JP2009542041A - Versatile compact transmitter generating advanced modulation formats - Google Patents

Abstract

A system for generating a zero-return differential phase shift modulation (RZ-DPSK) optical signal that receives a two-level digital electrical signal representing 1 and 0 and outputs an N (N> 2) level electrical signal A driver comprising an N-level digital multi-level transformer (DMT) configured to: an FM source configured to receive an N-level electrical signal output by the driver and generate an optical frequency modulation signal; A system comprising: an optical spectrum reshaper (OSR) configured to receive an optical frequency modulated signal output by an FM source and generate a desired RZ-DPSK optical signal. A method of generating a zero-return differential phase shift modulation (RZ-DPSK) optical signal comprising: (1) receiving a two-level digital electrical signal representing 1 and 0 and receiving an N (N> 2) level electrical signal (2) receiving an N level electrical signal output and generating an optical frequency modulation signal; and (3) receiving an optical frequency modulation signal and generating a desired RZ-DPSK optical signal. Including methods.

Description

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

(Reference to pending prior patent application)
This patent application
(I) Pending US Patent Application No. 11/272, filed November 8, 2005 by Daniel Magereteh et al. Entitled "POWER SOURCE FOR A DISPENSION COMPENSATION FIBER OPTIC SYSTEM" No. 100 (attorney document number TAYE-59474-00006CON) part continuation application,
(Ii) Daniel Magereteh et al. Entitled "HIGH-SPEED TRANSMISSION SYSTEM COMPRISING A COUPLED MULTI-CAVITY OPTICAL DISCRIMINATOR", filed on Dec. 3, 2002, filed on Dec. 3, 2002. 10 / 308,522 (Attorney document number: TAYE-59474-00007)
(Iii) Pending US patent application Ser. No. 11 / 441,944 filed May 26, 2006 by Daniel Mahgerefte et al. Entitled “FLAT DISFERSION FREQUENCY DISCRIMINATOR (FDFD)”. (Attorney document number TAYE-59474-00009CON) part continuation application,
(Iv) A pending US patent application filed on February 28, 2005 by Daniel Magereteh et al. Entitled "OPTICAL SYSTEM COMPRISING AN FM SOURCE AND A SPECTRAL RESHAPING ELEMENT" 068,032 (Attorney document number: TAYE-31)
(V) pending earlier US patent application Ser. No. 11/084, filed Mar. 18, 2005, by Daniel Magereteh et al. Entitled “FLAT-TOPPED CHIRP INDUCED BY OPTIMAL FILTER EDGE”. This is a continuation-in-part of 630 (Attorney document number TAYE-34)
(Vi) Kevin McCallion, filed in the United States on the 5th of the month, filed by Kevin McCallion, filed in the United States on the 5th patent filed in the United States patent dated 5th month entitled “MULTI-RING RESONATOR IMPLEMENTATION OF OPTICAL SPECTRUM RESHAPER FOR CHIRP MANAGED LASER TECHNOLOGY” 11 / 702,436 (Attorney document number TAYE-23 RR CON) part continuation application,
(Vii) United States patent filed on March 18, 2005 by Daniel Mageleteh et al. Entitled "METHOD AND APPARATUS FOR TRANSMITTING A SIGNAL USING SIMULANTEUS FM AND AM MODULATION" on March 18, 2005 11 / 084,633 (Attorney document number TAYE-33)
(Viii) Pending US Provisional Patent No. 60, filed October 24, 2006 by Kevin McCallion et al. Entitled "SPECTRAL RESPONSE MODIFICATION VIA SPATIAL FILTERING WITH OPTIMAL FIBER" , 867 (Attorney document number TAYE-47B PROV)
(Ix) A pending US patent filed on April 6, 2006 by Daniel Magereteh et al. Entitled "VERSATILE COMPACT TRANSMITTER FOR GENERATION OF ADVANCED MODULATION FORMATS", filed April 6, 2006 , 863 (attorney document number TAYE-73 PROV).

