WO2013053029A1 - Method and device for removing the modulation of an optical carrier and adding a new modulation - Google Patents

Abstract

The present invention patent application relates to a method and to a device for removing the modulation of an amplitude modulated optical carrier wave and adding a new modulation. The invention can be applied in optical networks having centralised light sources for implementing the fiber-to-the-home connection structure, allowing the downstream channel to be remodulated with new information in order to operate as an upstream channel and carry return data without requiring an additional wavelength. Channel re-use doubles the capacity of a system with a fixed number of channels, dispensing with a light source at the final/remote user location.

Description

 METHOD AND DEVICE FOR WITHDRAWING MODULATION FROM AN OPTICAL CARRIER AND INTRODUCTION OF A NEW MODULATION. Field of the invention

 The present patent application relates to an amplitude modulated optical carrier wave erasing method and a remodeling photonic eraser device. Further, the present invention relates to the uses of such a wave erasing and remodeling device.

 The invention can be applied to optical networks with centralized light sources in the implementation of the fiber-to-the-home FTTH structure so that the descent channel can be remodulated with new information, operating as a rising channel, bringing back data without the need for additional wavelength. Channel reuse doubles the capacity of a system with a fixed number of channels, eliminating the need for light source at the end / remote user point.

 Fundamentals of the invention

Optical networks with centralized light sources are one of the solutions for implementing the FTTH structure. FTTH technology can provide increased access network capacity by meeting the demand for integration and evolution of telecommunications services involving voice / image traffic, e-banking, logistics and other advanced interactive media services. However, the finite number of channels available in such systems, mostly built with passive devices, may limit the total system capacity. In this sense, it is interesting to reuse the optical carrier generated at the central unit as a way of supplying power to the end-user return channel. In optical carrier reuse schemes, the original modulation of a downward channel is erased and this channel can then be re-modulated with new information, now operating as an upward channel, taking the return data without the need for wavelength use. additional. Channel reuse initially doubles the capacity of a fixed-channel system and eliminates the need for light source at the end / remote user point.

Wave erasure consists of extinction radius reduction (ER) after UL-SOA operation. The ER is defined by: £ i? = 101og [^ ^{P, op ~ Pdark} ^]

Where Pt _op and P _bas e are the power levels of the high and low signals, respectively, of the modulation amplitude; while Pdark is the dark noise level.

 Saturated optical gain in semiconductor optical amplifiers (SOA) to provide for the erasure of optical data was first proposed in 1993 (S. Ho. E. Conforti, and SM Kang, local area network ", IEEE CLEO (1993), 416-417.) using cascading SOAs. The methods using cascading SOAs do not allow total carrier erasure, ie the optical signal at the end of the process maintains some non-negligible residual modulation level, as well as large overshoots inherent to amplification with conventional devices (cavity < 1 mm).

The process of erasing and remodeling with a reflective SOA (R-SOA) operating at speeds up to 1 Gbps (TY Kim and SK Han, "WDM-PON Reflective SOA-based sharing optical source for up / downlink data and broadcasting transmission ", IEEE Photon. Technol. Lett. 18, 2350-2352 (2006)). This system has been commercially implemented in Korea, with a capacity of up to 512 end users on a single optical fiber. However, the system operates with penalties of up to 16 dB in the remodulation process due to the considerable tweeting present on the carrier which, due to the limitations inherent in this R-SOA system, is only partially erased.

 Other techniques have been proposed such as the use of two modulators (K.C. Reichmann, N.J. Frigo, and P.P. lannone, "Wavelength registration in WDM ring networks by reconstitution of dropped optical carriers", ECOC, 136-137 (1999)); forward feedback semiconductor optical amplifier (SOA) system for dynamic gain control in conjunction with optical modulator (E. Conforti, CM Gallep, S. Ho, AC Bordonalli, and SM Kang, "Carrier reuse with gain compression") and feed-forward semiconductor optical amplifier, "IEEE Trans. Microwave Theory Tech. 50, 77-81 (2002)), single SOA as eraser and re-modulator (H. Takesue and T. Sugie," Wavelength channel data rewrite using saturated SOA modulator for WDM metro / access networks with centralized light sources ", IEEE J. Lightw. Technol. 21, 2546-2556 (2003)), R-SOA (JH Yu, N. Kim, and BW Kim," Remodulation schemes with reflective SOA for colorless DWDM PON "J. Opt. Netw. 6, 1041 -1054 (2007)) and R-SOA (Z. Xu, YJ Wen, WD Zhong, M. Attygall, X. Cheng , Y. Wan, T. Hiang Cheng, and C. Lu, "WDM-PON architectures with a single shared interferometric filter for carrier-upstream transmission," IEEE J. Light W. Technol. 25, 3669-3677 (2007)), mainly.

