Patent Application
20230393354
The present invention generally relates to the field of high-speed optical fiber communication channels and, more specifically, to a low latency optical channel. The disclosed apparatus and method enables optical communication signals to propagate through free-space, thereby traveling at the speed of light in air minimizing propagation time. The disclosed apparatus and method provide low latency optical signal paths for a multiplicity of discrete channels equalizing the propagation delay between adjacent channels.
Free-space optical communications (in various forms), has been used for thousands of years. The ancient Greeks used a coded alphabetic system of signals to communicate utilizing torches. In 1880, Alexander Graham Bell created the photophone, which he considered his most important invention and was the world's first wireless telephone. Bell demonstrated voice communications over free-space optics between two buildings some 213 meters apart. During the trench warfare of World War I, red filtered light signals provided undetected communications at night. Currently, free-space optical communications are widely used in commercial, military, and space applications.
Today, large data centers utilize optical fiber communications to achieve the high-speed and long channel reaches required for the switch-to-switch and switch-to-server interconnections. In the field of high-speed trading in financial markets, traders demand minimum transaction delay and guaranteed equivalent optical signal delay compared to other traders. Presently, these high-speed transactions propagate over standard single-mode and/or multimode optical fibers. To guarantee equivalent trading delays, optical fiber cable assemblies are custom manufactured where the discrete fiber lengths within said cable are precisely measured using optical time domain refractometers (OTDRs) to ensure the optical channel delays are equivalent.
To reduce the propagation delay of the optical channel, fiber manufacturers are developing hollow core fibers, where the core is a channel of air surrounded by an array of hollow tubes which form reflective micro-structures cladding, to confine the optical beam,
Hence, there is a need for a low-cost solution where, the optical signal propagates near that of the speed of light in vacuum so that channels of said communication signals undergo minimum delay, and traders can be guaranteed equivalent optical channel paths.
The speed of an optical signal is determined by the refractive index of the medium in which it propagates, where the refractive index is effectively the optical dielectric constant of the medium. The refractive index, n, is defined by,
where, c is the speed of light in vacuum (299,792,458 m/s), and v is the speed of the optical signal in the medium. In general, the refractive index of glass, as used in optical fibers is about 1.467. Hence, the speed of light in optical fiber is 204,357,504 m/s, or 68% of the maxiinum speed of light in vacuum. Given a typical channel length of 75 m, the time of flight in vacuum is 250 ns. For light propagating through glass optical fiber, the time of flight for a 75 m channel is 367 ns, introducing a delay of 117 ns, or 0.117 μs. For high-speed trading, this is not acceptable.
The authors of this disclosure measured the refractive index, and hence the optical signal delay in a commercially available hollow core fiber (hcf). The refractive index was found to be nhcf=1.000476, yielding a 0.0476% delay compared to vacuum.
In
In the present invention, we disclose apparatus and method for free space optical communication channels to be used in high-speed trading applications, where the channels do not have to utilize expensive hollow core fibers.
A low latency free-space optical data communication channel has at least one optical collimator for transmitting an optical communication signal in the form of a parallel beam across a free-space channel. The input of the collimator includes a connectorized optical fiber pigtail for connecting said collimator to a glass optical fiber carrying the signal to be transmitted across the free-space channel. The optical beam propagates in free space along the longitudinal axis of a raceway, which is at least partially enclosed. The second optical collimator located at the distant end of said raceway, is positioned to receive the free-space optical communication signal. The received signal is focused into a second optical fiber pigtail at the output side of the collimator, thereby resulting in a pigtailed free-space low latency optical channel link.
Free-space optical communications requires two necessary conditions: line-of-sight, and an unobstructed optical path, i.e., channel. In
To protect and enclose the low latency free-space optical channel for communication applications according to the present invention, the collimated light path is enclosed within a channel raceway commonly used to carry fiber optic cables,
In order to optically align the transmit and receive collimators located on the opposing raceway end caps, a kinematic mirror cell (i.e., mount) 500 is attached to each end cap 504,
In the preferred embodiment, end cap 504 is fitted with one or more optical adapters. In
The free-space light path can be extended by adding one or more raceway subsections using a raceway coupler 304, as shown in
The concatenation of two free-space communication raceway channel links, will allow a change in physical direction if required, however, a change in direction will not be the shortest optical path between two points e.g., switch and server, and consequently, the low latency objective will be violated. It is important to note that since hollow core fiber cables are flexible, and require slack when installed, the optical path length will be longer than the free-space channel of the present invention. The disclosed method enables a true point-to-point, line-of-sight optical channel providing the shortest channel delay for light propagating through air. The speed of light in air is 299,702,547 m/s, 89,911 m/s slower than vacuum, and has a refractive index of 1.000300. Comparing the disclosed method to hollow core fiber where, nhcf=1.000476, we get a 0.02% reduction in delay.
Hollow core fibers are designed for single-mode laser transmitters, typically utilizing distributed feedback lasers (DFB). DFB lasers are significantly more expensive than their multimode vertical cavity surface emitting laser (VCSEL) counterpart. It is therefore, advantageous to use multimode collimators for low cost VCSEL based transceivers as described in this disclosed invention.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.
CROSS-REFERENCE TO RELATED APPLICATION(S) This application claims benefit to U.S. Provisional Patent Application Ser. No. 62/818,912, filed on Mar. 15, 2019, the entirety of which is hereby incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 63349750 | Jun 2022 | US |
