Ge APD Research Articles

Experimental results for optimum coded digital PPM with Ge APD receiver and Gaussian noise approximated theory

Practical and theory results are presented for an optical (λ = 1.523 μm) digital PPM system using a suboptimum filtered Ge APD receiver. These original results show that an optimum coding level and APD gain exists for received FWHM Gaussian pulse widths of 11.3 and 35 ns. These optima compare well with those predicted by a suboptimum filter, APD model using Gaussian approximated noise statistics.

Influence of the various types of noise on jitter performance in binary direct detection optical communications

Nowadays, people are using very high transmission bit rates (multigigabit per second) to exploit the full bandwidth of single-mode fibre in direct detection optical fibre communications. Hence, it is convenient to develop efficient analytical tools to compute the jitter arising in multigigabit systems. These analytical tools may be generalised to the study of jitter inherent in laser transmitters. A general analytical method based on the moment generating function (MGF) was developed to compute and optimise the jitter performance in optical fibre regenerators. It is capable of dealing with any type of prefilter, nonlinearity, linear narrow band-pass filter, photo-detector device, optical pulse shape, output filter pulse shape and line-code. In this paper, we analyse the influence of circuit, quantum signal and dark current noises on jitter performance in binary direct detection optical receivers. It is seen that, in terms of jitter performance and with low signal to noise ratio, an APD, with quantum signal noise dominance, presents the best choice; a PIN, in which the circuit noise is dominant, is the next preferred choice and a Ge APD, with the dark current noise dominance, is the worst choice. The results obtained with application of this method allow the development of design rules for the optical receivers.

Monolithic integrated CMI coder and decoder for gigabit optical links

The high-speed performance of a monolithic integrated CMI coder and decoder, which are fabricated using super self-aligned process technology, is described. The maximum line rate is 3.07 Gbaud. The power consumptions of the coder and decoder are 0.54 W and 0 43 W, respectively. An optical CMI transmission experiment was performed using an InGaAsP/InP laser diode, a Ge APD and an integrated receiver with a SAW filter retiming circuit. When the quality factor Q was 830 at 1.8 Gbaud, random jitter was below 0.7°. In addition, it was confirmed that a clock signal can be extracted from any input data.

2 Gbit/s and 2.4 Gbit/s optical transmission field trial over a 32 km installed route

High-speed optical data transmission at 2Gbit/s and 2.4 Gbit/s has been demonstrated for the first time over an installed fibre-optic cable. Error-free transmission with operating margins of 15.8 dB and 12 dB over 10?9 BER was achieved over a 32 km route. The systems featured a 1.5 ?m DFB laser, Ge APD transimpedance receivers and full regeneration.

Long-span optical transmission experiment over 222.8 km of commercial monomode fibre at 140 Mbit/s and 1.525 μm

A 140 Mbit/s optical transmission experiment has been conducted over 222.8 km of commercially available monomode, step-index fibre using a 1.525 μm ridge-waveguide DFB laser and hybrid Ge APD receiver. An overall system margin of 1.2 dB was observed after full regeneration.

Germanium reachthrough avalanche photodiodes for optical communication systems at 1.55-µm wavelength region

Germanium reachthrough avalanche photodiodes (Ge RAPD's) with high-frequency response have been designed, fabricated, and tested. In the calculation of frequency response, optimum depletion layer width of 21 µm has been found for 1.55-µm wavelength with the highest cutoff frequency of 830 MHz. The diodes fabricated by this design showed frequency degradation of less than 2 dB at 500 MHz and at 1.55 µm. This response has been unchanged up to 1.58 µm, indicating useful spectral limit lies at more than 1.58 µm. The diodes exhibited quantum efficiency of 80 percent and excess noise factor of 6.1 at a multiplication of 10 both for 1.55 µm. The breakdown voltage was 60- 90 v. The sensitivity of the diodes was measured at 100 Mb/s and 1.55 µm. The minimum detectable power of -44.3 dBm which is by 5.2 dB better than the conventional p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -n Ge APD has been achieved for 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-11</sup> error rate. Comparison with InGaAs APD and p-i-n/FET receiver has been made by calculating minimum detectable power of RAPD at 500 Mb/s. Calculated sensitivity of RAPD is 1-2 dB worse than InGaAS APD and comparable to that of InGaAs p-i-n/FET receiver estimated from the reported experimental results.

