Ultralow noise pre-amplified receiver for free-space optical communications
Doktorsavhandling, 2020

The demand for high data rate in space communication links is increasing due to the growth of space exploration missions inter-satellite, and satellite-to-Earth data transmission. Optical communication systems capable of handling hundreds of Gigabits per second data transmission with a single light carrier and are suitable for such space links. In addition, light offers smaller beam divergence in space due to the shorter wavelength compared to radio frequency beams (RF), resulting in smaller link loss and smaller size receiver apertures required.

The receiver sensitivity is one of the key factors that determines the capacity and reach for such long haul communication links. Currently, there is a search for the optimal modulation format and receiver implementation combination to achieve the best sensitivity for error-free transmission. In this thesis, we discuss and implement the best possible

combination of these, both theoretically and experimentally. Phase sensitive parametric optical amplifier (PSA) can amplify optical signals ideally without adding any excess noise, limited only by quantum fluctuations. Employing these as preamplifiers in free-space receivers can thus improve the sensitivity compared to erbium doped fiber amplifiers. We implement a two-mode PSA with a noise figure of 1.2 dB, which can amplify both quadratures of a signal, being used as a pre-amplifier in coherent receiver setup. We experimentally demonstrate a record black-box sensitivity of 1 photon-per-bit using PSA receiver for quadrature phase shift keying (QPSK) modulation format at 10.5 Gbps with 100 % overhead forward error correction code. This sensitivity also includes ultra-low pump power (-72 dBm) which is recovered using pre-amplified injection locking. We also investigate the most power efficient modulation formats, where a combination of m-(pulse-position modulation) PPM+QPSK with higher m-values provides best sensitivity at relatively high received SNR-per-bit, while QPSK outperforms all formats investigated at very low SNR-per-bit, which is ideal for space communications.


noise figure

optical injection locking

Phase sensitive amplifier

Kollektorn, Kemivagen 9
Opponent: Prof. Andrew Ellis, Aston University, UK


Ravikiran Kakarla

Chalmers, Mikroteknologi och nanovetenskap, Fotonik

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The presentation was held at Universium, Göteborg on the topic ‘Space communication using light’.

It was about why space optical communications has been introduced over radio wave space communications. To satisfy the future demands of the space exploration and human expeditions, we need ultra-high-speed data transmission. The main reasons being increased space activities such as study of planetary surfaces, exploration of life in other planets and search for life sustaining planets.  One of the audiences commented on this ‘I liked the part where the future if optical communications decides how live on other planets’.

In my research project, I implement ‘phase sensitive optical amplifiers’ for high-sensitive communications which can improve the sensitivity significantly compared to traditional communication systems. This is assumed to be implemented in space receivers for improved sensitivity. As this sounds little technical, one of the audiences commented on this ‘‘I would ask him to be little more basic and understandable to everyone’.

It is already demonstrated that, using laser light, one can transmit and receive at giga bits per second rates from moon to earth.  A practical demonstration of the communication between mars and earth, is going to takes place in 2021 by NASA also to other planets in the coming decade. This is reflected some feedbacks with comments such as ‘Best part is the last slide showing satellite to satellite communication earth to mars’ and ‘I enjoyed the presentation, it has lots of pictures and animations. Best part is mars to earth communication’.

There was a question about, ‘how an image on mars converted to light and transmitted’, which is where I had to explain about optical modulation and demodulation, which is a part of our research.


Informations- och kommunikationsteknik


Atom- och molekylfysik och optik

Annan fysik

Elektroteknik och elektronik

Annan elektroteknik och elektronik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4812



Kollektorn, Kemivagen 9


Opponent: Prof. Andrew Ellis, Aston University, UK

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