Patent Application
20210247564
The present disclosure relates to optical fibers and in particular relates to low loss and low dispersion optical fibers for data centers.
The rapid growth of Internet applications have driven the optical network evolution for data centers, from 10 Gb/s optical systems in 2007 to the current/upcoming 400 Gb/s systems. Proliferation of social media and video streaming demands 400G networks. In the future, industry trends show that Internet of things (IoT) and machine learning based applications will require much more communication among massive number computers/servers, leading to stringent requirements on network capacity and efficiency.
The first challenge is to achieve high transmission capacity. For the past decade from 10G to 400G, various communication technologies have been selected based on technical feasibility as well as economic considerations. For intra-data center applications, optical systems have evolved in multiple aspects, including (i) symbol rate from 10 Gbaud to 25 Gbaud, (ii) modulation format from non-return-to-zero (NRZ) to pulse-amplitude modulation (PAM4), (iii) using coarse wavelength-division multiplexing (WDM) and parallel fibers, and (iv) using multimode fiber (MMF) and single mode fiber (SMF). For future data center interconnects (DCI), optical systems will employ coherent communication technologies and dense WDM (DWDM) with symbol rates increasing from 28 Gbaud to 60 Gbaud and modulation formats including quadrature phase shift keying (QPSK) and 16ary quadrature amplitude modulation (16-QAM). For future generations of 800G and 1.6T systems, a combination of different methods are required including increasing baud rate and modulation order, and adding more parallel lanes. There is a trend that coherent communication technologies are likely to be applied to intra-data center systems to increase capacity. Also, for DCI links, probabilistic constellation shaping (PCS) technology is very likely to be adopted. PCS provides both higher data capacity and finer data rate granularity and has been already implemented in a few commercial transponders.
A second significant challenge is to reduce the power consumption of optical transceivers. Due to the massive number of connections, network switches for within and between data centers need to accommodate a large number of optical transceivers. High port density in network switches is important to reducing system complexity and cost. This leads to rigorous restrictions on transceiver form factors, and therefore demanding heat dissipation challenges for transceivers. The current/upcoming 400G optical transceivers use octal small form factor pluggable (OSFP) and quad small form factor pluggable-double density (QSFP-DD). It is desired to limit transceiver power consumption to 15 W or less. The power consumption of a coherent transceiver results primarily from digital signal processing (DSP) and also from lasers, photodetector, amplifiers, modulators, digital-to-analogue converter, and analogue-to-digital converter. DSP power consumption is mainly from forward error correction (FEC), chromatic dispersion (CD) compensation, and polarization mode demultiplexing (PMD). One way to increase transceiver power efficiency is to use complementary metal-oxide-semiconductor (CMOS) technology with a fine feature size such as 7 nm, so that the entire DSP power is reduced. Industry trends shows that 7 nm CMOS technology will be used in 400G and higher data rate transceivers.
Accordingly, the inventors have provided a low loss and low dispersion optical fiber to increase data capacity and to reduce DSP power consumption for intra- and inter-data center optical interconnection systems.
In some embodiments, a data center optical communications system includes: a transmitter comprising a light source, wherein the light source is configured to provide light; an optical fiber operably connected to said transmitter and configured to receive light from the light source, wherein the optical fiber has a length L of 50 km or greater; a receiver configured to receive light from the optical fiber, wherein the receiver includes a detector for detecting the light, wherein the system has a power consumption of 15 W or less.
Other and further embodiments of the present disclosure are described below.
Embodiments of the present disclosure, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the disclosure depicted in the appended drawings. However, the appended drawings illustrate only typical embodiments of the disclosure and are therefore not to be considered limiting of scope, for the disclosure may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
Reference is now made in detail to various embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same or like reference numbers and symbols are used throughout the drawings to refer to the same or like parts. The drawings are not necessarily to scale, and one skilled in the art will recognize where the drawings have been simplified to illustrate the key aspects of the disclosure. The claims as set forth below are incorporated into and constitute part of this Detailed Description.
