Patent Application
20190312646
The invention relates to optical fiber communications apparatus and methods of use thereof.
This section introduces aspects that may be help to facilitate a better understanding of the inventions. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is prior art or what is not prior art.
In optical fiber communication, wavelength division multiplexing (WDM) has been an important method for increasing the data capacity of an optical fiber. WDM has also stimulated the development of various wavelength selective apparatus such as wavelength-channel based optical switches, optical add-drop multiplexers, optical cross-connects, and wavelength-channel-based optical wavelength-multiplexers and optical wavelength-demultiplexers. WDM has also stimulated a development of optical amplifiers over broad wavelength bands.
Presently, WDM optical amplifiers typically have low wall plug power efficiencies. The inventor believes that some embodiments may improve the wall plug power efficiencies of some such optical amplifiers to greater than 10 percent and possibly to even greater than 20 percent. In such embodiments, the optical amplifiers are pre-amplifiers for optical sources of multi-wavelength-channel carrier light, which may also have wavelength-dependent intensity pre-compensation.
In some embodiments, an apparatus includes an optical source to produce light, e.g., temporally in parallel, in a sequence of wavelength-channels, an optical transmission fiber connected to receive said produced light, an optical wavelength-demultiplexer optically coupled to the optical transmission fiber, and an array of optical data modulators. Each of the optical data modulators is optically coupled to receive light of a corresponding one of the wavelength-channels from the optical source via the optical transmission fiber and the optical wavelength-demultiplexer. The optical source is configured to transmit said light to said optical transmission fiber with a wavelength-dependent intensity.
In some such embodiments of the apparatus, the wavelength-dependent intensity may be largest for one of the wavelength channels near an edge of a wavelength range for the sequence of wavelength-channels. The wavelength-dependent intensity may even be largest for wavelength-channels near one or both edges of the wavelength range.
In any of the above embodiments, the apparatus may further include an array of optical data receivers, wherein an optical fiber couples to the array of optical data receivers via a second optical wavelength-demultiplexer and couples to the array of optical data modulators via an optical wavelength-multiplexer. In some such embodiments, the optical fiber coupled to the array of optical data receivers via the second optical wavelength-demultiplexer is the same optical transmission fiber. In any embodiments of this paragraph, light received at the array of optical data receivers may have a substantially flat wavelength-channel dependent intensity. In any embodiments of this paragraph, the optical source may be configured to substantially or, at least, partially, pre-compensate for wavelength-dependent optical attenuation between the optical source and the array of optical data receivers.
In any of the above embodiments, the apparatus may further include an optical amplifier located to amplify light output from the optical source and transmit said amplified light to the optical transmission fiber with a wall plug power efficiency of greater than 10 percent or even possibly greater than 20 percent.
In any of the above embodiments with an optical amplifier, the optical amplifier may additionally share the multi-wavelength optical source among multiple transmission fiber links by splitting the power of the multi-wavelength optical source into separate portions and amplifying each such portion prior to transmission to the corresponding transmission fiber link.
In any of the above embodiments, the optical source may include an array of lasers optically connected to inputs of an optical wavelength-multiplexer. Each of the lasers may be configured to produce light of different wavelength-channel. Different ones of the lasers may be configured to be driven such that, at an output of the optical wavelength-multiplexer, the light of wavelength-channels near outer boundaries of the sequence may have a higher intensity than light of wavelength-channels away from the boundaries. Some such embodiments of this paragraph may further include an optical amplifier connected to amplify light output from the array of lasers and to transmit said amplified light to the optical transmission fiber with a wall plug power efficiency of greater than 10 percent or even possibly greater than 20 percent.
In any of the above embodiments, the apparatus may be a wavelength division multiplexing, optical communication system communicatively connecting digital data servers located inside a data center.
In some of the above embodiments, the optical data modulators may be configured to transmit data-modulated light to the optical transmission fiber.
In other embodiments, a method, includes, from a multi-wavelength optical source, transmitting to an optical transmission fiber light with a wavelength-dependent intensity to, at least, partially compensate for a wavelength-dependent optical attenuation between the multi-wavelength optical source and optical data receivers of an array. Each of said optical data receivers is connected via the optical transmission fiber to receive some light of a corresponding wavelength-channel of said transmitted light.
