An MZM uses an applied electric field to vary the refractive index of the waveguide carrying a light beam. This in turn modulates the phase, amplitude, or polarization of the light and can achieve direct optical upconverstion of the modulating electronic signal into an Optical Single Side Band (OSSB) signal in the output beam for radio over fiber communications. MZMs can be dual drive (each beam is split into two, separately modulated then recombined) or single drive.
Mach-Zehnder modulator (MZM)
Phase-match(ed)
When power is transferred between modes, links, wave guides, etc., maximum efficiency is achieved when the phase differences between the incident wave and propagating wave are zero over the temperature and frequency ranges of operation. RFOptic devices have small phase differences under operating conditions.
Chromatic Dispersion
Chromatic dispersion arises from the variation in propagation velocity with wavelength. Over distance (time), an initially sharp pulse is broadened and begins to overlap with adjacent pulses causing degraded signal quality, limiting transmission distances and capacities of long-haul fiber links.
The higher the data rate (e.g., 40 Gbit/s or 160 Gbit/s) the stronger the pulse broadening relative to lower rates (e.g., 10 Gbit/s, for example).
Dispersion compensator
The most common solution to chromatic dispersion is ‘dispersion compensating fiber’ (DCF). This is a length of fiber in which the chromatic dispersion has been engineered to be the exact opposite of the dispersion in the fiber link. For more information regarding specific solutions on this, refer to this link: https://www.sciencedirect.com/topics/materials-science/dispersion-compensating-fiber.
EDFA Optical Amplification
Erbium-doped Fiber Amplification
Erbium-doped fiber amplifiers are a type of optical repeater/regenerator used to periodically boost optical signal power along the long-haul fiber length.
Working Principle
The erbium fiber is illuminated by 980 nm or 1480 nm light. This pushes the erbium into a quasi-stable intermediate state. From here, it can decay to its ground state spontaneously or – incoming light can cause it to decay by stimulated emission and simultaneous amplification of the light.
Advantages
– EDFA has high pump power utilization (>50%)
– Directly and simultaneously amplify a wide wavelength band (>80nm) in the
C-Band region (1530 – 1570nm) , with relatively flat gain.
– Flatness can be improved by gain-flattening optical filters.
– Gain in excess of 50 dB
– Low noise figure suitable for long haul applications
Drone (UAV)
Drone-UAV RF Communication
RFOptic’s Drone and UAV RFoF Remote Antenna enables bi-directional RFoF support between an RF antenna used to communicate with a UAV and its controller in cases where the two are separated by varying distances and are connected via optical fiber (which does not emit RF radiation).
The uplink control signals to the antenna are sent over single-mode, optical fiber; the downlink data from the UAV are converted to RFoF and are sent over the same fiber.
This enables placing significant distance between the RF antenna that is in physical communication with a drone and the drone operator or control vehicle. Although the antenna can be targeted, the distant operator is not.
The system delivers the full 4GHz – 6GHz band commonly used by such UAV controllers, and can be customized to support other frequency ranges up to 12GHz and 18GHz
Doppler
The Doppler effect is the difference between the frequency at which waves leave a source and that at which they reach an observer.
Although optical signals can be propagated over distances with limited power loss, the purity (frequency, phase) of the signals can be degraded during propagation due to thermal, mechanical, and electrical perturbations affecting the optical length of the fiber.
The spurious level of RFOptic’s Optical Delay Line is small and supports Doppler shift measurements / applications where the noises caused due to the circuit boards are cleaned by the system.
Optical switching speed
Optical switching is a method to change fiber length in progressive ODLs. The standard switching time is approximately 10 ms however special techniques can shorten this time to 100 µs and less.
Full Duplex and Half Duplex
In half-duplex transmission a channel is used for two-way transmission but only one direction can be used at a time.
Full duplex transmission enables simultaneous transmission in both directions.
0.5MHz — 2.5 GHz for GPS
Modules support 0.15GHz – 2.5GHz for GPS and GNSS.
Bias-T with regulated 5V and 200mA (max) feed on the RF In port powers active GPS antenna.
Load resistor on the RF Out port draws current from the GPS antenna to bypass failsafe GPS receivers.
Noise Figure: 6 dB with LNA; -169 dB/Hz MDS
Impedance: 50 Ohm / 75 Ohm
The RFoF link has excellent gain flatness with ±0.5dB gain tracking between links.
Temperature stable operation supports 0.5 dB over 100° C range.