In this document, relational terms, such as first and second, top and bottom, and the like, are used solely to distinguish one entity or action from another entity or action, without necessarily requiring or implying any actual such relationship or order between such entities or actions.
It will be understood by one having ordinary skill in the art that construction of the described disclosure, and other components, is not limited to any specific material. Other exemplary embodiments of the disclosure disclosed herein may be formed from a wide variety of materials, unless described otherwise herein.
As used herein, the term “about” means that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art. When the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. Whether or not a numerical value or end-point of a range in the specification recites “about,” the numerical value or end-point of a range is intended to include two embodiments: one modified by “about,” and one not modified by “about” It will be further understood that the end-points of each of the ranges are significant both in relation to the other end-point, and independently of the other end-point.
“Radial position” and/or “radial distance,” when used in reference to the radial coordinate “r” refers to radial position relative to the centerline (r=0) of the central core portion in the optical fiber.
The length dimension “micrometer” may be referred to herein as micron (or microns) or μm.
The “refractive index profile” is the relationship between refractive index or relative refractive index and radial distance r from the core portion's centerline. For relative refractive index profiles depicted herein as relatively sharp boundaries between various regions, normal variations in processing conditions may result in step boundaries at the interface of adjacent regions that are not sharp. It is to be understood that although boundaries of refractive index profiles may be depicted herein as step changes in refractive index, the boundaries in practice may be rounded or otherwise deviate from perfect step function characteristics. It is further understood that the value of the relative refractive index may vary with radial position within the core region and/or any of the cladding regions. When relative refractive index varies with radial position in a particular region of the fiber (core region and/or any of the cladding regions), it may be expressed in terms of its actual or approximate functional dependence or in terms of an average value applicable to the region. Unless otherwise specified, if the relative refractive index of a region (core region and/or any of the inner and/or common cladding regions) is expressed as a single value, it is understood that the relative refractive index in the region is constant, or approximately constant, and corresponds to the single value or that the single value represents an average value of a non-constant relative refractive index dependence with radial position in the region. Whether by design or a consequence of normal manufacturing variability, the dependence of relative refractive index on radial position may be sloped, curved, or otherwise non-constant.
Unless stated otherwise, the “relative refractive index percent” is defined as Δ%=100×(ni2−nc2)/2ni2, and as used herein nc is the average refractive index of undoped silica glass. As used herein, the relative refractive index is represented by Δ and its values are given in units of “%”, unless otherwise specified. The terms: relative refractive index percent, relative refractive index, refractive index delta, refractive index, relative refractive index delta, delta, Δ, Δ %, % Δ, delta %, % delta and percent delta may be used interchangeably herein. In cases where the refractive index of a region is less than the average refractive index of undoped silica, the relative index percent is negative and is referred to as having a depressed region or depressed index. In cases where the refractive index of a region is greater than the average refractive index of the cladding region, the relative index percent is positive. An “updopant” is herein considered to be a dopant which has a propensity to raise the refractive index relative to pure undoped SiO2. A “downdopant” is herein considered to be a dopant which has a propensity to lower the refractive index relative to pure undoped SiO2. Examples of updopants include GeO2 (germania), Al2O3, P2O5, TiO2, Cl, and/or Br. Examples of downdopants include fluorine and B2O3. As described herein, while the relative refractive index of the optical profiles are calculated where index of n is undoped silica, the entire index profile of the optical fiber can be shifted linearly up (or down) in order to obtain equivalent optical fiber properties.
The “effective area” can be defined as:
where f(r) is the transverse component of the electric field of the guided optical signal and r is radial position in the fiber. “Effective area” or “Aeff” depends on the wavelength of the optical signal. Specific indication of the wavelength will be made when referring to “Effective area” or “Aeff” herein. Effective area is expressed herein in units of “μm2”, “square micrometers”, “square microns” or the like.
