Conference Publication Details
Mandatory Fields
Huynh T.;Nguyen L.;Barry L.
IEEE Photonic Society 24th Annual Meeting, PHO 2011
Coherent optical receiver using phase modulation detection
2011
December
Published
1
()
Optional Fields
771
772
We propose a coherent receiver scheme based on phase modulation (PM) detection that recovers the in-phase (I) and quadrature (Q) components of the optical signal and potentially simplifies the front-end of a coherent optical receiver [1]. The scheme has been demonstrated for a differentially coherent, self-heterodyne receiver via simulations for DQPSK and experimentally for DBPSK. Fig. 1 shows the experimental setup in which the upper arm of the interferometer has a one-symbol delay and the lower arm is phase modulated by a sine wave. The incident E-field on the photo-detector can be written as E 1(t)=0.5[E(t-T s)-E(t)xe j[bsin(ωct+φc)]], where E(t)=√Pa(t)e jφ(t)e eωot is received optical E-field with optical frequency ω o and power P. φ(t) and T s respectively are the symbol phase modulation and duration (at 2 GSps symbol rate), a(t) is the normalized symbol amplitude modulation. For brevity we have omitted the laser phase and intensity noises. The input signal to the phase modulator is bsin(ω ct + φ c) where b is the PM index, ω c and φ c are the angular frequency and phase of the modulating carrier at 2 GHz, respectively. The output current of the photo-detector with responsivity R is proportional to the intensity of the incident field: i (t) = R x E i(t)E* i(t)= 0.25RP{a 2 (t) a 2(t-T s) -2a(t)a(t-T s)cos[ω oT s+φ(t)-φ(t-T s)b sin(ω ct+φ c)]} Ignoring the first two terms (which can be cancelled using balanced photo-detectors) and expanding the third term: i(t) = -0.5RPa(t)a(t-T s)cos[ω oT s + φ(t)-φ(t-T s)+b sin(ω ct+φ c)] equations Using the Bessel coefficient expansions: equations where J k(b) is the Bessel function of the first kind with integer order k, we find that the I and Q components of the complex differential optical modulation envelope, a(t)a(t-T s)e j[φ(t)-φ(t-Ts)], can be found at the even and odd harmonics of i(t). In particular, we have at the first and second harmonics: Q(t)∼2J 1(b)a(t)a(t-T s)sin[φ(t)-φ(t-T s) + ω oT s]sin(ω ct + φ c) I(t)∼-2J 2(b)a(t)a(t-T s)cos[φ(t)-φ(t-T s) + ω oT s]cos[2(ω ct + φ c)] and at base-band: I(t)∼-J o(b)a(t)a(t-T s)cos[φ(t)-φ(t-T s) + ω oT s] © 2011 IEEE.
10.1109/PHO.2011.6110778
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