Nine previously identified patent applications are incorporated herein.
The quality and performance of a digital fiber optic transmitter is determined by the distance that the transmitted digital signal can propagate without significant distortion. The bit error rate (BER) of the signal is measured at the receiver after propagating through the dispersion fiber, and the optical power required to obtain a constant BER, i.e. typically ^10-12. (Sometimes called sensitivity) is determined. The difference between the sensitivity at the transmitter output and the post-propagation sensitivity is sometimes referred to as the dispersion penalty. This is usually characterized by the distance at which the dispersion penalty reaches a level of about 1 dB. A standard 10 Gb / s optical digital transmitter, such as an external modulation source, is about 50 km on a standard single mode fiber at 1550 nm before the dispersion penalty reaches a level of about 1 dB, sometimes referred to as the dispersion limit. Can be transmitted up to a distance. The dispersion limit is that the digital signal is conversion limited, i.e. the signal does not have a time-varying phase over its bits for a standard 10 Gb / s transmission, a 100 ps bit period or 1 / (bit rate ). Another measure of transmitter quality is the absolute sensitivity after fiber propagation.

  In prior art fiber optic systems, there are three types of optical transmitters: (i) direct modulation laser (DML), (ii) electroabsorption modulated laser (EML), and (iii) external modulation Mach-Zehnder ( MZ) modulators are currently used. For transmission in standard single mode fiber at 10 Gb / s and 1550 nm, the MZ modulator and EML may have the longest reach, and is generally considered to reach 80 km. Using a special coding scheme called phase-shaping duobinary, an MZ transmitter can reach 200 km. On the other hand, direct modulation lasers (DML) usually reach less than 5 km. This is because the inherent time-dependent chirp of the DML causes a large distortion of the signal after that distance.

  For example, at 10 Gb / s on a single mode fiber, it increases the reach of DML to more than 80 km, and for various long-range optical data transmissions (more than 80 km at 10 Gb / s) through an optical fiber. This system is incorporated by reference into the present application and is filed on November 8, 2005 by Daniel Magereteh et al., Entitled “i) POWER SOURCE FOR A DISPENSION COMPENSATION FIBER OPTIC SYSTEM”. US Patent Application No. 11 / 272,100 (attorney document number TAYE-59474-00006CON), (ii) “FLAT DISFERSION FREQUENCY DISCRIMINATOR (F FD) ", US patent application Ser. No. 11 / 441,944 filed May 26, 2006 (Attorney document no. TAYE-59474-00009CON), filed May 26, 2006, And US Patent Application No. 308, filed on March 12, 2002, by Daniel Magereteh et al. Entitled "HIGH-SPEED TRANSMISSION SYSTEM COMPRISING A COUPLED MULTI-CAVITY OPTICAL DISCRIMINATOR", US Patent No. 308, filed on Dec. 30, 2003. No. 522 (attorney document number TAYE-59474-00007). The transmitter associated with these new systems may be referred to as Chirp Managed Laser (CML ™) by Azna LLC in Wilmington, Massachusetts. . In these new systems, the frequency modulation (FM) source involves an optical spectrum reshaper (OSR), which uses frequency modulation to increase the amplitude modulated signal, and Partially compensate for dispersion in the transmit fiber. In one embodiment, the frequency modulation source may comprise a direct modulation laser (DML). An optical spectrum reshaper (OSR), sometimes referred to as a frequency discriminator, can be formed by a suitable optical element, such as a filter, having wavelength dependent transmission capabilities. The OSR can be adapted to convert frequency modulation to amplitude modulation.

  In the novel system of the present invention, the chirp characteristic of a frequency modulation source is utilized, which is then CML ™ transmitter over a standard single mode fiber with an OSR of 10 Gb / s and 1550 nm. Is further reshaped by configuring it so as to further extend the reach distance to 250 km or more. The novel system of the present invention is, among others, Daniel Mageret et al. (I) entitled “OPTICAL SYSTEM COMPRISING AN FM SOURCE AND A SPECTRAL RESHAPING ELEMENT”, whose patent application is incorporated herein. Entitled US Patent Application No. 11 / 068,032 (Attorney's Document No. TAYE-31), filed February 28, 2005, (ii) “FLAT-TOPPPED CHIRP INDUCED BY OPTICAL FILTER EDGE” US patent application Ser. No. 11 / 084,630 filed Mar. 18, 2005 by Daniel Mageleref et al. No. TAYE-34), (iii) Kevin Macalion et al., Entitled “MULTI-RING RESONATOR IMPLEMENTATION OF OPTICAL SPECTRUM RESHAPER FOR CHIRP MANAGED LASER TECHNOLOGY” US Patent Application No. 11 / 702,436 (attorney document number TAYE-23 RR CON) and (iv) "METHOD AND APPARATUS FOR TRANSMITTING A SIGNAL USING SIMULTANEOUS FM AND AM MODULATION ELLE"・ Magelete (Daniel Mahgere teh) Other by combining selected features of the system described in application U.S. Patent Application Serial No. 11 / 084,633 (Attorney Docket No. Taye-33) on March 18, 2005.