“Chromatic dispersion,” herein referred to as “dispersion” unless otherwise noted, of an optical fiber is the sum of the material dispersion, the waveguide dispersion, and the intermodal dispersion. “Material dispersion” refers to the manner in which the refractive index of the material used for the optical core affects the velocity at which different optical wavelengths propagate within the core. “Waveguide dispersion” refers to dispersion caused by the different refractive indices of the core and cladding of the optical fiber. In the case of single mode waveguide fibers, the inter-modal dispersion is zero. Dispersion values in a two-mode regime assume intermodal dispersion is zero. The zero dispersion wavelength (λ0) is the wavelength at which the dispersion has a value of zero. Dispersion slope is the rate of change of dispersion with respect to wavelength. Dispersion and dispersion slope are reported herein at a wavelength of 1310 nm or 1550 nm, as noted, and are expressed in units of ps/nm/km and ps/nm2/km, respectively. Chromatic dispersion is measured as specified by the IEC 60793-1-42:2013 standard, “Optical fibres—Part 1-42: Measurement methods and test procedures—Chromatic dispersion.”
The cutoff wavelength of an optical fiber is the minimum wavelength at which the optical fiber will support only one propagating mode. For wavelengths below the cutoff wavelength, multimode transmission may occur and an additional source of dispersion may arise to limit the fiber's information carrying capacity. Cutoff wavelength will be reported herein as a cable cutoff wavelength. The cable cutoff wavelength is based on a 22-meter cabled fiber length as specified in TIA-455-80: FOTP-80 IEC-60793-1-44 Optical Fibres—Part 1-44: Measurement Methods and Test Procedures—Cut-off Wavelength (21 May 2003), by Telecommunications Industry Association (TIA).
The term “attenuation,” as used herein, is the loss of optical power as the signal travels along the optical fiber. Attenuation is measured as specified by the IEC 60793-1-40:2019 standard entitled “Optical fibers—Part 1-40: Attenuation measurement methods.”
The mode field diameter (MFD) is measured using the Petermann II method and was determined from:
where f(r) is the transverse component of the electric field distribution of the guided light and r is the radial position in the fiber. Unless otherwise specified, “mode field diameter” or “MFD” refers to the mode field diameter at 1310 nm.
Returning to
Receiver 104 receives the optical signal from optical fiber 106. Receiver 104 includes a detector, such as a photodetector, that provides an output characteristic of the optical signal. The detector is responsive to the wavelength(s) of the optical signal. The detector may convert the optical signal to an electrical signal having a current or voltage proportional to or otherwise characteristic of the optical signal. In one embodiment, receiver 104 is implemented as a chip, such as a silicon chip compatible with the silicon photonics technology platform. The receiver 104 may receive the signal directly from optical fiber 106 or indirectly from optical fiber 106 via a waveguide (e.g. an on-chip waveguide).
The optical fiber 106 is interconnected with transmitter 102 and receives the optical signal produced by the light source. The optical fiber 106 delivers the optical signal to receiver 104. The optical fiber 106 may be a single mode fiber or a multimode fiber. In one embodiment, the optical fiber 106 is a silica-based fiber that includes a higher index silica-based core and a lower index silica-based cladding.
A schematic cross-sectional depiction of an optical fiber used in the exemplary optical fiber data communications system (“system”) 100a, 100b, 100c is further described below and shown in
Referring again to
In the embodiments depicted in
Referring again to
Further, the low loss dispersion limiting optical fiber 200 comprises a relative refractive index change Δ between the core 202 and the cladding 204 of from about 0.3 to about 0.8, where Δ=Δ1−Δ2. As non-limiting examples, the refractive index change Δ may be from about 0.4 to about 0.7, 0.5 to about 0.65, or the like, for example, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, or the like. Further, including a dopant in the core 202, the cladding 204, or both, (e.g., an updopant or a downdopant) may alter the relative refractive index between the core 202 and the cladding 204, i.e. alter the refractive index change Δ. As used herein, an “updopant” is a dopant which has a propensity to raise the refractive index relative to pure undoped SiO2 and a “downdopant” is a dopant which has a propensity to lower the refractive index relative to pure undoped SiO2.