 US1997 / 5610744 proposes erasing information on the optical carrier using a series (array) of three or more saturating optical amplifiers. However, when switching from one amplifier to another, the signal is attenuated, making it difficult to erase and making the system more expensive due to the use of multiple semiconductor optical amplifiers.

US2007 / 0183788 utilizes R-SOA with current feedback aid for dynamic gain control. However, the system erases amplitude modulated optical carriers at rates limited to a few (less than 2) Gbps, and with satisfactory operation only for modulated signals. with small extinction ratio (ER <4 dB). Such limits make the system unreliable to varying input signal quality, which would necessarily have to have low optical power excursion, and make it impossible to expand to higher modulation speed channels (up to 10 Gbps, currently commercial).

 The methods using cascading SOAs do not allow total carrier erasure, ie the optical signal at the end of the process maintains some non-negligible residual modulation level, besides large chirps (greater than 10% of total excursion) in amplitude inherent to amplification. with conventional devices (cavity <1 mm). This is because in small cavities, even with high input signals, the SOA is not deeply saturated in much of its active region, so level transitions (mainly from "0" to "1") end up with the mentioned chirps. . Only by means of ultra long cavities (greater than 4 mm), as in the proposed invention, can the device be used for erasing efficiently without chirping and modulating debris.

 For blanking to be satisfactory, the UL-SOA device must operate in its saturation region (optical gain decreases with increasing optical power). Since power at level "0" may be significantly lower than power at level "1", the difference between gains from levels "0" and "1" results in a reduction of the desired ER value for the output signal.

 The erasability presented by the mentioned techniques is not substantial in many of the cases demanded in real networks, explicitly when considering signals for the descent channel with pseudo random bit stream (PRBS) and amplitude modulated (AM) sequences. ) with modulation depth, ie ER greater than 8 dB; and / or signals with high bit rates exceeding 2.5 Gbps.

Given the above, it would be useful if the technique had a device and erasing method that could operate in sequences PRBS, θ modulated in amplitude with ER greater than 8dB and with rates higher than 2.5 Gbps, which are cases demanded by real networks.

 The present invention proposes an erasure device that has been shown to be efficient for an optical carrier wave with an extinction rate of 10 dB and at 28 Gbps. The device has been tested by the proposed method at a rate of up to 56 Gbps, and above 28 Gbps the deletion phenomenon still remains, but carrier recovery becomes unviable due to spectral widening, decreased optical carrier relative amplitude and the increase of phase noise. The limitation observed in the reduction in practice occurs due to the finite lifetime of UL-SOA carriers which is of the order of 20 picoseconds for the device used. The use of a shorter carrier life UL-SOA (quantum-dot type UL-SOA) could further increase the maximum utilization rate of the present invention.

Brief Description of the Invention

 The present invention was developed for the purpose of promoting amplitude modulation erasure in optical carriers. For this purpose, an erasing device and an erasing method are proposed which have the advantage of erasing amplitude modulated optical carriers, including extinction ratios greater than 8 dB and at rates exceeding 2 Gbps.

 The erasing device consists of an 8mm ultra-long active cavity semiconductor optical amplifier, electrically divided into four sections of 1-3-3-1mm respectively, which will receive current injection independently.

The proposed deletion method consists of inserting an amplitude modulated optical signal into a linear wavelength SOA, then inserting the signal into a variable polarization controller, and finally inserting the signal into a cavity-containing UL-SOA device. greater than 4 mm in length. In addition, it is proposed an integrated photonic remodulation device whose function is to provide the reuse of amplitude modulated optical carrier in order to erase the original modulation and remodulate the carrier with new amplitude information. The great advantage of this device lies in the fact that it composes a single optical guide, which avoids signal loss in the fiber optic guide and optical fiber guide passage. Another advantage is that the single optical guide eliminates the use of isolators and variable polarization controllers, which reduces system size and reduces equipment costs.

 The integrated photonic remodulation device is based on semiconductor optical amplifiers, preferably designed for gain in wavelengths contained in the telecommunications spectral range. This device contains a full length optical waveguide in which the modulated optical carrier will enter and exit modulated with other information. The device comprises three sections: initial section responsible for preamplifying the amplitude modulated carrier wave, intermediate section responsible for erasing the amplitude modulation information contained in the carrier wave, and final section responsible for remodulating the amplitude optical carrier wave.