  More particularly, the present invention generates an optical differential phase shift modulation (DPSK) return-to-zero (RZ) signal using a chirp managed laser of the type described in the previously identified patent application. Provide a device.

In another aspect of the invention, a system is provided for generating a zero return zero return differential phase shift modulation (RZ-DPSK) optical signal, the system comprising:
A driver comprising an N-level digital multi-level transformer (DMT) configured to receive a 2-level digital electrical signal representing 1 and 0 and to output an N (N> 2) level electrical signal;
An FM source configured to receive an N-level electrical signal output by the driver and generate an optical frequency modulated signal;
An optical spectrum reshaper (OSR) configured to receive an optical frequency modulated signal output by an FM source and generate a desired RZ-DPSK optical signal.

In another aspect of the invention, a method for generating a zero return differential phase shift modulation (RZ-DPSK) optical signal is provided, the method comprising:
(1) receiving a two-level digital electrical signal representing 1 and 0 and outputting an N (N> 2) level electrical signal;
(2) receiving an N level electrical signal output and generating an optical frequency modulated signal; and
(3) receiving an optical frequency modulated signal and generating a desired RZ-DPSK optical signal.

These and other objects, features and advantages of the present invention will be more fully disclosed or will become apparent from the following detailed description of preferred embodiments of the invention considered in conjunction with the accompanying drawings. I will. In the accompanying drawings, like numerals refer to like parts. DPSK Format In the DPSK format, an input digital electrical signal representing 1 and 0 is converted into an optical signal in which information is encoded into the phase of a continuous wave (CW) constant amplitude signal. In this DPSK format, given the input random digital sequence of 1 and 0 bits, the modulation rule changes the phase of the CW signal by π for all occurrences of 0 bits, while 1 bit The phase is invariant with respect to the occurrence of. As an example, consider the digital sequence of bits shown in Table 1 below and the resulting DPSK phase.

Here, the amplitude refers to the optical electric field of the bit carrying phase information, while the intensity refers to the optical output of the bit that does not carry phase information. The optical field representation of each bit is a complex number, while the light intensity is always a real positive number. The advantage of this modulation format is that it provides the same bit error rate as standard on-off modulation at a signal-to-noise ratio as small as 3 dB, thereby increasing the number of optical amplifiers resulting in long transmission distances. It is possible to transmit across. This is because in the DPSK format, all bits carry energy, and in a non-zero return on-off modulation (OOK) scheme, only 1 bit has energy and 0 bits do not carry energy. .

  The benefits of DPSK are realized by using a 1-bit delay interferometer at the receiver with a balanced receiver. The function of the 1-bit delay interferometer is to convert DPSK phase modulation into amplitude modulation. The interferometer has two outputs: an ADD output where a 1-bit delayed version of (1) bits is added and a SUBTACT output where a 1-bit delayed version of (2) bits is subtracted from each other. Since the input DPSK signal is split between the two arms of the interferometer, the output of each arm is reduced by a factor of two. The function of an interferometer that is typically a Mach-Zehnder type is shown in the example in Table 2 below. Here, the amplitude sequence (c) is delayed by one bit in one arm of the Mach-Zehnder interferometer to produce a stream (d) that is caused to interfere with the input of the Mach-Zehnder, thereby An ADD output (e) and a SUBTRACT output (f) are generated. The intensity of these two outputs is detected by a standard photodetector that is insensitive to the phase of the optical field and only measures the light output. It is known in the art that a 2-port balanced receiver subtracts the photocurrent detected at the ADD port from the photocurrent detected at the SUBTRACT port and is 3 dB more sensitive than a standard OOK transmitter. Output (g).

The bit uses a digitizer that assigns a bit value of 1 if the output V of the receiver exceeds a certain voltage value (sometimes called a decision threshold) and a value of 0 if the output voltage V is less than the decision threshold. By the receiver. As is known in the art, the decision threshold for the DPSK modulation format is set at 0 volts, so the so-called “distance” between the 1 and 0 bits is here 2 is there. That is, the voltage difference between the 1 bit and the 0 bit is 1 − (− 1) = 2, while assuming that the average optical power is the same, for standard OOK, the difference is 1− 0 = 1. This double difference allows the same bit error rate to be obtained at half of the standard OOK optical signal-to-noise ratio (OSNR), and thus DPSK is 3 dB advantageous.