Referring still to
Further, when one or more photons comprising a wavelength of about 1550 nm propagate along the optical fiber 200, the optical fiber 200 induces an effective area of from about 30 μm2, to about 70 μm2, for example, about 35 μm2 to about 60 μm2, about 40 μm2 to about 55 μm2, from about 45 μm2 to about 50 μm2, or the like, such as 30 μm2, 35 μm2, 40 μm2, 45 μm2, 50 μm2, 55 μm2, 60 μm2, 65 μm2, 70 μm2, 75 μm2, 80 μm2, or the like. While not intending to be limited by theory, the effective area is the cross-sectional area over which the energy of the electric field of the fundamental mode of light propagating along the optical fiber 200 is distributed within the core 202. For example, the effective area of a single mode optical fiber is related to the maximum energy the core 202 can carry without inducing non-linear type signal penalties.
Referring still to
Further, when one or more photons comprising a wavelength of about 1550 nm propagate along the optical fiber 200, the optical fiber 200 induces a dispersion slope of from about 0.05 ps/nm2/km to about 0.055 ps/nm2/km, for example, about 0.051 ps/nm2/km to about 0.054 ps/nm2/km, such as about 0.0515 ps/nm2/km, 0.0516 ps/nm2/km, 0.0518 ps/nm2/km, 0.052 ps/nm2/km, 0.0521 ps/nm2/km, 0.0525 ps/nm2/km, 0.053 ps/nm2/km, 0.0535 ps/nm2/km, 0.0538 ps/nm2/km or the like. While not intending to be limited by theory, the dispersion slope is the rate at which the absolute dispersion rate changes with wavelength. Smaller dispersion slope may be desired for flat dispersion over a wide wavelength window. Moreover, when one or more photons comprising a wavelength of about 1550 nm propagate along the optical fiber 200, optical fiber 200 induces an attenuation rate of about 0.175 dB/km or less, for example, about 0.17 dB/km or less about 0.165 dB/km or less, such as about 0.16 dB/km, 0.155 dB/km, 0.15 dB/km, 0.14 dB/km, 0.13 dB/km, 0.12 dB/km, or the like. While not intending to be limited by theory, the attenuation rate is rate of intensity loss (e.g., photon loss) of a plurality of photons propagating along the optical fiber 200.
Table 1 below lists attributes of examples of the optical fiber 200 of
Referring now to
Referring still to
Further, n1>n3>n4>n2 and Δ1>Δ3>Δ4>Δ2. As stated above, the core 202 may be pure silica glass or glass doped with Cl, or K, or F for low loss. As non-limiting examples, the relative refractive index Δ1 may be from about −0.1 to about 0.2, for example, −0.1, −0.05, 0, 0.05, 0.1, 0.15, or the like. The first cladding portion 204a, the cladding ring 206 and the second cladding portion 204b may each comprise glass (e.g., silica glass) doped with F for lowering their respective refractive indices. As non-limiting examples, the relative refractive index Δ2 may be from about −0.2 to about −0.7, or the like, for example, −0.25, 0.3, 0.35, −0.45, −0.5, −0.55, −0.6, −0.65, or the like. As non-limiting examples, the relative refractive index Δ3 may be from about −0.1 to about −0.5, or the like, for example, −0.15, −0.2, −0.25, −0.3, −0.35, −0.4, −0.45, or the like. As non-limiting examples, the relative refractive index Δ4 may be from about −0.2 to about −0.6, or the like, for example, −0.25, 0.3, 0.35, −0.45, −0.5, −0.55, −0.6, or the like.