Module power: 5VDC —12VDC.
Remote management using GUI on PC.
SW Adjustable: Noise Figure, link gain, Input P1dB, and IP3 on
Tx / Rx modules using LNA’s variable attenuators.
SW activated LNA supports RF input power below -100dBm/1MHz and 5dB Noise Figure for low signal applications.
Configurations:
- Bias-T for GPS applications
- Outdoor enclosure (unidirectional/bi-directional)
- 1U Generic enclosure (4 units)
- (1,2,3)U Removable panel enclosure (4/8/12) units
0.5MHz — 2.5 GHz RFoF Module
Modules support up to 2.5GHz.
RFOptic’s RF over Fiber (RFoF) modules are suitable for telecommunications, satellite, radio telescopes, distribution antennas, audio and video broadcasting, and timing synchronization.
Tx modules convert the RF to RFoF optical signal; Rx modules reconvert the RFoF optical signal back to RF. Tx/Rx units are connected by a single-mode fiber.
The Tx and Rx LNAs and variable attenuators enable customers to adjust the Noise Figure, Input P1dB, and IP3 over wide dynamic ranges. LNA can be operated using RFoF software enabling RF input power of -100 dBm/1MHz for wideband applications, low Noise Figure of 6 dB. Gain flatness between links with 0.5dB gain tracking. Temperature stable operation supports 0.5 dB over 100° C .
Module power: 5VDC —12VDC.
Local and remote SW adjustment of the RF and optical parameters including link gain, Noise Figure, P1dB, Optical power, LED indication and module information.
Configurations:
- Outdoor enclosure (unidirectional/bi-directional)
- 1U Generic enclosure (4 units)
- (1,2,3)U Removable panel enclosure (4/8/12) units
0.5MHz — 3.0 GHz RFoF Module
Modules support 0.5GHz – 3.0GHz
RFOptic’s RF over Fiber (RFoF) modules are suitable for telecommunications, satellite, radio telescopes, distribution antennas, audio and video broadcasting, and timing synchronization.
Tx modules convert the RF to RFoF optical signal; Rx modules reconvert the RFoF optical signal back to RF. Tx/Rx units are connected by a single-mode fiber.
The Tx and Rx LNAs and variable attenuators enable customers to adjust the Noise Figure, Input P1dB, and IP3 over wide dynamic ranges. LNA can be operated using RFoF software enabling RF input power of -100 dBm/1MHz for wideband applications, low Noise Figure of 6 dB. Gain flatness between links with 0.5dB gain tracking. Temperature stable operation supports 0.5 dB over 100° C .
Module power: 5VDC —12VDC.
Local and remote SW adjustment of the RF and optical parameters including link gain, Noise Figure, P1dB, Optical power, LED indication and module information.
Configurations:
- Standalone RFoF Tx/Rx units
- Unidirectional/Bidirectional configurations
- 19” 1U Generic enclosure (up to 8 RFoF units)
- 19” 1U Removable enclosure (up to 4 RFoF units)
- 19” 2U Removable enclosure (up to 8 RFoF units)
- 19” HD enclosure (up to 40 RFoF unidirectional units or
20 Bidirectional terminals) - Mini RFoF enclosure (up to 2 RFoF units)
- Small outdoor enclosure (up to 6 RFoF units)
- Large outdoor enclosure (up to 8 RFoF units)
0.5MHz — 4.0GHz RFoF Module
Modules support 0.5GHz – 4.0 GHz.
RFOptic’s RF over Fiber (RFoF) modules are suitable for telecommunications, satellite, radio telescopes, distribution antennas, audio and video broadcasting, and timing synchronization.
Tx modules convert the RF to RFoF optical signal; Rx modules reconvert the RFoF optical signal back to RF. Tx/Rx units are connected by single-mode fiber.
The Tx and Rx LNAs and variable attenuators enable customers to adjust parameters such as the Noise Figure, Input P1dB, and IP3 over wide dynamic ranges. LNA can be operated using RFoF software enabling RF input power of -100 dBm/1MHz for wideband applications, low Noise Figure of 6 dB. Gain flatness between links with 0.5dB gain tracking. Temperature stable operation supports 0.5 dB over 100° C .
Module power: 5VDC —12VDC.
Local and remote SW adjustment of the RF and optical parameters including link gain, Noise Figure, P1dB, optical power, LED indication and module information.