In some of the embodiments, the above method may further include, at each one of a plurality of optical data modulators, data modulating light received from the multi-wavelength optical source in a wavelength-channel corresponding to said one of the optical data modulators, wherein the optical data modulators of the plurality are connected to receive light from said multi-wavelength optical source via a same optical fiber.
In some of the embodiments of the method, each one of said optical data receivers may be connected to receive a portion of the data-modulated light from a different corresponding one of the optical data modulators, wherein the array of optical data modulators is connected to transmit the data-modulated light to a same optical fiber. In some such embodiments, the method may further include, at the optical source, adjusting a wavelength dependence of said intensity of transmitted light, at least, in part based on measurements of light intensities received at some of the optical data receivers.
In any of the embodiments of the method, the wavelength-dependent intensity of the transmitted light may be largest for one or both of the wavelength-channels near an edge of an interval including the sequence of wavelength-channels.
In any of the embodiments of the method, the wavelength-dependent intensity of the transmitted light may have maxima in the wavelength-channels near one or both edges of an interval including the sequence of wavelength-channels.
Various embodiments include methods of operating the above described embodiments of apparatus.
In the Figures, relative dimension(s) of some feature(s) may be exaggerated to more clearly illustrate the feature(s) and/or relation(s) to other feature(s) therein.
In the various Figures, similar reference numbers may be used to indicate similar structures and/or structures with similar functions.
Herein, various embodiments are described more fully by the Figures and the Detailed Description of Illustrative Embodiments. Nevertheless, the inventions may be embodied in various forms and are not limited to the embodiments described in the Figures and the Detailed Description of Illustrative Embodiments.
An optical source cable of outputting light of different optical wavelength-channels, in parallel, is also often referred to as an optical comb source.
Some embodiments of the present application may be able to use some apparatus and/or methods disclosed in one or more of the below-listed U.S. patent applications:
U.S. application Ser. No. 15/946,161, filed Apr. 5, 2018, by Ting-Chen Hu et al;
U.S. application Ser. No. 15/946,061, filed Apr. 5, 2018, by Mark Earnshaw et al;
U.S. application No. Ser. 15/946,353, filed Apr. 5, 2018, by Yee Low et al; and
U.S. provisional application No. 62/653,152, filed Apr. 5, 2018, by David Neilson et al. Each of the above-listed U.S. applications is incorporated herein, by reference, in its entirety.
In a WDM optical fiber communication system various optical components can attenuate or amplify light of different wavelength-channels to different amounts. On the other hand, it may be desirable to have optical data receivers of light for different wavelength-channels to receive data-modulated optical carriers of about the same time-averaged intensity. For example, such received time-averaged intensities may desirably vary by less than about 3 decibels, less than about 2 decibels or even by less than about 1 decibel over an array of optical data receivers for the different WDM wavelength-channels. In such a situation, the different optical data receivers are more likely to have similar bit error rates during demodulation of data from the received data-modulated optical carriers without a need for individualization of such receivers or with a need of less complex individualization thereof.
In many situations, the overall energy efficiency of a system is often an important metric. Therefore, it may be advantageous to approximately minimize the optical power at each optical data receiver to be near a minimum required for obtaining an acceptable transmission bit error rate given the sensitivity of the optical data receiver. For this reason, it may be desirable to have optical data receivers of different optical wavelength-channels to receive data-modulated optical carriers of about the same time-averaged intensity.
The inventor believes that some WDM optical fiber communication systems may be improved by pre-compensating the intensity of multi-wavelength carrier light, in a wavelength-dependent manner, prior to its transmission to optical components that can cause wavelength-dependent optical attenuation and/or optical amplification, e.g., prior to transmission to an optical transmission fiber for carrying such WDM carrier light and possibly prior to transmission of such WDM carrier light to an optical pre-amplifier. Such wavelength-dependent intensity pre-compensation may lower undesired effects of accumulated wavelength-dependent optical attenuation.