The optical fiber 300 comprises a refractive index change Δ′ between the core 202 and the first cladding portion 204a of from about 0.2 to about 0.6, where Δ′=Δ1−Δ2. In some embodiments, the refractive index change Δ′ may be from about 0.4 to about 0.5, for example, 0.25, 0.3, 0.35, 0.4, 0.41, 0.43, 0.45, 0.47, 0.49, 5, 5.5, or the like. The optical fiber 300 also comprises a refractive index change Δ″ between the first cladding portion 204a and the cladding ring 206 of from about 0 and about 0.2 (i.e. the refractive index of the cladding ring 206 may be higher than the refractive index of the first cladding portion 204a), where Δ″=Δ3−Δ2. In some embodiments, the refractive index change Δ″ may be about 0.02, 0.05, 0.1, 0.12, 0.15, 0.18, or the like. Moreover, the optical fiber 300 comprises a refractive index change Δ′″ between the first cladding portion 204a and the second cladding portion 204b of from about 0 to about 0.1 (i.e. the refractive index of the second cladding portion 204b may be higher than the refractive index of the first cladding portion 204a), where Δ′″=Δ4−Δ2. In some embodiments, the refractive index change Δ′″ may be about −0.02, −0.04, −0.05, −0.1, or the like.
The optical fiber 300 may comprise a cutoff wavelength of about 1600 nm or less, 1500 nm or less, 1350 nm or less, or the like, for example, 1550 nm, 1516 nm, 1500 nm, 1464 nm, 1450 nm, 1403 nm, 1400 nm, 1384 nm, 1350 nm, 1300 nm, 1250 nm, 1200 nm, 11150 nm, 1100 nm, 1050 nm, 1000 nm, 950 nm, 900 nm, 850 nm, 800 nm, or the like. Further, when one or more photons comprising a wavelength of about 1550 nm propagate along the optical fiber 300, the optical fiber 300 induces a mode field diameter of a photon comprising a wavelength of about 1550 nm of from about 8 μm to about 12 μm, for example, about 9 μm to about 11 μm, 9.5 μm to about 10.5 μm, or the like, such as 8 μm, 8.5 μm, 9 μm, 9.5 μm, 9.9 μm, 10 μm, 10.1 μm, 10.2 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or the like.
Further, in some embodiments, when one or more photons comprising a wavelength of about 1550 nm propagate along the optical fiber 300, the optical fiber 300 induces an effective area of from about 50 μm2 to about 100 μm2, 60 μm2 to about 90 μm2, 70 μm2 to about 80 μm2, or the like, such as 50 μm2, 55 μm2, 60 μm2, 65 μm2, 70 μm2, 73.5 μm2, 74.3 μm2, 75 μm2, 76.8 μm2, 78.7 μm2, 80 μm2, 85 μm2, 90 μm2, 95 μm2, 100 μm2, or the like. Further, when one or more photons comprising a wavelength of about 1550 nm propagate along the optical fiber 300, the optical fiber 300 induces dispersion at an absolute dispersion rate of about 9 ps/nm/km or less, for example about 8.6 ps/nm/km or less, 8.5 ps/nm/km or less, 8 ps/nm/km or less, 7.5 ps/nm/km or less, 7 ps/nm/km or less, 6.5 ps/nm/km or less, 6 ps/nm/km or less, 5.7 ps/nm/km or less, 5.5 ps/nm/km or less, 5 ps/nm/km or less, 4.5 ps/nm/km or less, 4.5 ps/nm/km or less, 4 ps/nm/km or less, 3.8 ps/nm/km or less, 3.6 ps/nm/km or less, 3.5 ps/nm/km or less, 3 ps/nm/km or less, 2.5 ps/nm/km or less, 2 ps/nm/km or less, 1.5 ps/nm/km or less, 1.1 ps/nm/km or less, 1 ps/nm/km or less, 0.5 ps/nm/km or less, 0.1 ps/nm/km or less, or the like.
