrical signal output by the driver and generate an optical frequency modulated signal, Step (3) is a zero return differential phase shift scheme performed by an optical spectrum reshaper (OSR) configured to receive the optical frequency modulated signal output by the FM source and generate a predetermined RZ-DPSK optical signal. RZ-DPSK) optical signal generation method. The method of claim 22, The frequency deviation Δf generated by the FM source is (i) substantially twice the bit rate frequency for one bit input of the two level digital electrical signal, and (ii) is applied to the zero bit input of the two level digital electrical signal. A zero return differential phase shift keying (RZ-DPSK) optical signal generation method in which the output of the driver is adjusted to be equal to a bit rate frequency. The method of claim 22, The output amplitude of the driver is selected to produce a predetermined phase encoding of the DPSK by causing a predetermined frequency deviation and amplitude deviation, so that when (i) zero phase (amplitude = +1) is desired, the driver amplitude is equal to that of the FM source. The output is adjusted to generate a chirp of Δf = 1 / T, and (ii) if π phase (amplitude = -1) is desired, the driver amplitude is adjusted to produce a chirp of Δf = 1 / 2T at the output of the FM source. Where optical signal generation method of zero return differential phase shift (RZ-DPSK), where T is 1/2 time of a bit. The method of claim 24, If zero phase is desired for a 50% duty cycle RZ signal at 10 Gb / s, the driver amplitude is adjusted to produce a Δf = 1 / T chirp at the output of the FM source, where T = 50ps and Δf = 20GHz Optical signal generation method of zero return differential phase shift keying (RZ-DPSK). The method of claim 24, If π phase is desired for a 50% duty cycle RZ signal at 10 Gb / s, the driver amplitude is adjusted to produce a Δf = 1 / 2T chirp at the output of the FM source, where T = 50ps and Δf = 10GHz Optical signal generation method of zero return differential phase shift keying (RZ-DPSK). The method of claim 22, Optical signal generation method of zero return differential phase shift method (RZ-DPSK) with N = 3. 28. The method of claim 27, The output amplitude of the driver is selected to produce a predetermined phase coding of QPSK by generating a predetermined frequency deviation and amplitude deviation, so that when (i) zero phase (complex amplitude = + 1) is desired, the driver amplitude is the FM source. Is adjusted to generate a Δf = 1 / T chirp at the output of (ii) if π / 2 phase (complex amplitude = i) is desired, the driver amplitude generates a Δf = 1 / 4T chirp at the output of the FM source. Driver amplitude is adjusted to produce a chirp of Δf = 1 / 2T at the output of the FM source, and (iii) 3π / 2 phase (complex number) when (ⅲ) π phase (complex amplitude = -1) is desired. If amplitude = -i) is desired, the driver amplitude is adjusted to produce a chirp of Δf = 3 / 4T at the output of the FM source, where T is the zero return differential phase shift (RZ-DPSK), which is half the time of the bit. ) Optical signal generation method. 29. The method of claim 28, If π / 2 phase is desired for a 50% duty cycle RZ signal at 10 Gb / s, the driver amplitude is adjusted to produce a chirp of Δf = 1 / 4T at the output of the FM source, where T = 50ps and Δf Optical signal generation method of zero return differential phase shift method (RZ-DPSK) with = 5GHz. 29. The method of claim 28, If 3π / 2 phase is desired for a 50% duty cycle RZ signal at 10 Gb / s, the driver amplitude is adjusted to produce a chirp of Δf = 3 / 4T at the output of the FM source, where T = 50ps and Δf A zero-signal differential phase shift keying (RZ-DPSK) optical signal generation method with = 15 GHz. The method of claim 22, Optical signal generation method of zero return differential phase shift method (RZ-DPSK) with N = 4. The method of claim 22, The FM source is a zero return differential phase shift (RZ-DPSK) optical signal generation method having a laser. 33. The method of claim 32, The laser is a zero-feedback differential phase shift method (RZ-DPSK) optical signal generation method is a distributed feedback (DFB) laser. The method of claim 22, The FM source provides both amplitude excursion and frequency excursion, and the FM source is a zero return differential phase shift scheme (RZ-DPSK) optical signal generation configured to provide separate control for the amplitude excursion and frequency excursion. Way. The method of claim 34, wherein The FM source has a field absorption (EA) modulator following a distributed feedback (DFB) laser, the DFB laser is used to generate frequency modulation, and the EA is used for amplitude modulation and pulse carving. Optical signal generation method of zero return differential phase shift keying (RZ-DPSK). 36. The method of claim 35, And a zero return differential phase shift keying (RZ-DPSK) optical signal generation method in which the DFB laser and the EA modulator are integrated on the same chip. The method of claim 22, And the OSR comprises a zero return differential phase shift method (RZ-DPSK). 39. The method of claim 37, The FM source provides both amplitude and frequency excursions, the filter (i) increases the amplitude modulation of the signal output by the FM source and (ii) the adiabatic frequency excursion of the FM source is null of the signal. RZ-DPSK optical signal generation method that converts into a flat peak chirp with an instantaneous rapid phase shift in the vicinity of the output.

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