 The present invention also contemplates the use of any active cavity semiconductor optical amplifier greater than 4 mm in length to promote erasure in optical carrier waves.

Brief Description of the Figures and Attachments

 The invention will now be described with reference to the accompanying drawings, in which:

 Figure 1 shows a model of the eraser, consisting of an input section (1), two intermediate sections (2 and 3) and a final section (4). Each section has an input port (5, 6, 7, and 8) for current injection.

Figure 2 presents a model of the integrated photonic remodulation device, consisting of a continuous optical waveguide (9), a input section (10), an intermediate section (11), a final section (12), five electrodes (13, 14, 15, 16 and 17) and two electrical isolation channels (18 and 19).

 Figure 3 shows a diagram representing the amplitude modulated optical carrier deletion method and, alternatively, subsequent remodulation thereof. In it, an amplitude digitally modulated optical signal (20) is inserted into a linear semiconductor optical amplifier (21), following a variable polarization controller (22), and finally into a UL-SOA (23) operating at a deep gain saturation, such that its output signal (24) has no different digital levels but maintains considerable continuous power signal. The erased signal (24) may be inserted into a dedicated remodeling device (25) so as to obtain the newly coded channel output (26) in sufficient quality for error free operation.

 Annex 1 shows three diagrams where the left waves represent amplitude modulated optical carrier waves before being erased and the right waves show the waves that were erased by the proposed method, ie with reduced extinction radius. For all cases the carrier wavelength was 1556 nm. In the first diagram a digitally modulated optical signal at a rate of 7 Gbps (27), with an average power of about 200 μνν, few twists and 1000 μνν power (28) are erased; in the second diagram a digitally modulated 7 Gbps rate digitally modulated optical signal and high / low level distortion amplitude noise input (29), with an average power of about 300 μνν, is erased and provides a completely chirp-free signal and power of 1300 μ \ Λ / (30); in the third diagram a 12 Gbps rate digitally modulated optical signal (31), with an average power of about 200 μ \ Ν, is erased and provides signal with some tweeting at amplitude and power of about 3000 μ \ Ν ( 32).

Detailed Description of the Invention This patent application relates to an amplitude modulated carrier wave eraser and an integrated photonic remodeling device, as well as the use thereof for erasing and remodeling respectively. Other objects of this patent application include a method of erasing and the use of the UL-SOA erasing device.

 An object of protection of this invention is an erasing device consisting of a semiconductor optical amplifier characterized by having 8 mm active cavity divided into four sections. The device comprises one 1mm (L1) active cavity inlet section (1), two 3mm (L2) active cavity intermediate sections (2 and 3) each, and one outlet section (4) active cavity 1 mm (L1) long. Each section is characterized by being fed with independent currents through the doors.

 Optimal device operation occurs when the input and output sections operate at the transparency threshold (approximately 1 gain) to minimize the spectral noise level inherent in SOA amplification.

 When the central sections operated at saturated gain the erasure is completely efficient. The first two millimeters of the device act as a quasi-linear preamplifier and the remainder of the cavity as a fully saturated amplifier. This erasing device can be implemented in fully optical processing subsystems, providing miniaturization and overall energy savings.

The injection of current into the device must be such that the total limit of 2.7 Amps is respected. Sections (1) and (4) of regions (A) can be fed with low current to provide unit gain and the eraser to operate as a saturable absorber, thereby helping to suppress spontaneous emission noise ( ASE). Sections (2) and (3) of region B are powered with high current to provide optical gain deeply saturated nonlinear and, consequently, erasure of carrier amplitude modulation.

 Preferably, the injection current percentages in the four sections should be proportional to 12.5% - 37.5% - 37.5% - 12.5%, respectively, in order to maintain an active cavity current density. approximately constant.

 Sections (1) and (4) can also be used as input and output optical signal monitors, providing signal quality analysis without the need for other devices.

 Insulation between sections is possible through the construction of an electrical-insulating channel by bombardment to create an insulating wall or any other microelectronic process to produce insulation between terminals. Importantly, the optical guide cannot be affected by these processes, as the wave must propagate in a continuous guide from the beginning to the end of the device.

 The present invention is also an integrated photonic remodulation device based on semiconductor optical amplifiers, preferably designed for the telecommunications band at 1500 nm or similar wavelength, shown in Figure 2.