In some embodiments, when one or more photons comprising a wavelength of about 1550 nm propagate along the optical fiber 300, the optical fiber 300 induces dispersion at a dispersion slope of from about 0.05 ps/(nm2)km to about 0.1 ps/(nm2)km, 0.055 ps/(nm2)km to about 0.085 ps/(nm2)km, or the like, such as about 0.0525 ps/(nm2)km, 0.055 ps/(nm2)km, 0.0564 ps/(nm2)km, 0.0575 ps/(nm2)km, 0.06 ps/(nm2)km, 0.0625 ps/(nm2)km, 0.0645 ps/(nm2)km, 0.065 ps/(nm2)km, 0.0675 ps/(nm2)km, 0.0676 ps/(nm2)km, 0.07 ps/(nm2)km, 0.0725 ps/(nm2)km, 0.075 ps/(nm2)km, 0.0775 ps/(nm2)km, 0.08 ps/(nm2)km, 0.0825 ps/(nm2)km, 0.0834 ps/(nm2)km, 0.085 ps/(nm2)km, or the like.
Moreover, when one or more photons comprising a wavelength of about 1550 nm propagate along the optical fiber 300, the optical fiber 300 induces attenuation at an attenuation rate of about 0.175 dB/km or less, for example, 0.17 dB/km or less, about 0.165 dB/km or less, such as about 0.16 dB/km, 0.155 dB/km, 0.15 dB/km, 0.14 dB/km, 0.13 dB/Km, 0.12 dB/km, or the like.
Table 2, below, lists attributes of example optical fiber 300.
Existing optical systems for data centers usually use standard single mode fiber. Typically, low fiber loss has small impact on data capacity for short reach systems (e.g. 50 km to 150 km), such as intra-data center (DC) links or data center interconnect (DCI) systems. This is true for previous generations of DCI systems where there is no flexible tuning of modulation formats and also where transmission performance (e.g. signal to noise ratio, SNR) is not dominated by optical fibers. However, for next and future generations of DCI systems, probabilistic constellation shaping (PCS) technology is very likely to be used which provides fine-granuality tuning of modulation formats, meaning that optical signal to noise ratio (OSNR) improvements due to low fiber loss will directly translate into higher data capacity. Thus, low fiber loss (e.g. attenuation rate less than 0.17 dB/km, more preferably less than 0.16 dB/km) leads to about 8% to about 35% data capacity increase for data center links over 50 km, as compared to systems with attenuation rate of 0.2 dB/km optical fiber. Moreover, per wavelength data capacity approaches saturation in next generation DCI systems, which leads to constraints of optical transceiver implementation penalties. Low fiber loss will increase link OSNR and relax transceiver implementation constraints.
Embodiments of the optical fiber disclosed herein having low fiber dispersion (e.g. absolute value less than 10 ps/nm/km, more preferably less than 5 ps/nm/km) reduces or removes the complexity of digital chromatic dispersion (CD) compensation. Furthermore, embodiments of the optical fiber disclosed herein provides power consumption of 0.5 W to 4.5 W depending on fiber length and dispersion coefficient, as compared to standard single mode fiber, which is a substantial improvement considering that the entire optical transceiver power consumption is around 15 W to 20 W.
Fiber dispersion slope and effective area have little impact on data capacity and CD compensation complexity. Therefore, the benefits of the proposed optical fiber disclosed herein will not be diminished even if practical fabrication leads to moderately higher dispersion slope and smaller effective area as compared with standard single mode fiber.
Lower fiber loss shows SNR improvement at low launch power region. Smaller dispersion and smaller effective area result in higher nonlinear distortions, especially at high launch power regions. However, comparing the different effective areas of fiber D, very little difference in SNR is shown at low launch power region up to −2 dBm. Practical DCI systems operate at low launch power region to avoid nonlinear distortions and to reduce power consumption. Therefore, no significant SNR penalty will occur even if the proposed low loss low dispersion fiber has a smaller effective area than standard single mode fiber
It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the illustrated embodiments. Since modifications, combinations, sub-combinations and variations of the disclosed embodiments that incorporate the spirit and substance of the illustrated embodiments may occur to persons skilled in the art, the description should be construed to include everything within the scope of the appended claims and their equivalents.
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/969,395 filed on Feb. 3, 2020, the content of which is relied upon and incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62969395 | Feb 2020 | US |