  In a zero-return differential phase shift modulation (RZ-DPSK) transmitter, the output of the CW laser is a sinusoidal clock signal of a selected bit rate (eg, 10 GHz) with a 30% to 50% duty cycle. Further modulation will further improve the sensitivity at the receiver. Thus, the output intensity is a constant intensity pulse train with a 30% to 50% duty cycle at that bit rate, while the phase of the pulses follows the DPSK rules described above.

In the prior art, an RZ-DPSK transmitter is typically a CW laser, a first modulator that generates DPSK, and a second modulation that carves out 30% to 50% duty cycle pulses or higher sensitivity. Equipped with a bowl. The modulators used in the prior art are typically Mach-Zehnder phase and / or amplitude modulators, which are bulky and require a high (ie, greater than 4-6V _pp ) drive voltage, and therefore have high power consumption. Is not desirable.

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

  FIG. 1 shows a schematic diagram of the novel apparatus. The binary electrical digital data stream is fed into a digital multi-level transformer (DMT), which converts the binary electrical digital data stream into a three level output according to the procedure described below. The tri-level digital signal coming out of the DMT is then used to drive the FM source, and the FM source (eg, a distributed feedback laser, also known as a DFB laser) receives the input digital tri-level signal as an optical tri-level signal. Convert to In other words, the output of the DMT is used as an input to the CML device. Both the optical frequency and light intensity of the laser output will be modulated according to the three level driver signal output by the DMT.

  The amplitude of the electrical signal output by the DMT is selected to generate a defined frequency shift and amplitude shift, thereby generating the desired phase coding of DPSK, i.e. (i) zero phase, That is, when amplitude = + 1 is desired, the driver amplitude is adjusted to produce a chirp Δf = 2 / T at the laser output, where T is 1/2 the bit duration, eg, 10 Gb When the 50% duty cycle RZ signal of / s is 50 ps and (ii) π phase, ie amplitude = −1, is desired at the coded DPSK output, the driver amplitude is chirp Δf = 1 / at the laser output. T is generated. The phase shift over zero bits is Δφ = 2πTΔf, so for a 10 Gb / s 50% duty cycle RZ-DPSK signal, 0 phase shift (amplitude = + 1), chirp = 20 GHz, and π phase shift Note that for (amplitude = -1), chirp = 10 GHz.

  The optical output of the FM source then passes through an optical spectrum reshaper (OSR), i.e. a filter, which has two functions. That is, (i) the OSR increases the amplitude modulation of the output signal, and (ii) the OSR causes the input adiabatic frequency shift (output by the FM source) to be a nearly instantaneous abrupt near the null output of the signal. Convert to flat top chirp with phase shift.

  To further elucidate this novel approach, input binary digital bit sequences as input to a three-level digital transformer (DMT)

think of. FIG. 2 shows the bit sequence and pulse waveforms at various points in the transmitter chain (ie, transmitter stage). The desired output sequence b _n , labeled “desired output” in FIG. 2, is another binary digital sequence having two values, here considered to be +1 and −1. . The sequence _{b n,} bits of the value of _{b n} are, for all occurrences of bit 0 of _{a n,} varies from its previous value _{b n-1,} whereas, for the occurrence of one bit of _{a n,} invariant according to the rule that remains can be related to the input sequence a _n. In conventional RZ-DPSK transmitters, this sequence is generated by the use of a differential encoder in combination with a Mach-Zehnder modulator. In the present invention, a differential encoder is no longer needed. If b _n = + 1 or −1, this rule is

Can be rewritten as: The sequence a _n, is supplied to the three level digital transformer (DMT), DMT, in the pulse waveform (the example shown in FIG. 2 at the point B according to the following rules, the desired output pulse, a 50% duty cycle To have). The rules are as follows: (I) When the input bit is a _n = 1, the signal at point B drops to 0 (changes by V), stays at 0 value for 50% of the bit duration 2T, and reaches the value V The return-voltage drop V is adjusted according to the FM efficiency of the laser to produce a chirp equal to twice the bit rate frequency (Δf = 1 / T). (Ii) When the input bit is a = 0, the output drops to V / 2, stays at that value for period T, returns to value V, and the bit rate frequency, ie Δf = 1 Generate a chirp equal to / 2T.

