Burst-mode receiver

A burst-mode receiver (BMR) is an optical receiver designed to handle a time-division-multiplexed signal in which sequential bursts arrive from different optical transmitters, with each burst potentially having different amplitude, phase, and arrival time. This contrasts with a continuous-mode receiver, which receives a single steady signal of approximately constant amplitude.

Standard application: passive optical networks (PON). In a typical fiber-to-the-home PON architecture:

• A central optical line terminal (OLT) at the central office serves up to 64 or 128 optical network units (ONUs) at customer premises
• Downstream traffic (OLT → ONUs) is broadcast: all ONUs see all data; each ONU keeps only data addressed to it
• Upstream traffic (ONUs → OLT) is TDMA: each ONU transmits during its scheduled time slot
• The OLT receiver sees the upstream signal as a sequence of bursts, one per scheduled ONU

The bursts vary in optical power by typically 5 – 15 dB depending on the distance to each ONU and the optical losses along its specific path. Each burst arrives with arbitrary phase relative to the previous one (each ONU has its own free-running clock).

Key challenges and design responses.

Wide dynamic range. A continuous-mode receiver can be designed with adjustable gain or a tightly-controlled input power; a burst-mode receiver must accept the widest input power range without saturation or below-noise-floor operation. Standard approach: AC-coupled amplifier with very fast settling time, or DC-coupled with automatic gain control (AGC) that re-acquires within a few bits of each new burst.

Fast clock recovery. A continuous-mode receiver uses a phase-locked loop (PLL) with long lock acquisition time (kHz – MHz bandwidth); a burst-mode receiver must recover clock and lock within a few bit periods of burst arrival. Standard approach: oversampled clock and data recovery (e.g., $3 - 5\times$ oversampling) with phase detector that can lock within $\sim 8 - 32$ bits.

Burst preamble. Each transmitted burst begins with a known synchronization pattern — the preamble — that the receiver uses to:

• Detect that a burst has arrived (energy detection)
• Recover the receiver's gain setting and DC offset for this burst
• Lock the clock recovery to the bit-rate
• Confirm bit-phase alignment

Typical preamble length: 50 – 200 bits at the line rate. The PON MAC layer specifies preamble structure for vendor interoperability.

PON-specific standards.

Standard	Date rate (upstream)	Wavelength (upstream)	Typical BMR sensitivity
GPON	1.25 Gbps	1310 nm	$-28$ dBm
XG-PON	2.5 Gbps	1310 nm	$-29$ dBm
XGS-PON	10 Gbps	1270 nm	$-28$ dBm
NG-PON2	10 Gbps	wavelength-tunable	$-30$ dBm
25G-PON	25 Gbps	1320 nm	$-25$ dBm
50G-PON	50 Gbps	1300 nm	$-22$ dBm
100G-PON	100 Gbps (initial deployments 2026+)	TBD	TBD

The sensitivity is typically 3 – 5 dB worse than for an equivalent continuous-mode receiver, due to:

• DC offset uncertainty contributing to decision-threshold error
• Faster AGC time constants reducing time-averaged sensitivity
• Burst-mode specific noise contributions

Implementation technologies.

• TIA + LA + CDR (transimpedance amplifier + limiting amplifier + clock-data recovery): the standard analog receiver architecture, with burst-mode adaptations
• DC-coupled BMR: explicit AGC with feedback control of the TIA gain at burst level; better sensitivity but higher complexity
• AC-coupled BMR: capacitive coupling with high-pass filtering; simpler but lower sensitivity at low bit rates
• Digital-burst-mode receiver: high-speed ADC followed by all-digital processing; highest performance but highest power

Optical components. The burst-mode receiver photodiode is typically an avalanche photodiode (APD) to achieve the necessary sensitivity at the link budget. PON OLTs use:

• InGaAs APD for receiver
• 1490 nm or 1577 nm DFB for downstream transmitter
• Wavelength-division multiplexer to combine TX and RX wavelengths on the same fiber

Comparison to coherent reception. Some next-generation PON systems (NG-PON2, future 100G-PON) consider coherent reception, which would replace direct-detection burst-mode receivers with coherent burst-mode receivers. The DSP-based coherent BMR can in principle reduce per-burst preamble length (because coherent reception is more sensitive and recovers faster) but increases the per-port cost significantly.

References: ITU-T G.984 series (GPON), G.987 series (XG-PON), G.9807 (XGS-PON); Effenberger et al., XG-PON: A Status Update, IEEE Communications Magazine 2011.