What is meant by Highly Integrated Photonics?

HIP is integration of multiple photonic components on a single chip for ruggedization, smaller packaged modules, and cost reduction. This enables a single photonic module to perform the same functions as multiple, discrete fiber components.

What problems are solved with photonics?

As interconnect speeds get faster (reaching the tens of GHz or Gbps range), electrons traveling in copper cables face increasing loss and consequently require additional amplification, which results in increased power consumption and heat generation. Optical communication over fiber is much more efficient and scalable to higher signal bandwidths with minimal transmission losses. Optical fiber cables also have zero susceptibility and emission of electromagnetic radiation.

What is so special about APIC’s processes?

APIC has designed extremely low noise lasers and high dynamic range photodetector optical receivers for use in demanding environments. These devices are fabricated to exacting standards to obtain the required performance.

Are Photonics in use today?

Fiber optic photonic links are used by all the major telecommunications companies and an extensive supplier base has developed. Fiber links and networks are also being implemented on aerospace platforms to meet new and projected bandwidth requirements.

What is RF over Fiber (RFoF)?

RFoF is the transmission of radio frequency signals (analog or digital) at through optical fiber. Optical transmitters modulate the coherent light from the laser with the RF signal which is then transmitted through fiber cables. At the receiving end a photodetector converts the light energy back into an electronic RF signal.

What applications use RFoF?

RFoF is used to consolidate and replace multiple electrical cables in systems with more compact fiber optic cables to take advantage of fiber’s higher bandwidth, EMI resistance, and ease of installation and maintenance. Application examples include:

  • High speed signal transmission applications over 18 GHz and/or transmission lengths greater than 20 feet where copper cable losses are significant
  • Passive optical networks (PON) such as for high bandwidth cable TV/Internet
  • Distributed antenna systems (DAS), where high bandwidth fiber optics is used to preserve and re-use valuable RF spectrum

What is “high fidelity” RF over Fiber?

“High Fidelity” RF over fiber retains the highest quality signal transmission through fiber optics. It requires very low noise laser sources; a large dynamic range in the link; and highly linear response of the active components.

How is “high fidelity” achieved in an RFoF link?

High fidelity links require optimization of a number of parameters in the link and link components:

  • Eliminating/suppressing sources of noise, including optical and electrical elements
  • Highly linear devices which do not distort the signal
  • Operation of the link at high optical power which lowers noise floor and increases dynamic range to enable operation around the most linear point in the link response curve
  • High responsivity detectors to improve link gain and dynamic range

What are the key requirements for the laser in a high fidelity link?

The laser in the RFoF link requires the following:

  • Low relative intensity noise (RIN); RIN < 160 dB/Hz2/3
  • High optical power; > 50 mW
  • Single mode operation with good side-mode suppression ratio (SMSR > 35 dB) under operating conditions
  • Low threshold current

What is a direct modulated transmitter?

The laser emits an RF modulated optical signal. A directly modulated transmitter varies the drive current of the laser according to the RF input signal, which causes the optical signal intensity to be modulated by the input signal (i.e. amplitude modulation).

What is the advantage of a direct modulated transmitter versus an external modulator?

The advantages of direct modulation are:

  • Significantly lower cost
  • Better dynamic range of the link
  • Significantly smaller form factor; eliminates space needed for external modulator and modulator control electronics

What are the characteristics of a high fidelity photo detector?

  • Capable of operating at high input power (at least 50 mW for 20 GHz, preferably higher)
  • High maximum linear photocurrent (> 50 mA)
  • High Responsivity > 0.8 for 20 GHz RF bandwidth

How does copper compare with multi mode fiber, and with single mode fiber used by APIC?

Copper Coax Cable Multi-Mode Fiber Single-Mode Fiber
Size and Weight Large diameter, stiff, and higher weight Flexible, Lightweight
Power Requirements Higher due to signal loss Low
Cable RF Signal Loss per 100 ft 10 dB at 1 GHz
30 dB at 10 GHz
0.03 dB, independent of frequency 0.01 dB, independent of frequency
Bandwidth Limited High Even Higher
Scalability No—requires additional cables Yes—Multiple fibers with little impact on cable size Yes—Multiple fibers or WDM in single fiber
Wavelength Division Multiplexing No Coarse WDM Coarse or Dense WDM
EMI Susceptibility and Emission from Cable High unless heavily shielded None
Corrosion Susceptibility Yes No