This selection of voltage output ensures the generation of an appropriate phase relationship between the bits of the frequency modulation (FM) source output described below. An FM source, such as a DFB laser, is driven by a voltage pattern at point B and generates a frequency and amplitude modulated output waveform as shown at point C (frequency and phase profiles are shown, but no amplitude profile is shown). The value V of the drive voltage is selected to produce a frequency shift equal to 10 GHz for a digital signal bit rate, ie, a 10 Gb / s data stream having a 50% duty cycle. More generally, the total frequency deviation Δf is selected to be Δf × T = 1, where T is the zero duration of the zero return signal, ie 50% duty cycle RZ pulse · One half of the bit period for the sequence. The voltage is determined by the so-called FM efficiency η _FM (GHz / V unit) of the signal source, in other words, Δf = η _FM V. The phase of the optical signal at the output of the DFB laser is the time integration of the frequency shift shown in FIG. For example, when a _n = 1 and 0 phase is desired, the total frequency deviation Δf = 20 GHz is applied to a 10 Gb / s zero return (RZ) data stream with a 50% duty cycle, so the frequency The phase of the modulation signal is shifted by 20 GHz × 2π × 50 ps = 2π. When the input bit is a _n = 1, the three-level digital transformer (DMT) generates 1/2 of the voltage and generates a 10 GHz frequency shift for 10 Gb / s RZ. In this case, the phase of the signal is shifted by 10 GHz × 2π × 50 ps = π, and the resulting adjacent pulse will have a π phase shift between the pulses as desired.

  The output of the FM source (eg, laser) is passed through an optical spectrum reshaper (OSR), i.e., a filter, which has an amplitude as described in the above-mentioned patent application related to chirp managed lasers. Increase the deviation and flatten the chirp. As shown in FIG. 2, the intensity at the output of the OSR is an RZ-DPSK signal where each bit carries the same energy and the data is encoded in the phase of the bits.

The amplitude of the pulse obtained at the output of the DFB is not shown in FIG. 2, but usually follows a frequency shift, as is well known in the art of chirp managed lasers.
In another embodiment of the present invention, the FM source can be independently controlled for amplitude and frequency shift. For example, a DFB laser can be used to generate frequency modulation, and an electroabsorption (EA) modulator that follows the output of the laser can be used for amplitude modulation and pulse carving. The DFB and EA can be integrated on the same chip as shown in FIG.

  Using independent control of frequency (FM) and amplitude (AM), the DPSK signal can be generated as follows. For example, the amplitude modulation generated by the EA modulator is programmed to provide the desired amplitude modulation after OSR. For example, amplitude modulation is reduced when a bit has a large frequency shift and increased when a bit has a small frequency shift, so that the high and low level output amplitudes after OSR are the same. The output amplitude after OSR is

Follow. Where AM is the amplitude modulation depth in dB, defined as the ratio of level 1 to level 0, FM is frequency modulation in GHz, and the slope is the OSR slope in dB / GHz. It is. In the above example, if the FM source controls the output amplitude independently, the AM component will be programmed to output the voltage V _AM when the frequency is half of the maximum value, ie Δf / 2, When the frequency shift is maximum, ie Δf, the amplitude is set to V _AM / 2. Here, V _AM is selected to provide an appropriate amplitude response and depends on the AM slope efficiency of the signal source.

In another example, using a DFB / EA combination as the FM source and OSR, RZ-DPSK occurs at a bit rate, eg, 10 Gb / s, and the maximum required chirp is 10 Gb / s signal Decreases from twice the bit rate frequency, i.e., 20 GHz, to a bit rate frequency, i.e., 10 GHz, for a 10 Gb / s signal. This is accomplished by generating the desired phase shift within a full bit period, ie 100 ps, for a 10 Gb / s signal. The EA modulator generates the desired RZ pulse shape with 50% duty cycle by modulating the amplitude of the output of the DFB. For example, when a _n = 1 and 0 phase is desired, the total frequency shift Δf = 10 GHz is applied to the 10 Gb / s signal, so the phase of the frequency modulated signal is only 10 GHz × 2π × 100 ps = 2π. Shift. When the input bit is a _n = 0, the three-level digital transformer generates half of the voltage and generates a 5 GHz frequency shift. In this case, the phase of the signal is shifted by 5 GHz × 2π × 100 ps = π, and the resulting adjacent pulse will have a π phase shift between the pulses as desired. The optical output of the FM source passes through an optical spectrum reshaper (OSR), i.e. a filter, which is amplitude biased as described in the above-mentioned patent application relating to chirp managed lasers (CML). Increase transfer and flatten chirp.