 The purpose of this device is to provide amplitude modulated optical carrier reuse (amplitude erasure and remodeling) and can also be used with modulated signal receiver. The device is composed of several semiconductor layers using the technologies of semiconductor optical amplifiers, but highlighting a continuous optical waveguide in all its extension (9). This guide forms the active region through which the modulated optical carrier will enter (10) and exit modulated with other information. This waveguide should be designed to form the active region by injecting convenient electrical current (called polarization current).

The device consists of the following sections: a) Initial section called preamplifier (10) comprising the range from 0.05 to 2.0 mm in length, which has the function of preamplifying the amplitude modulated carrier wave in order to induce optical gain and facilitate saturation of the following sections. Alternatively, by properly electronically switching the bias current, this section can function as a photoreceptor of the modulated signal, allowing the device to receive the information as well. However, sometimes the device will act as drum, sometimes as eraser / remodulator. Simultaneous photo-reception and erasure / remodeling activity will require a strong input signal, as well as the very short section design (11), so that photo-detection attenuates the signal, making it possible to inject a convenient optical carrier in the following section (12);

 b) An intermediate section called UL-SOA (11), comprising a range between 2 mm and 10 mm in length, which has the function of erasing the amplitude modulation information contained in the carrier wave, as well as amplifying the power of this carrier, in order to to enable the reuse of this optical carrier;

 c) Final section called modulator (12) comprising from 0.1 mm to 1 mm in length, which has the function of remodulating the wave in amplitude. Alternatively, this section may be formed by an interferometric guide device known as the Mach-Zehnder modulator, or other integrated device that can modulate the carrier wave being reused.

 The photonic device contains preamplifier / photodetector electrodes (13, 14, 15, 16 and 17) that can polarize the diode formed by the layers just below this electrode either directly (optical amplification function) or reverse polarized (photodetector function). detection).

The UL-SOA electrodes (14, 15 and 16) have the function of directly polarizing the UL-SOA, and the polarization currents may differ for each electrode. For example, a higher current at the start electrode (14) can more quickly saturate UL-SOA, improving the erase function. Figure 2 shows three electrodes on the UL-SOA, however, several can be used so that the maximum number of electrodes would be twenty.

 The modulator electrode 17 is conveniently biased to obtain greater modulation depth and, in addition to the bias direct current, a pulsed current is applied to insert the new modulation containing information to be inserted into the channel. output with the reused carrier. If a Mach-Zehnder modulator is used, several electrodes would be conveniently used on this modulator using the usual procedure for these modulators.

 As the preamplifier, UL-SOA and modulator use different biases, there is a need for electrical isolation between the electrodes of the start, middle and end sections (10, 11 and 12). Normally this electrical isolation is performed by inserting an insulating channel (18) to electrically isolate the section (10) from the section (11). Similarly, the insulating channel (19) has the function of electrically isolating the UL-SOA (11) from the modulator (12).

 Ideally, the active cavity optical guide (9) should be insensitive to the direction of the incident carrier wave bias (vertical or horizontal).

 If this guide cannot be obtained, an adjustable bias controller should be used prior to guide entry, as well as an isolator before and after UL-SOA. In the photonic device of figure 2 an isolator (integrated or discrete) can be used after the optical signal output.

The integrated photonic remodulation device has the advantage of being a single optical guide, which avoids signal loss in the fiber optic guide and optical fiber guide passage. In addition, the single optical guide eliminates the use of an isolator and a polarization controller between the amplifier and UL-SOA. The variable polarization controller would only be necessary if the waveguide was sensitive to light polarization. It is a further object of this invention a deletion method comprising the following steps:

 a) insert, via optical fiber, a carrier wave consisting of an amplitude modulated optical signal (20) such that its wavelength is within the UL-SOA gain region in a linear wandering SOA (21) ), which will act as a linear preamplifier in order to intensify the signal that will later be applied to the UL-SOA;

 b) inserting the signal into a variable polarization controller (22); to obtain a polarization direction signal that maximizes UL-SOA gain.

 c) inserting the signal into a UL-SOA device (23), which is responsible for erasing the carrier wave. The UL-SOA must be polarized with a current high enough to saturate the optical gain of this device.

 In order to reduce spontaneous emission noise (ASE), an optical bandpass filter can be used before and after UL-SOA.

 As the output signal after erasure (24) has no different digital levels and maintains considerable continuous power signal \, it can be inserted into a device dedicated to remodulation (25) so that a signal at the channel output can be obtained. with new coding (26), in good quality.

 The method proposed by this invention differs in that it does not limit the speed expansion of the implemented link and ensures operation for wide diversity of different amplitude modulated channel types that can be efficiently erased and reused.