Also, such pre-compensation may improve the efficiency of any optical pre-amplifier for multi-wavelength-channel light, e.g., when a multi-wavelength-channel data-modulated optical signal is transmitted between one optical data transmitter and one optical data receiver.
Indeed, such pre-compensation may be especially useful in WDM optical fiber communication systems, which are based on a multi-wavelength optical source whose power is distributed in a wavelength-dependent manner to optical data modulators for use in sets of optical communication paths that rarely change over time. Such sets of optical communication paths may be used, for example, in some types of intra-data center, optical fiber communication.
As illustrated, the multi-wavelength optical source 12 may include, in some embodiments, N single wavelength-channel, light sources 121, 122, . . . , 12N, e.g., N lasers, and an optical wavelength-multiplexer 14 to combine the light output by the single wavelength-channel, light sources 121-12N. The optical output of the optical wavelength-multiplexer optically couples to one end of the optical transmission fiber 18, e.g., a standard single-mode optical fiber. The individual light source 121-12N may be pumped, e.g., current pumped, in a manner that causes a desired wavelength-dependent intensity in the produced multi-wavelength-channel carrier light, e.g., a wavelength-dependent intensity pre-compensation.
Herein, carrier light is either unmodulated or modulated at a rate that is, at least, orders of magnitude lower than a symbol rate of subsequent modulation thereof.
In some embodiments, the multi-wavelength optical source 12 may optionally include an optical amplifier 16, e.g., an erbium-doped-fiber optical amplifier. The optical amplifier optically pre-amplifies the carrier light of the set of N wavelength-channels λ1-λN, as received from the optical wavelength-multiplexer 14, i.e., prior to transmission of said multiple wavelength-channel, carrier light to the optical transmission fiber 18. A suitable wavelength-dependent pre-compensation of said carrier light may substantially improve the power efficiency of the optical amplifier 16. For example, the inventor believes that a suitable pre-compensation may improve the wall plug power efficiencies of some forms of the optical amplifier 16 to greater than 10 percent and possibly to even greater than 20 percent.
The array of optical data modulators 221-22N is optically coupled to receive light from the multi-wavelength optical source 12 from the other end of the optical transmission fiber 18 via an optical wavelength-demultiplexer 20. In particular, each optical data modulator 221-22N is optically coupled to an optical output of the optical wavelength-demultiplexer 20, which corresponds to one of the wavelength-channels λ1-λN. The light of the wavelength-channels λ1-λN XN is optical carrier light, onto which, the optical data modulators 221-22N are configured to modulate data streams for optical transmission therefrom. That is, each optical data modulator 221-22N data-modulates received carrier light of a corresponding one of the wavelength-channels λ1-λN. The centralized multi-wavelength optical source 12 provides the carrier light for the array of N individual optical data modulators 221-22N, e.g., to modulate N independent data streams on the N different wavelength-channels thereof.
As illustrated in
The WDM communication system 10 has several optical components that typically cause wavelength-dependent intensity filtering of light therein. For example, the optical wavelength-multiplexers 14, 24; the optical wavelength-demultiplexers 20, 28; and the optical amplifier 16 can all cause wavelength-dependent intensity filtering and wavelength dependent gain. For example, the optical amplifier 16 can also have a wavelength-dependent optical gain spectrum. For these reasons, the WDM light can have a different wavelength-dependent intensity at the input to the optical transmission fiber 18, and at the array of optical data receivers 301-30N. At the array of optical data receivers 301-30N such a wavelength-dependent passive and/or active optical intensity filtering could be problematic in the absence of some type of compensation.
The WDM communication system 10 may be advantageously configured to, at least, partially pre-compensate such an accumulation of wavelength-dependent attenuation due to transmission of said WDM carrier light between the multi-wavelength optical source 12 and the array of optical data receivers 301-30N .
For example, the time-averaged intensity of received light may desirably vary, in a wavelength-dependent manner, over the array of optical data receivers 301-30N by less than about 3 decibels, by less than about 2 decibels, or even by less than about 1 decibel. In such a situation, the different optical data receivers 301-30N are more likely to have similar bit error rates during the demodulation of data from the different received data-modulated optical carriers without a need for substantial individualization of said optical data receivers 301-30N or with a need of less complex individualization thereof.
