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The Deterministic MPDC Source essentially runs multiple probabilistic SPDC photon sources in parallel (multiplexing) to create a deterministic output. The system pulses all photon sources simultaneously to probabilistically generate entangled pairs. When a desired four-photon emission occurs at one of the banked sources, two of these photons are directed into a polarization analyzer equipped with photon detectors. If the heralding signal successfully confirms multiple photons, the analyzer verifies that the correct two-photon N00N state has been created on the heralded pair state pathway. If fewer than two photons are detected, the system discards the emissions, effectively filtering out vacuum noise and unwanted multipair states. This automated filtering prevents noise from falsely triggering adjacent nodes in a communication chain. The successful heralding signal then triggers a controller connected to an optical switch yard. When a correct signal is detected, the switch yard turns "on" the corresponding source's pathway, routing the heralded pair into a single output mode for network injection. Delay lines are seamlessly incorporated into each source's pathway to allow the optical switches enough time to act. Ultimately, this architecture achieves a highly deterministic operating regime with an estimated 86% probability that at least one source generates a valid herald event during each pulse. The Deterministic MPDC source is available for patent licensing.

The core of the technology is the SAW division de-multiplexing method (LEW-19920-1). It uses a commercially available double-clad fiber optic cable with a 9um core and a 105um first cladding. By optimizing the wavelengths of the QKD photon and data transmission, a single focusing lens can create a diffraction pattern that directs the QKD photons to the 9um core and the data signal to the 105um secondary core. Key components of the system include: • SOA Driver With Wideband Current Control (LEW-19913-1): This device allows a semiconductor optical amplifier (SOA) or laser to be driven with an arbitrary current at a rate of over 100 MHz. This enables the rapid generation of sub-nanosecond laser pulses with one of four polarization states, which is necessary for QKD. • Random Bit Generator with Linear Feedback Shift Register LFSR Scrambler (LEW-20058-1): This device produces random bits by combining the output of a noise source with a pseudorandom bitstream from the LFSR. This allows a random basis set to be generated on demand for a polarization modulator. • Variable-length quantum key conversion (LEW-20224-1): Since QKD operations produce keys of varying lengths, a strategy was developed to "digest" these raw keys using a hash function, such as SHAKE256. This process generates a fixed-length output that is useful for symmetric encryption schemes like AES256. • The system also incorporates a Discretization Algorithm for Numerical Wave Optics Simulations (LEW-20119-1), which can accurately model the effects of atmospheric turbulence on the propagating optical beam.