A 100-km-long single-mode optical-fiber fault location

A Raman OTDR (ROTDR) fault location for a 100-km-long single-mode optical fiber has been tested. A Ge p-i-n photodiode cooled by liquid nitrogen has been used as a backscattered light receiver. The signal-to-noise ration (SNR) improvement of the cooled Ge p-i-n photodiode from a Ge avalanche photodiode (Ge APD), which operates at room temperature, is 14 dB. Spectral Stokes light power distributions, which have been emitted from a long single-mode fiber, have been measured to estimate the maximum locatable length for a single-mode fiber. It has been shown, from the measurements and calculations, that a 100- km-long and a 30-dB total attenuation at a 1.55-μm wavelength single-mode fiber fault location can be achieved with the aid of an averaging technique. On the basis of these results, a 102-km-long single-mode fiber fault location experiment has been successfully carried out.

High-sensitivity Hi-Lo germanium avalanche photodiode for 1.5 μm-wavelength optical communication

A high-sensitivity small-detectable-area Hi-Lo germanium avalanche photodiode (Ge APD) was developed for use in 1.55 μm wavelength optical communication systems. This device has Hi-Lo (p + nn - ) impurity profile. Its detectable area is 30 μm in diameter for single-mode optical-fibre use. The minimum average received signal level obtained was -40.5 dBm (at 450 Mbit/s, λ = 1.55 μm, BER = 10 -9 , return-to-zero). This is 0.7 dB better than the value for the 80μm diameter similar structure Ge APD.

Long-wavelength transimpedance optical receiver performance enhancement using cooled germanium avalanche photodiodes

An optical sensitivity improvement of 1.5 dB was produced by moderate cooling of a commercially available 100 μm p+-n Ge APD in a transimpedance receiver, built on a standard printed circuit board. At 1.3 μm and 140 Mbaud, −45.2 dBm was achieved, making this receiver highly competitive where cooling is permitted.

Novel optical FSK heterodyne single filter detection system using a directly modulated DFB-laser diode

A novel optical FSK heterodyne single filter detection system, which can use direct modulation and can tolerate the relatively large spectral width of a laser diode, is proposed. The receiver sensitivity improvement, as much as 8 dB over direct detection using a Ge APD, has been achieved after 105 km transmission at 100 Mbit/s.

Receiver sensitivity temperature dependence of small detectable area Hi-Lo germanium avalanche photodiode

Optical receiver sensitivity temperature dependence is measured in different detectable area (80, 30 μm-diameter) Hi-Lo Ge APD modules at 450 Mbit/s bit rates. A 30 μm-diameter device has a little power penalty against temperature increase compared with an 80 μm-diameter device, with 2.4 dB receiver sensitivity improvement at 45°C.

1.8 Gbit/s 65 km optical transmission experiment using a 1.478 μm DFB laser and Ge APD receiver

A 1.8 Gbit/s optical transmission system trial has been conducted over 65 km of conventional monomode fibre using a 1.478 μm DFB laser and p + n Ge APD receiver. Using a 2 15 -1, NRZ, PRB test sequence, a long-term BER of 2×10 -10 was achieved. Dispersive effects introduced a 1 dB penalty after 65 km transmission.

565 Mbaud 100 km optical system trial using a ridge waveguide DFB laser at 1.478 μm

565 Mbaud transmission over 100 km of step-index mono-mode fibre using a new ridge waveguide distributed feedback (DFB) laser structure operating at 1.478 μm and a Ge APD receiver has been demonstrated. No residual dispersion penalty was observed.

An optical time-domain reflectometer with low-power InGaAsP diode laser

An optical time-domain reflectometer (OTDR) suited for operation with low-power (of the order of 1-mW peak power) InGaAsP lasers is described. To launch maximum average power into the fiber, the laser is modulated by a pseudonoise binary sequence, and the back-scattered signal is averaged and then analyzed by a microcomputer. Initial tests of the reflectometer with a germanium avalanche photodiode (Ge APD) detector demonstrate backscattering signal levels at 1300 nm from 50-μm core diameter graded-index fibers of more than 15 dB above the system noise.

Reliability of Light Emitters and Detectors for Optical Fiber Communication Systems

Life test results on light emitters and detectors showed promisingly long lifetimes for short and long wavelength optical fiber communication systems. Data are presented on 0.85 μm AIGaAs LD's and LED's, Si APD's and p-i-n-PD's, 1.3 μm InGaAsP LD's and LED's, and Ge APD's and PD's. Degradation mechanisms and counteractions are also discussed.

