Photonic Generation of Phase Coded Microwave Pulses Using Cascaded Polarization Modulators

Abstract

We demonstrate a technique of generating a binary phase coded microwave pulse based on two cascaded polarization modulators (PolMs). The first PolM (PolM1) followed by an optical band-pass filter is used to generate two phase-locked and polarization orthogonal optical frequencies. The second PolM (PolM2) aims to change their polarization states. A polarizer attached to the output of PolM2 allows only one of the two optical frequencies passing, or combines them with positive/negative phase difference. By changing the voltage level of the electrical modulation signal applied to PolM2, a series of binary phase coded microwave pulses is directly generated from a continuous wave microwave signal in the optical domain. In the proposed system, the precise amplitude control or amplification of the modulation signal are avoided. The waveform of the generated pulse is very stable. For a proof-of-concept experiment, a series of 25-GHz pulses with ∼2.08-ns pulse duration and ∼10.24-ns repetition time is generated. The pulses are phase coded by a 13-bit Barker code.

Generation of a Frequency-Quadrupled Phase-Coded Signal With Large Tunability

“…To overcome this problem, polarization modulation based approaches were proposed [7][8][9][10][11][12], in which two orthogonally-polarized wavelengths are first generated and then complementarily phase modulated in a polarization modulator (PolM). One of the key steps in these approaches is the generation of the orthogonally-polarized wavelength pair, which can be realized by employing a differential group delay (DGD) element [7], a polarization-maintaining FBG (PM-FBG) [8], a PolM followed by an optical filter (OF) [9][10][11], or a dual-parallel polarization modulator [12]. However, all these approaches can only generate a phase-coded signal in a relatively small frequency range which is limited by the frequency dependence of the optical components or the bandwidth of the modulators and electrical devices.…”

Simultaneous photonic generation of two microwave signals with precisely-controllable phase difference using orthogonal polarization modes

“…Photonic microwave or millimeter-wave generation based on optical beat notes has been studied extensively [1,2,3,4] with the development of ultra-high speed photodetectors in recent years [5,6]. These photonic generation schemes are attractive because they enable high-frequency selectivity over the entire RF region as well as high-speed phase control via electro-optic phase modulators such as traveling-wave type lithium niobate (LN) phase modulators, which are widely used in optical communication systems [7,8].…”

Photonic generation of phase-modulated microwave signals

“…The limitation associated with this method is that the generated microwave signal is hardly reconfigurable. On the other hand, optical heterodyning has been proposed to generate phase-modulated microwave signal [5][6][7]. By heterodyning two optical carriers in the PD, the microwave signal with a frequency corresponding to the frequency interval of the two optical carriers is generated.…”