In this paper a very low power optical communications system is addressed that could be developed specifically for creating networks involving a planetary lander and fixed or mobile sensor stations that could be as small as 1 cm3. The communication system is a variant of photon-counting based communications. Instead of counting individual photons, the system only counts the arrival of time coincident sets of photons. Using sets of photons significantly decreases the bit error rate because they are highly identifiable in the presence of ambient light.An experiment demonstrating reliable communication over a distance of 70 m using less than a billionth of a watt of radiated power is presented. The experiment also compares this technique to traditional photon counting and successfully demonstrates that time coincident photon communications can achieve an equivalent bit error rate at a signal-to-noise ratio that is 5 to 7 dB lower than what is needed for classical photon counting communication. The components used in this system were chosen so that they could in the future be integrated into a cubic centimeter device.
In this paper a very low power optical communications system is addressed that could be developed specifically for creating networks involving a planetary lander and fixed or mobile sensor stations that could be as small as 1 cm3. The communication system is a variant of photon-counting based communications. Instead of counting individual photons, the system only counts the arrival of time coincident sets of photons. Using sets of photons significantly decreases the bit error rate because they are highly identifiable in the presence of ambient light.An experiment demonstrating reliable communication over a distance of 70 m using less than a billionth of a watt of radiated power is presented. The experiment also compares this technique to traditional photon counting and successfully demonstrates that time coincident photon communications can achieve an equivalent bit error rate at a signal-to-noise ratio that is 5 to 7 dB lower than what is needed for classical photon counting communication. The components used in this system were chosen so that they could in the future be integrated into a cubic centimeter device.
One concept for planetary exploration involves using many small robotic landers that can cover more ground than a single conventional lander. In addressing this vision, NASA has been challenged in the National Nanotechnology Initiative to research the development of miniature robots built from nano-sized components. These robots have very significant challenges, such as mobility and communication, given the small size and limited power generation capability. The research presented here has been focused on developing a communications system that has the potential for providing ultra-low power communications for robots such as these. In this paper an optical communications technique that is based on transmitting recognizable sets of photons is presented. Previously pairs of photons that have an entangled quantum state have been shown to be recognizable in ambient light. The main drawback to utilizing entangled photons is that they can only be generated through a very energy inefficient nonlinear process. In this paper a new technique that generates sets of photons from pulsed sources is described and an experimental system demonstrating this technique is presented. This technique of generating photon sets from pulsed sources has the distinct advantage in that it is much more flexible and energy efficient, and is well suited to take advantage of the very high energy efficiencies that are possible when using nano scale sources. For these reasons the communication system presented in this paper is well suited for use in very small, low power landers and rovers. In this paper a very low power optical communications system for miniature robots, as small as 1 cu cm is addressed. The communication system is a variant of photon counting communications. Instead of counting individual photons the system only counts the arrival of time coincident sets of photons. Using sets of photons significantly decreases the bit error rate because they are highly identifiable in the presence of ambient light. An experiment demonstrating reliable communication over a distance of 70 meters using less than a billionth of a watt of radiated power is presented. The components used in this system were chosen so that they could in the future be integrated into a cubic centimeter device.
One way to improve the acquisi tion of planetary information from robotic landers is to use many smaller robotic explorers that can cover more ground than a single conventional rover , given that the existing launch capabilities constrain the mass of planetary robotic landers to a relati vely fixed value . In addressing this vision, NASA has been challenged in the National Nanotechnology Initiative to research the development of miniature robots built from nano -sized components. These robots have very significant challenges, such as mobil ity and communication, given the small size and limited power generation capability. The research presented here has been focused on developing a communications system that has the potential for provid ing ultra -low power communications for robots such as t hese. In this paper an optical communications technique that is based on quantum entangled photons is presented. This technique both minimizes radiated power and is appropriate for the size scale of the robot. Simulations of this system show that the rad iated power may be reduced to extremely low levels for line -of -sight communication over distances of several kilometers, even in the presence of ambient light. The immunity to background noise makes this technique very promising in comparison to classical optical communications for ultra -low power applications. The results of t his research will generate requirements definitions for transceiver components built from nanotechnology. Results from experiments demonstrating aspects of this communications techn ique are presented.