FIG. 4 shows an example of the spectral position of various frequency values at the output of an optical spectrum reshaper (OSR) and FM source. Here, the peak frequency f ₀ corresponding to the maximum amplitude is aligned with a relatively low loss point on the OSR, while the intermediate frequency f ₁ is aligned with a high loss (about 10 dB). Frequency f ₂ (as shown in FIG. 4) for a lower frequency, subjected to a large loss. Ideally, the signal level at the output of the OSR, 0 energy _{f 1} levels and _{f 2} level in less than the energy of the peak of 1s, negligible, for example, is such that less than -10 dB. In this example, OSR is used at the transmit edge and is bandwidth limited. Different OSR shapes can introduce discrimination between different frequency components to generate the desired amplitude response after OSR.

  Importantly, an important function of the OSR edge is that Daniel Magelet (Daniel) entitled “OPTICAL SYSTEM COMPRISING AN FM SOURCE AND A SPECTRAL ELEMENT”, which is incorporated herein by reference. US Patent Application No. 11 / 068,032 (Attorney Document No. TAYE-31) and (ii) “FLAT-TOPPPED CHIRP INDUCED BY OPTICAL FILTER EDGE” filed February 28, 2005 by Mahgerefte et al. US patent application Ser. No. 11 / 084,630, filed Mar. 18, 2005, by Daniel Magereteh et al. It should be noted that this is a conversion of the adiabatic chirp of the output of the FM source to a flat top chirp with a sudden phase shift at 0, as described in the actuary document number TAYE-34). is there. The resulting uniform phase generated by the OSR transfer function is important when generating an RZ-DPSK signal with improved sensitivity.

RZ-QPSK Generation The same idea is used to generate a Zero Return Quadrature Phase Shift Modulation (RZ-QPSK) in which information is coded in four possible phases {0, π / 2, π, −π / 2}. Note that it can be generalized. The corresponding complex field amplitude is {1, i (OSR) -1, -i}. In this case, the multilevel digital transformer is

A four-level signal V _k is generated. Thus, the desired frequency shift is Δf _k = {1 / T, 1 / 4T, 1 / 2T, 3 / 4T} for the corresponding phase of {0, π / 2, π, −π / 2}. is there. For example, for a 10 Gb / s RZ signal with 50% duty cycle, to generate RZ-QPSK, the DMT amplitude is 20 GHz for bits that require 0 phase shift, bits that require π / 2 phase shift Is adjusted to generate a frequency shift of 5 GHz, 10 GHz for bits that require a π phase shift, and 15 GHz for bits that require a 3π / 2 phase shift. The OSR transmission is selected such that the low level during the 0 portion of the bits is less than -10 dB below the high level. If the signal source has independent FM and AM modulation, the amplitude is adjusted to provide a constant amplitude for the output pulse. As can be seen from the above two examples, the various chirped managed lasers described above by adjusting the frequency shift to produce the desired phase in the desired bits for the various multilevel phase coded signals. It can be generated by using a scheme.

To illustrate the nature of the modifications present invention, as described herein, it has been shown, information on the elements, materials, many changes in steps, and arrangement without departing from the principles and scope of the present invention, It will be appreciated that this may be done by one skilled in the art.

1 is a schematic diagram of a chirp managed laser based RZ-DPSK transmitter of the present invention. FIG. 4 shows a bit sequence progression along a transmitter chain in a chirp managed laser RZ-DPSK source. The figure which shows the DFB laser which has an electroabsorption modulator. FIG. 5 shows the relative spectral positions of various frequency modulation levels within the OSR and FM source tri-level signal output.