Configurations:
- Standalone RFoF Tx/Rx units
- Unidirectional/Bidirectional configurations
- 19” 1U Generic enclosure (up to 8 RFoF units)
- 19” 1U Removable enclosure (up to 4 RFoF units)
- 19” 2U Removable enclosure (up to 8 RFoF units)
- 19” HD enclosure (up to 40 RFoF units
20 Bidirectional terminals) - Mini RFoF enclosure (up to 2 RFoF units)
- Small outdoor enclosure (up to 4 RFoF units)
- Large outdoor enclosure (up to 8 RFoF units)
0.5MHz — 6.0 GHz RFoF Module
Modules support 0.5GHz – 6.0GHz.
RFOptic’s RF over Fiber (RFoF) modules are suitable for telecommunications, satellite, radio telescopes, distribution antennas, audio and video broadcasting, and timing synchronization.
Tx modules convert the RF to RFoF optical signal; Rx modules reconvert the RFoF optical signal back to RF. Tx/Rx units are connected by a single-mode fiber.
The Tx and Rx LNAs and variable attenuators enable customers to adjust the Noise Figure, Input P1dB, and IP3 over wide dynamic ranges. LNA can be operated using RFoF software enabling RF input power of -100 dBm/1MHz for wideband applications, low Noise Figure of 6 dB. Gain flatness between links with 0.5dB gain tracking. Temperature stable operation supports 0.5 dB over 100° C .
Module power: 5VDC —12VDC.
Local and remote SW adjustment of the RF and optical parameters including link gain, Noise Figure, P1dB, Optical power, LED indication and module information.
Configurations:
- Standalone RFoF Tx/Rx units
- Unidirectional/Bidirectional configurations
- 19” 1U Generic enclosure (up to 8 RFoF units)
- 19” 1U Removable enclosure (up to 4 RFoF units)
- 19” 2U Removable enclosure (up to 8 RFoF units)
- 19” HD enclosure (up to 40 RFoF units
20 Bidirectional terminals) - Mini RFoF enclosure (up to 2 RFoF units)
- Small outdoor enclosure (up to 4 RFoF units)
- Large outdoor enclosure (up to 8 RFoF units)”
5G
Fifth generation cell phone technologies are the latest generation of cellular technologies currently being deployed by carriers around the world. 5G enables faster data transfer than earlier generations, better responsiveness (lower latency), and the ability to simultaneously connect more devices ( sensors and smart devices).
5G deployment began in 2019.
5G challenges / RFOptic testing solutions
RFOptic offers several end-to-end solutions for 5G testing, which address the challenges of complex routing, distances, and wide bandwidth that are needed for 5G deployments. The 5G testing solutions reduce OPEX dramatically by providing software configurable RFoF terminals.
All monitoring and configuration are done via RFOptic’s HTML Monitor & Control system typically, using the REST protocol.
Optical RF measuring and testing solutions
Testing solutions include an Optical Delay Line and RADAR Altimeter Test, radiation testing, and cable replacement due to EMC challenges using optical RF.
The RADAR Altimeter Test provides a high-performance solution for testing and calibrating RADAR Altimeter systems. It enables users to replicate the landing and taking off with real-time accuracy for pilot training. This customized Optical Delay Line solution with high-resolution delay steps “tricks” a flight simulator’s altimeter into thinking it is flying, including taking off and landing scenarios.
The radiation testing solution enables radiation testing on airplanes. Our optical RF measuring solution enables test engineers to perform these tests using a compact portable link and a chargeable battery.
Attenuation - Optical Fiber Attenuation - 880
“Attenuation is the reduction in (optical) signal strength between two points in the system. It is defined as the ratio of the powers at those two points. For optical fiber, the power being compared are the input power and the output power and is expressed as the logarithm of that ratio in decibels (dB).
For optical fiber it is common to normalize the attenuation by the fiber length. This attenuation coefficient is expressed in dB/unit length, typically kilometers (km).
Power loss as function of attenuation:
Attenuation . Loss
10.0 dB ……………… 90%
3.0 dB ……………… 50%
0.1 dB ………………. 2%”
Fiber Attenuation Coefficient - 30
The rate of optical power loss with respect to fiber length, usually measured in decibels per kilometer (dB/km at a specific wavelength. Lower numbers mean less loss. In optical fibers, typical single-mode wavelengths are 1310 and 1550 nm; typical multimode wavelengths are 850 and 1300 nanometers (nm).
