Quantum-noise randomized data encryption for wavelength-division-multiplexed fiber-optic networks

We demonstrate high-rate randomized data-encryption through optical fibers using the inherent quantum-measurement noise of coherent states of light. Specifically, we demonstrate $650\mathrm{Mbit}∕\mathrm{s}$ data encryption through a $10\mathrm{Gbit}∕\mathrm{s}$ data-bearing, in-line amplified 200-km-long line. In our protocol, legitimate users (who share a short secret key) communicate using an $M$-ry signal set while an attacker (who does not share the secret key) is forced to contend with the fundamental and irreducible quantum-measurement noise of coherent states. Implementations of our protocol using both polarization-encoded signal sets as well as polarization-insensitive phase-keyed signal sets are experimentally and theoretically evaluated. Different from the performance criteria for the cryptographic objective of key generation (quantum key-generation), one possible set of performance criteria for the cryptographic objective of data encryption is established and carefully considered.

Figure 1

Top: $M$ pairs of orthogonal polarization states uniformly span a great circle of the Poincaré sphere; bottom: $M$ pairs of antipodal phase states uniformly span a phase circle.

Figure 2

Summary of the quantum-noise protected data-encryption protocol. In our experiments, the “pseudorandom key extender” is implemented by a maximal-length LFSR and an “$r$-bit-to-$r$-bit mapping function.”

Figure 3

Shannon information recovered through individual attacks on the message when launching either the optimal positive operator-valued measure or an ideal heterodyne measurement on the time-mode (left) and polarization-mode (right) implementations. Plotted as a function of ${\mid \alpha \mid }^2$, for several values of $M$.

Figure 4

Left, transmitter/receiver setup: G1, RF power amplifier; OA1, low-noise EDFA followed by a Bragg-grating filter; G2, RF signal amplifier. Right, WDM network setup: OA1, low-noise EDFA; G3, IM driver; OA2, in-line EDFA followed by an optical isolator; OA3, EDFA.

Figure 5

(a) Optical spectrum (left) and eye pattern (right) of a PRBS channel at launch [after AWG2 in Fig. 4 (right)]. (b) Optical spectrum (left) and eye pattern (right) of a PRBS channel at the end of the line [before AWG3 in Fig. 4 (right)].

Figure 6

Five-kbit segments of 9.1-Mbit transmissions through the WDM link. Insets, the received bitmap images. Top, Bob’s detection; bottom, Eve’s detection.

Figure 7

Left: Transmitter-receiver setup. G1, RF power amplifier; OA2, low-noise EDFA followed by a 25-GHz-passband Bragg-grating filter; PMF, polarization-maintaining fiber; Circ., optical circulator. Right: 200-km in-line amplified line. IM, $10\mathrm{Gbit}∕\mathrm{s}$ intensity modulator; DCM, dispersion-compensation module; RCVR, $10\mathrm{Gbit}∕\mathrm{s}$ In-Ga-As $p\text{−}i\text{−}n$ TIA optical receiver; G2, $10\mathrm{Gbit}∕\mathrm{s}$ modulator driver.

Figure 8

(a) Optical spectrum (left) and eye pattern of a PRBS channel (right) at launch [after AWG2 in Fig. 7 (right)]. (b) Optical spectrum (left) and eye pattern of a PRBS channel (right) after in-line amplification [before AWG3 in Fig. 7 (right)].

Figure 9

Top: Eye pattern and histogram of Bob’s decrypted signal after 200 km propagation in the WDM line. Bottom: Eye pattern and histogram of Eve’s measurements at the transmitter. Insets, received 1 Mb bitmap file transmissions.