Claims (38)

A system for generating a zero return differential phase shift modulation (RZ-DPSK) optical signal comprising:
A driver including an N-level digital multilevel transformer (DMT) configured to receive a 2-level digital electrical signal representing 1 and 0 and to output an N-level electrical signal satisfying N> 2.
An FM source configured to receive the N-level electrical signal output by the driver and generate an optical frequency modulated signal;
A system comprising: an optical spectrum reshaper (OSR) configured to receive the optical frequency modulated signal output by the FM source and generate a desired RZ-DPSK optical signal. The output of the driver is such that the frequency shift (Δf) generated by the FM source is (i) substantially equal to twice the bit rate frequency for the bit of input 1 of the two-level digital electrical signal. The system of claim 1, wherein (ii) the input 0 bit of the two-level digital electrical signal is adjusted to be equal to the bit rate frequency. The amplitude of the driver output is selected to produce a defined frequency shift and amplitude shift, where T is 1/2 of the duration of the bit, thereby (i) zero phase (amplitude = When +1) is desired, the driver amplitude is adjusted to produce a chirp Δf = 1 / T at the output of the FM source, and (ii) when π phase (amplitude = −1) is desired, the driver The system of claim 1, wherein the amplitude is adjusted to produce a desired phase coding of the DPSK such that the amplitude is adjusted to produce a chirp Δf = ½T at the output of the FM source. When zero phase is T = 50 ps, Δf = 20 GHz, and a 50% duty cycle RZ signal is desired at 10 Gb / s, the driver amplitude is a chirp of Δf = 1 / T at the output of the FM source. The system of claim 3, wherein the system is adjusted to generate When the π phase is T = 50 ps, Δf = 10 GHz, and a 50% duty cycle RZ signal is desired at 10 Gb / s, the driver amplitude is a chirp of Δf = 1 / 2T at the output of the FM source. The system of claim 3, wherein the system is adjusted to generate The system of claim 1, wherein N = 3. The amplitude of the output of the driver is selected to produce a defined frequency shift and amplitude shift, where T is half the duration of the bit, thereby (i) zero phase (complex amplitude) = + 1) is desired, the driver amplitude is adjusted to produce a chirp Δf = 1 / T at the output of the FM source, and (ii) π / 2 phase (complex amplitude = i) is desired When the driver amplitude is adjusted to produce a chirp Δf = 1 / 4T at the output of the FM source, and (iii) when π phase (complex amplitude = −1) is desired, the driver amplitude is When adjusted to produce chirp Δf = 1 / 2T at the source output and (iv) 3π / 2 phase (complex amplitude = −i) is desired, the driver amplitude is chirp Δf at the FM source output. = Adjusted to generate 3 / 4T As to produce the desired phase coding of the QPSK, system according to claim 6. When the π / 2 phase is T = 50 ps, Δf = 5 GHz, and a 50% duty cycle RZ signal at 10 Gb / s is desired, the driver amplitude is Δf = 1 / 4T at the output of the FM source. The system of claim 7, wherein the system is adjusted to generate a chirp of When the 3π / 2 phase is T = 50 ps, Δf = 15 GHz, and a 50% duty cycle RZ signal at 10 Gb / s is desired, the driver amplitude is Δf = 3 / 4T at the output of the FM source. The system of claim 7, wherein the system is adjusted to generate a chirp of The system of claim 1, wherein N = 4. The system of claim 1, wherein the FM source includes a laser. The system of claim 11, wherein the laser is a distributed feedback (DFB) laser. The FM source provides both amplitude deviation and frequency deviation, and further, the FM source is configured to provide independent control over the amplitude deviation and the frequency deviation. The described system. The FM source includes a distributed feedback (DFB) laser followed by an electroabsorption (EA) modulator, which is used to generate frequency modulation, the EA modulator comprising amplitude modulation and pulse 14. A system according to claim 13, used for carving. The system of claim 14, wherein the DFB laser and the EA modulator are integrated on the same chip. The system of claim 1, wherein the OSR includes a filter. The FM source provides both an amplitude shift and a frequency shift, and the filter (i) increases the amplitude modulation of the signal output by the FM source, and (ii) the adiabatic frequency of the FM source. The system of claim 16, wherein the shift is converted to a flat top chirp with a near instantaneous abrupt phase shift near the null output of the signal. A method of generating a zero return differential phase shift modulation (RZ-DPSK) optical signal comprising:
(1) receiving a two-level digital electrical signal representing 1 and 0 and outputting an N-level electrical signal satisfying N> 2.
(2) receiving the N-level electrical signal output and generating an optical frequency modulated signal; and