Additionally, the present invention relates to the use of a semiconductor optical amplifier device characterized by having active cavity greater than 4 mm to promote blanking on amplitude modulated optical carriers. The present invention also relates to the use of the erasure device described above to promote erasure in amplitude modulated optical carriers.

 The present invention also relates to the use of the integrated remodulation device described above to promote amplitude remodulation in optical carriers.

 Annex 1 shows three diagrams showing the deletion of optical carrier waves using the previously proposed method and deletion device. In the diagrams, the left waves represent amplitude modulated optical carrier waves before being erased and the right waves demonstrate the waves that were erased by the proposed method, ie with reduced extinction radius. The insertion of the optical carrier wave was made according to the previously proposed method. For all cases the carrier wavelength was 1556 nm.

 Result 1:

 A 7Gbps digitally amplitude modulated optical signal (27), with an average power of about 200 μ \ Ν, is erased by the payment method of the present invention and provides low-twitter signal and 1000 uW power (28). );

 Result 2:

 A digitally modulated optical signal at 7Gbps rate amplitude and high / low level distortion amplitude noise insertion (29), with an average power of about 300 μ \ Λ, is erased in the proposed system and provides completely free signal. twittering and power of 1300 μ / / (30);

 Result 3:

 A 12 Gbps digitally amplitude modulated optical signal (31), with an average power of about 200 uW, is erased in the proposed system and provides signal with some tweeting in amplitude and power of about 3000 μνν (32).

Claims

1. An eraser device consisting of a semiconductor optical amplifier comprising four sections which will receive current injections independently, as follows:  a) Initial section (1) comprises 1 mm in length, responsible for amplifying the optical carrier wave;  b) Two intermediate sections (2 and 3) with 3 mm each, promote the erasure in optical carrier wave modulation;  c) Final section (4) 1 mm long, characterized by reducing the level of spontaneous emission noise by operation in saturated absorption regime;  2. Multilayer integrated photonic remodulation device using semiconductor optical amplifier technologies characterized by containing five sections that will receive current injections independently, the device comprising:  a) Optical waveguide (9) present throughout the device, responsible for understanding the active region through which the modulated optical carrier will enter;  (b) Initial section (10) comprising a range of 0,05 to 2,0 mm in length, the function of which is to pre-amplify the modulated carrier wave in order to induce optical gain and to facilitate saturation of subsequent sections;  c) Intermediate section (11) comprising a range of 2 mm to 10 mm in length, which has the function of erasing the amplitude modulation information contained in the carrier wave, as well as amplifying the power of the carrier wave; d) Final section (12) comprising a range of 0.1 mm to 1 mm extension, which has the function of remodulating the wave in amplitude. e) Insulating channel (18) in order to electrically isolate the initial section (10) from the intermediate section (11);  f) Insulating channel (19) to electrically isolate the intermediate section (11) from the final section (12);  g) One electrode (13) in the initial section, three electrodes (14,15 and 16) or more in the intermediate section, one electrode in the final section (17).  Device according to Claim 2, characterized in that it contains an end section formed by a Mach-Zehnder modulating interferometric guide.  Device according to claim 2, characterized in that it contains the active cavity optical guide (9) insensitive to the polarization direction of the incident carrier wave.  Device according to claim 2, characterized in that it contains a variable polarization controller before the guide entry, an insulator before the section (11) and another insulator after the section (11).  Device according to claim 2, characterized in that the initial section functions as a photoreceptor of the modulated signal by means of the appropriate electronic switching of the bias current.  7. Method of erasure characterized by comprising the following steps:  (a) fiber optically inserting a carrier wave consisting of an amplitude modulated optical signal (20) into a linear SOA (21) such that the wavelength of this carrier is within the UL-SOA gain region;  b) Insert the signal into a variable bias controller (22) so that carrier wave biasing maximizes ULSOA gain c) Insert the signal into a UL-SOA device (23), which should be saturated by current injection. Method according to claim 4, characterized in that the device described in claim 1 may optionally be used in place of the UL-SOA device.  Method according to claim 4, characterized in that it optionally inserts the signal into an optical bandpass filter before and after the UL-SOA device.  Use of the device described in claim 1 characterized in that it promotes the erasure of amplitude modulated optical carrier waves.  Use of the device described in claim 2 characterized in that it enables simultaneous photo reception and erasure / remodeling activity.  12. Use of a semiconductor optical amplifier with an optical active cavity greater than 4 mm characterized in that it provides for the erasure of amplitude modulated optical carrier waves.  Use of the photonic remodulator device described in claim 2 for promoting remodulation of amplitude modulated optical carrier waves.