Bi-directional configurations
RFOptic’s RFoF (RF over Fiber) transceiver is comprised of a 2-way (bidirectional) Tx and Rx uplink (at 1550nm) and a Tx and Rx downlink (at 1310nm).
The transceiver employs WDM technology to use a single fiber link.
The transceivers support 0.05 – 2.5GHz, 3GHz, 4GHz, and 6GHz.
The RFoF software enables adjustment of the RF and Optical
parameters, such as: link gain, noise figure, P1dB, optical power, LED indication and module information (locally or remotely).
In addition, the RFoF link has full diagnostic capability, including Tx, Rx and complete link test (optical and RF).
For applications that require temperature stable operation, a unique algorithm supporting 0.5 dB over -200C to +70C may be activated.
The RFoF links operate on DC power from 5 – 12 volts.
Fiber Optic Cable Assembly
Optical fiber cable with connectors installed on one or both ends. Cable assemblies are used to connect optical fiber to optical and opto-electronic equipment.
Pigtails describes fiber with connectors attached to only one end of a cable.
Jumper or patch cord describes fiber with connectors attached to both ends of a cable.
Optical Cladding
The dielectric material surrounding the optical fiber core. It generally has a lower index of refraction than the core.
Coaxial/Coax Cable
Coaxial cables serve as electrical transmission lines that carry high radio frequency (RF) signals from one point to another. Losses depend, in part, on the exact frequencies carried.
Parts of the coax cable are:
- The center or core conductor (of specific diameter) that carries the rf signal.
- A dielectric insulator of specific thickness that surrounds the core.
- A braided, metallic, electromagnetic shield surrounding the insulator and cancels EM noise.
- A Jacket (wrapper) that surrounds the above.
Coherent fiber light
Light in which the phase relationship between points in the beam is constant.
Core (optical cable)
The central part of an optical fiber. Optical signals propagate through the core.
Coupling loss
The power loss (usually in dB) that occurs when light is transferred from one optical component to another.
DAS
A Distributed Antenna System (DAS) enables cellular coverage to areas where outdoor 5G cell tower signals cannot reach.
Decibel
A decibel expresses a relative change in power or root-power values or change relative to a reference value. It was originally used to measure transmission and power losses in telephone systems.
For power levels (energy or sound density) a decibel is defined as:
the (base10) logarithmic ratio of the values of two power levels.
dB = 10log (P2/P1)
10 dB refers to values that are 10X stronger than 0 dB.
20 dB refers to values that are 100X stronger than 0 dB.
When measuring root-power values (voltages, currents, field strengths) the definition is:
dB = 20log(V2/V1); or
dB = 20log(I2/I1)
Regarding sound:
0 dB is the smallest human-audible sound.
Note: Power is proportional the square of current, voltage, etc.).
Detection
Recovery of the original modulating signal from the carrier.
Dielectric
An electrical insulator comprised of a substance in which an electric field can be maintained with zero power consumption.
Distortion Wave
A change in the shape of the signal waveform during transmission through the fiber.
Duplex cable
An optical cable composed of two fibers.
Fiber amplifier
A device that amplifies an optical signal directly, without first converting it back to an electrical signal.
Frequency shifting
RFOptic frequency shifting uses the incoming RF signal to modulate
an LED beam. The modulated beam contains all the information of the RF signal. It can then be transmitted over fiber optic cable. See Radio-over-fiber.
FWHM (Full Width Half Maximum)
The Full Width at Half Maximum (FWHM) parameter describes the width of a spectral peak
on a curve or function. It is given by the distance between points on the curve where the function reaches half its maximum amplitude.
FMCW Radar
Frequency Modulated Continuous Wave Radar
FMCWR broadcasts a repeating frequency modulated signal. The broadcast signal reflects from the moving object and is mixed with the original at the detector. The signals at time T1 are compared to determine Δf (the frequency shift); this gives the D1 (the target’s distance). The signals are compared again at time T2 to give D2. Speed is determined by comparing the calculated distances and times.
Angle to the target can be determined using spatially separated antennas to determine the direction of arrival of the signals.
Range, azimuth, elevation direction, and velocity can be calculated using additional processing techniques.
GPSoF
A GPS-over-fiber optical link (GPSoF) extends the antenna feeder cable length well beyond the maximum distance supported by coaxial cable-based systems.
IP-54
Standard for water penetration to outdoor enclosure.