Noise and responsivity of commercial p+n Ge avalanche photodiodes

Commercial p+n Ge APD samples from two manufacturers are shown to have comparable noise and responsivity, characterised by a quantum efficiency at 1.3 μm wavelength of 0.7–0.75, and a bulk leakage current density at 20 C of 2−3×10−4 A cm−2 before avalanche multiplication. Surface uniformity of avalanche gain is much better than on earlier n+p devices of the same diameter (100 μm).

Gigabit/s optical receiver sensitivity and zero-dispersion single-mode fiber transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 μm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p+nn- Ge APD. The p+nn- Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55μm and a 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> error rate, which was 4 dB better than the receiving level with a p+n Ge APD. Detector performance at 1.3μm was also studied for comparison with performance at 1.55μm. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55μm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) . km at 1.55μm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3μm dispersion-free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.

Gigabit/s Optical Receiver Sensitivity and Zero-Dispersion Single-Mode Fiber Transmission at 1.55 µm

High-speed pulse response and receiver sensitivity at 1.55 µm were measured at data rates ranging from 400 Mbits/s to 2 Gbits/s, in order to elucidate characteristics of a reach-through p/sup +/nn/sup -/ Ge APD. The p/sup +/nn/sup -/ Ge APD receiver provided a 2 Gbit/s received optical power level of -32.0 dBm at 1.55 µm and a 10/sup -9/ error rate, which was 4 dB better than the receiving level with a p/sup +/n Ge APD. Detector performance at 1.3 µm was also studied for comparison with performance at 1.55 um. Single-mode fibers, which have 0.54 dB/km loss and zero dispersion at 1.55 µm, and an optical transmitter-receiver, whose repeater gain is 29.2 dB, have enabled 51.5 km fiber transmission at 2 Gbits/s. The transmission system used in this study has a data rate repeater-spacing product of 103 (Gbits/s) /spl dot/ km at 1.55 µm. Optical pulse broadening and fiber dispersion were also studied, using 1.55 and 1.3 µm dispersion free fibers. Future repeater spacing prospects for PCM-IM single-mode fiber transmission systems are discussed based on these experimental results.

Characteristics of Gbit/s Optical Receiver Sensitivity and Long-Span Single-Mode Fiber Transmission at 1.3 &amp;#181;m

Sensitivity of a 1.3 µm Ge APD receiver was measured at data rates ranging from 100 Mbits/s to 2 Gbits/s, using a high-speed GaAs FET RZ driver, low-noise Si bipolar transistor (BIT) receiver amplifier,, a highly sensitive TD comparator. The required received optical level at a 10/sup -9/ error rate was -31.9 dBm for 2 Gbits/s with a Ge APD/Si BIT front end having a 50 Omega input impedance. A Ge APD/ GaAs FET front end, with a 500 Omega input impedance, brought about 2 dB improvement at 100 Mbits/s, as compared with a Ge APD/Si BIT (50 Omega) front end. A coupling loss of 4 dB, achieved by a hemispherical microlens tipped on a single-mode fiber, and a low fiber loss of 0.57 dB/km, including splice loss, enabled 44.3 km single-mode fiber transmission at 2 Gbits/s. The 1.3 µm transmission system has a data rate repeater-spacing product of 88.6 (Gbit/s)km. Prospects of Gbit/s receiver sensitivity, the 2 Gbit/s transmission system, with more than 50 km repeater spacing, are also discussed.

Characteristics of Gbit/s optical receiver sensitivity and long-span single-mode fiber transmission at 1.3 µm

Sensitivity of a 1.3 μm Ge APD receiver was measured at data rates ranging from 100 Mbits/s to 2 Gbits/s, using a high-speed GaAs FET RZ driver, low-noise Si bipolar transistor (BIT) receiver amplifier, and a highly sensitive TD comparator. The required received optical level at a 10-9error rate was -31.9 dBm for 2 Gbits/s with a Ge APD/Si BIT front end having a 50 Ω input impedance. A Ge APD/ GaAs FET front end, with a 500 Ω input impedance, brought about 2 dB improvement at 100 Mbits/s, as compared with a Ge APD/Si BIT (50 Ω) front end. A coupling loss of 4 dB, achieved by a hemispherical microlens tipped on a single-mode fiber, and a low fiber loss of 0.57 dB/km, including splice loss, enabled 44.3 km single-mode fiber transmission at 2 Gbits/s. The 1.3 μm transmission system has a data rate repeater-spacing product of 88.6 (Gbit/s)km. Prospects of Gbit/s receiver sensitivity and the 2 Gbit/s transmission system, with more than 50 km repeater spacing, are also discussed.