In various embodiments, the wavelength-dependence of the intensity of the light received at the array of optical data receivers 301-30N may be less than for the multi-wavelength light transmitted to the optical transmission fiber 18 by the multi-wavelength optical source 12. Herein, the embodiments are meant to cover apparatus and methods for pre-compensation of wavelength-dependent intensities to reduce various quantitative measures of such wavelength-dependency for the light intensity at the array of optical data receivers 301-30N as compared to the wavelength-dependency of the intensity of the light transmitted to the input end of the optical transmission fiber 18.
The optical communication system 10′ also includes an optical rotator 2, which operates to separately route data-modulated and data-unmodulated light in location 4. In particular, the optical rotator 2 directs unmodulated or substantially unmodulated light of the N optical wavelength channels λ1-λN from the optical comb source 12 to the optical transmission fiber 18, for transmission to the location 6. Also, the optical rotator 2 directs data-modulated light on the N optical wavelength-channels received from the remote location 6, i.e., via the optical transmission fiber 18, to the input of the optical wavelength-demultiplexer 28 via another optical fiber OF.
The method 40 includes, at a multi-wavelength optical source, transmitting to an optical transmission fiber carrier light with a wavelength-dependent, intensity to substantially pre-compensate or , at least, to partially pre-compensate for wavelength-dependent optical attenuation between the multi-wavelength optical source and optical data receivers of an array (step 42). For example, the optical source may be the optical source 12 of
The method may further include, at each one of the optical data modulators of an array, e.g., at the optical data modulators 101-10N of
Typically, each of the N optical data receivers is optically coupled to receive a portion of the data-modulated light from a different corresponding one of the optical data modulators of the array. The array of optical data modulators is connected to transmit the data-modulated light to the same optical fiber for transmission to the corresponding optical data receivers.
The method 40 may further include, at the multi-wavelength optical source, adjusting a wavelength-dependency of the intensity of the transmitted carrier light, at least, in part based on measurements of intensities of received light at some of the optical data receivers (step 46). The measurements may characterize a wavelength-dependency of said received light over the array of optical receivers, e.g., as measured by separate optical intensity monitors or optical data detectors in the optical data receivers or by a received signal strength indicator (RSSI) typically incorporated into the electronic amplifier connecter to a high-speed receiver photodiode. The wavelength dependency may also be characterized by a measurement of photocurrent generated in the modulators of the multi-wavelength transmitter if a modulation approach such as electro-absorption or another effect that generates a photocurrent sufficient to measure the differential optical wavelength strengths. The information about the required pre-compensation can be returned to the start of the transmission link by multiple methods but preferentially by back propagation as low speed tone modulation outside the optical data bandwidth. At the multi-wavelength optical source, the wavelength-dependency may also be partially preset based on known characteristics of the WDM optical fiber communication system. Such feedback adjustment may be made, e.g., to substantially or partially compensate for wavelength-dependent optical attenuation between the optical source and the array of optical data receivers. Pre-compensation may not achieve a fully optimized spectrum shaping or overall efficiency but does not necessarily require an added back propagation channel, e.g., for measurements from optical data receivers or an optical amplifier.
In any of the embodiments of the method 40, the wavelength-dependent intensity of the WDM carrier light, transmitted from the multi-wavelength optical source, may be largest for one of the wavelength-channels near an edge of an interval including the sequence of optical wavelength-channels.
In any of the embodiments of the method 40, the wavelength-dependent intensity of the WDM carrier light, transmitted from the multi-wavelength optical source, may have maxima in wavelength-channels near both edges of an interval including the sequence of wavelength-channels.
The Detailed Description of the Illustrative Embodiments and drawings merely illustrate principles of the inventions. Based on the present specification, those of ordinary skill in the relevant art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the inventions and are included within the scope of the claims. Also, statements herein reciting principles, aspects, and embodiments are intended to encompass equivalents thereof.
This application claims the benefit of U.S. provisional patent application No. 62/653,551, filed on Apr. 5, 2018, by Mark P. Earnshaw.
| Number | Date | Country | |
|---|---|---|---|
| 62653551 | Apr 2018 | US |