M&C (Monitoring and Control)
RF Monitor and Control software manages, monitors, and controls RF over Fiber converters and RFoF systems locally or remotely.
M&C: HTML and Ethernet and ethernet protocols
RFOptic’s Optical RF Monitor & Control uses a USB interface for local management; it uses SNMP V2c, HTML webserver and REST protocol for remote management.
Both systems enable changing operating parameters and provide status details for all RFOptic’s RFoF products.
An Inter-Facility Link (IFL) feature enables monitoring and control of the remote cage over the same fiber bundle that connects the remote and local sites.
An RFOptic ODL panel-level control enables using an LCD and a 3-button navigation pad to control the system without a computer.
mmWave
mmWaves for 5G use in the USA are currently defined by the FCC as the frequency range from 24GHz – 47GHz. Eventually the FCC will license the 57-64GHz range (currently unused) and the slightly used 71GHZ, 81GHz and 92GHz ranges.
These high frequencies support fast data transmission but necessarily, individual links have short ranges.
Note: Formally, millimeter frequencies of millimeter waves are 30GHz – 300GHz.
Optical Modes
An electromagnetic field distribution that satisfies Maxwell’s equations and the boundary conditions of the waveguide (e.g., optical fiber).
Modes (laser modes)
Laser modes refer to the standing waves that can be generated in the cavity of the laser generating the light beam.
Multimode fiber
Optical fibers that support more than one TEM mode.
RFOptic devices support single mode fibers.
Multimode fiber
Optical fibers that support more than one TEM mode.
RFOptic devices support single mode fibers.
ODL (optical delay line)
An optical delay line (ODL) is an electric-optic-electric instrument that provides fixed time delay of RF signals. RF signal frequencies can be as low as 0.1 GHz up to 20 GHz and higher; delay times can be as short as a few nanoseconds up to several hundred microseconds.
ODL (optical delay line)
An optical delay line (ODL) is an electric-optic-electric instrument that provides fixed time delay of RF signals. RF signal frequencies can be as low as 0.1 GHz up to 20 GHz and higher; delay times can be as short as a few nanoseconds up to several hundred microseconds.
Optical link
An optical transmission channel that may include repeaters or regenerative repeaters for connecting two communication terminals.
Note: Can include the terminal optical transmitter and receiver.
Optical receiver
An apparatus that receives an optical signal, detects it, and processes it as required.
Optical repeater
An apparatus that amplifies an optical input signal to extend the link distance.
Optical-electrical-optical (OEO) devices can correct distortion of the optical signal by converting it to an electrical signal, processing it (reshaping and/or retiming), then retransmitting the processed signal as an optical signal.
Optical-only devices use non-linear optical fibers, frequency shifting and frequency generation to regenerate the signal.
Optical transceiver
An apparatus that combines the functions of an optical transmitter and an optical receiver.
Photodiode
A solid-state diode in which electric current is produced or enhanced by the absorption of light.
Silicon photodiodes: Silicon-based PN or PIN-junction photodiodes used for direct detection of optical wavelengths shorter than approximately 1 um.
Germanium photodiodes must be used for wavelengths longer than approximately 1 um.
Radio over fiber
In RFoF an optical beam is modulated by an RF signal and transmitted over fiber optic cable. Optical signals have lower transmission losses, less distortion and less electromagnetic interference. In addition, multiple types of RF signals can be carried over a single fiber optic cable to a central location
Single-mode fiber
Single mode fiber optic cable has a small diameter (~9 microns in diameter) light conducting core that enables only one mode of light to pass through. The result is a narrower beam of light, lower transmission losses, and longer transmission distances than multimode fibers.
TEM Mode (Transverse Electromagnetic Mode)
The light used for optical communication is generated such that the shape of its amplitude is described by the product of a Hermite polynomial and a Gaussian function. The solution to these equations gives the TEMm,n modes.
These modes are electromagnetic waves whose electric and magnetic fields are perpendicular to each other and perpendicular to the direction of travel. The wavefront is uniform, symmetrical has no electric or magnetic field components along the direction of propagation.
In TEMm,n → “m” refers to the vertical direction, “n” refers to the horizontal direction. When both m and n = 0, the beam is Gaussian. It is the fundamental mode with the best beam quality.
Very Long Baseline Interferometry (VLBI)
VLBI is a technique based on multiple radio astronomy telescopes on Earth, at which the signals from very distant astronomical radio sources, such as quasars, are collected simultaneously and processed.