(3) A method comprising receiving the optical frequency modulation signal and generating a desired RZ-DPSK optical signal. Step (1) is a N-level digital multi-level transformer configured to receive a two-level digital electrical signal representing 1 and 0 and to output an N-level electrical signal that satisfies N> 2. 19. The method of claim 18, wherein the method is implemented by a driver that includes (DMT). 19. The method of claim 18, wherein 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 modulation signal. Step (3) is performed by an optical spectrum reshaper (OSR) configured to receive the optical frequency modulated signal output by the FM source and generate the desired RZ-DPSK optical signal. The method of claim 18. Step (1) is an N-level digital multi-level transformer configured to receive a 2-level digital electrical signal representing 1 and 0 and output an N-level electrical signal when N> 2 is satisfied. Implemented by a driver with DMT),
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 performed by an optical spectrum reshaper (OSR) configured to receive the optical frequency modulated signal output by the FM source and generate a desired RZ-DPSK optical signal. Item 19. The method according to Item 18. The output of the driver is such that the frequency shift (Δf) generated by the FM source is (i) substantially equal to twice the bit rate frequency for the bit of input 1 of the two-level digital electrical signal. 23. The method of claim 22, wherein (ii) the input 0 bit of the two-level digital electrical signal is adjusted to be equal to the bit rate frequency. The amplitude of the driver output is selected to produce a defined frequency shift and amplitude shift, so that (i) when zero phase (amplitude = + 1) is desired, the driver amplitude is T Is adjusted to produce a chirp Δf = 1 / T at the output of the FM source when ½ of the duration of the bit, and (ii) when π phase (amplitude = −1) is desired 23. The method of claim 22, wherein a driver amplitude is generated to produce a desired phase coding of the DPSK such that a driver amplitude is adjusted to produce a chirp Δf = 1 / 2T at the output of the FM source. When T = 50 ps, Δf = 20 GHz, and zero phase, a 50% duty cycle RZ signal at 10 Gb / s is desired, the driver amplitude is a chirp of Δf = 1 / T at the output of the FM source. 25. The method of claim 24, wherein the method is adjusted to generate When T = 50 ps, Δf = 10 GHz, and a π phase of 50% duty cycle RZ signal at 10 Gb / s is desired, the driver amplitude is a chirp of Δf = 1 / 2T at the output of the FM source 25. The method of claim 24, wherein the method is adjusted to generate 23. The method of claim 22, wherein N = 3. The amplitude of the driver's output is selected to produce a specified frequency and amplitude shift, so that when T is half the duration of the bit, (i) zero phase (complex When amplitude = + 1) is desired, the driver amplitude is adjusted to produce a chirp Δf = 1 / T at the output of the FM source, and (ii) π / 2 phase (complex amplitude = i) is desired The driver amplitude is adjusted to produce a chirp Δf = 1 / 4T at the output of the FM source, and (iii) when π phase (complex amplitude = −1) is desired, the driver amplitude is When adjusted to produce chirp Δf = 1 / 2T at the output of the FM source and (iv) 3π / 2 phase (complex amplitude = −i) is desired, the driver amplitude is chirped at the output of the FM source. Adjust to generate Δf = 3 / 4T As it will be to produce the desired phase coding of the QPSK, The method of claim 27. When T = 50 ps, Δf = 5 GHz, and π / 2 phase, a 50% duty cycle RZ signal at 10 Gb / s is desired, the driver amplitude is Δf = 1 / 4T at the output of the FM source. 29. The method of claim 28, wherein the method is adjusted to produce a chirp of. When T = 50 ps, Δf = 15 GHz, and 3π / 2 phase, a 50% duty cycle RZ signal at 10 Gb / s is desired, the driver amplitude is Δf = 3 / 4T at the output of the FM source. 29. The method of claim 28, wherein the method is adjusted to produce a chirp of. 23. The method of claim 22, wherein N = 4. 24. The method of claim 22, wherein the FM source includes a laser. 33. The method of claim 32, wherein the laser is a distributed feedback (DFB) laser. 23. The FM source provides both amplitude deviation and frequency deviation, and further, the FM source is configured to provide independent control over the amplitude deviation and the frequency deviation. The method described in 1. The FM source includes a distributed feedback (DFB) laser followed by an electroabsorption (EA) modulator that is used to generate frequency modulation, the EA modulator comprising amplitude modulation and pulse 35. A method according to claim 34 used for carving. 36. The method of claim 35, wherein the DFB laser and the EA modulator are integrated on the same chip. 24. The method of claim 22, wherein the OSR includes a filter. The FM source provides both an amplitude shift and a frequency shift, and the filter (i) increases the amplitude modulation of the signal output by the FM source, and (ii) the adiabatic frequency of the FM source. 38. The method of claim 37, wherein the shift is converted to a flat top chirp with a near instantaneous abrupt phase shift near the null output of the signal.