Quantum communications and quantum cryptography are developing rapidly during the last decades caused partly by a fast progress in quantum computing. Quantum cryptography provides an unconditionally secure way of communicating whereas traditional classical cryptographic protocols are likely to be broken by super powerful quantum computers. In the past few years distances covered by quantum communications have increased by an order of magnitude. To provide a global coverage for the quantum networks, a satellite based quantum communications is the most promising solution. \n \nAs an emerging field, QKD systems are still under evolution process. Despite outstanding security proven theoretically, it has loopholes caused by their implementations. To test QKD, find the possible loopholes and suggest ways to fix them, is a job of many scientific groups. \nIn this thesis I start with presenting my work for a securing test of a commercial QKD system Clavis2. A Trojan-horse attack on Bob's apparatus was prepared by testing reflections and transmissions of all optical components in Bob's scheme. The attack was implemented and found to be unsuccessful at the tested wavelengths due to afterpulsing effect in Bob's single-photon detectors reacting to the bright light attack pulses. \n \nThree chapters of the thesis are dedicated to custom built single-photon detectors (SPDs) based on commercial Silicon avalanche photodiodes (APDs). Those detectors demonstrate parameters that altogether are not possible to find in commercially available SPDs, especially if combined with a very compact size. One of the in-lab-built SPDs was implemented in 143 km teleportation experiment, where a low dark count rate was crucial for the success of the experiment. The next generation SPD is already built, characterized and ready to be implemented. \n \nAnother 4-channel SPD was built as a prototype for a quantum satellite SPD. It has light weight, low electrical power consumption, low dark count rate and decent other parameters. It was used in the airborne demonstration of QKD receiver payload experiment, when a secret key was successfully generated between a moving aircraft and a ground station. \n \nSPDs installed on a satellite have to be able to work in the harsh space environment during a mission life time. Space radiation dramatically increases dark count rate of APDs. The last project presented in the thesis committed to a radiation test of three types of APDs and one type of photo multiplier tube. The experiment included characterization of all SPDs before and after irradiation by four levels of proton radiation, equivalent to 3 months - 2 years duration in a 600 km low Earth orbit. Three methods for mitigating radiation damage were tested and found to be successful with perspective to use some of them on a quantum satellite to extent life time of SPDs. \n \nTo summarize, this work makes a contribution to the development of SPDs for global quantum communications.
The development of modern technology extends human presence beyond cislunar space and onto other planets, which presents an urgent need for high-capacity, long-distance and interplanetary communication. Communication using photons as carriers has a high channel capacity, but the optical diffraction limit in deep space leads to inevitable huge geometric loss, setting an insurmountable transmission distance for existing optical communication technologies. Here, we propose and experimentally demonstrate a photon-inter-correlation optical communication (PICOC) against an ultra-high channel loss. We treat light as a stream of photons, and retrieve the additional information of internal correlation and photon statistics globally from extremely weak pulse sequences. We successfully manage to build high-fidelity communication channel with a loss up to 160dB by separating a single-photon signal embedded in a noise ten times higher. With only commercially available telescopes, PICOC allows establishment of communication links from Mars to Earth communication using a milliwatt laser, and from the edge of the solar system to Earth using a few watts laser.
Because noise is inherent to all measurements, optical communication requires error identification and correction to protect and recover user data. Yet, error correction, routinely used in classical receivers, has not been applied to receivers that take advantage of quantum measurement. Here, we show how information uniquely available in a quantum measurement can be employed for efficient error correction. Our quantum-enabled forward error correction protocol operates on quadrature phase shift keying (QPSK) and achieves more than 80 dB error suppression compared to the raw symbol error rate and approximately 40 dB improvement of symbol error rates beyond the QPSK classical limit. With a symbol error rate below 10−9 for just 11 photons per bit, this approach enables reliable use of quantum receivers for ultra-low power optical communications. Limiting optical power improves the information capacity of optical links and enables scalable networks with coexisting quantum and classical channels in the same optical fiber.
Single photon per bit optical communication between ground stations and low earth orbit satellites will enable the secure global distribution of cryptographic keys. The communications satellite AO-40 contains an experimental infra-red payload consisting of a low power 835 nm laser diode transmitter coupled to a small fixed orientation telescope transmitting 400 baud Manchester encoded data [1]. The received signal levels are of the order of 10 photons/bit for an effective telescope aperture of diameter 100 mm [2]. They therefore offer a means of validating models of low photon number OOK signal propagation and detection in the presence of atmospheric turbulence, an issue relevant to free-space quantum communications. This paper describes the design, testing and implementation of a photon counting receiver for AO-40 signals using a Labview software platform to display received data, error statistics, detection and correction (using cyclic redundancy check code CRCC 32), and clock synchronization [3]. Signals are acquired with a 300 mm f/6.3 Schmidt-Cassegrain tracking telescope coupled by 100 micron multimode fibre to a silicon APD photon counting module. References 1. R. Purvinskis, Use of the fixed orientation optical transmitter on AO-40, Internal Report, Centre for Advanced Telecommunications and Quantum Electronics, University of Canberra, 2001. 2. A. Arora, Oscar 40: A Complete Link Analysis, University of Canberra BE (Hons) Report, November 2001. 3. A. Arora, Optical Modulator and Demodulator for the Oscar-40 Satellite, University of Canberra BE Project Report , November 2001.