JP2861178B2 - Time division optical separation circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a time division optical separation circuit used in an optical communication system.

(Prior Art) In recent years, research has been conducted on an optical fiber transmission system having a transmission speed of 10 Gb / s class for the purpose of improving the performance of the optical fiber transmission system and large-capacity communication. Such large-capacity optical communication systems include an optical transmission system and an optical reception system that respond at high speed, a time-division multiplexing circuit (MUX) that generates large-capacity data by time-division multiplexing, and small-capacity data from large-capacity data. It is essential to develop a time division separation circuit (DMUX) that separates data into data. In the development of such MUX and DMUX, high-speed logic operation is being realized by high-speed Si-IC or GaAs-IC. Examples of DMUX using such high-speed ICs include:
“Submicron Silicon Bipolar Master- by K.RUNGE and others
Slave D-Type Flip-Flop for use as 8.1Gb / s decision
Circuits and 11.2Gb / s Demulti plexer "(Electronic
s Letters' 1989 vol.25). In this example
A DMUX that separates 11 Gb / s electric signals into two 5.5 Gb / s electric signals using Si-IC is realized.

However, since the response speed of the MUX and DMUX using such an IC is limited by the speed of the transistor cell of the IC, it is becoming difficult to perform a higher-speed logic operation. In addition, in the DMUX using such an IC, the circuit is complicated, so that the production yield of the circuit is poor.

Therefore, in order to realize a high-speed optical data time-division circuit, a method of directly performing time-division multiplexing and time-division separation on an optical data signal by using an optical switch as light is being attempted. For example, “Multi-Gbitls Opti by LCBlank
cal time division multiplexing employing LiNbO ₃ sw
itches with low-frequency sinewave drive. "(Electr
onics Letters, 1989, vol. 24). In this example, time division multiplexing and time division demultiplexing of an optical signal are performed using an optical switch using a directional coupler type LiNbO ₃ ,
MUX and DMUX operation at 12Gb / s is realized. This MUX, DMUX
Then, the electrode of the directional coupler type LiNbO ₃ optical switch is provided with N times (speed B · N) or 1 / N of the data transmission speed B of the optical signal.
By applying a clock signal voltage twice (speed B / N), data multiplexing (MUX) of optical signals or data separation (DMUX) of optical signals is realized.

(Problems to be Solved by the Invention) However, in the device for directly MUX and DMUX of the optical data signal described above, since a directional coupler type optical switch of LiNbO ₃ is used, the shape of the optical switch is large and it is difficult to implement the device. In addition, the LiNbO ₃ optical switch has a disadvantage that the drive voltage is high at present and there is a problem such as drift, so that the reliability of the device is low.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a time-division optical separation circuit for optical data signals using a semiconductor optical modulator capable of downsizing circuits and devices.

(Means for Solving the Problems) A first time-division light separating circuit according to the present invention comprises a semiconductor optical modulator that changes a light absorption rate when a voltage is applied and converts absorbed light into a current; A light detector that is optically coupled to the optical modulator and converts received light into a current, and a time-division multiplexed optical signal is input to the semiconductor optical modulator; 1 / N of data transmission rate (N is 2
Or a positive integer greater than that), a clock signal voltage is applied, the light transmitted through the semiconductor optical modulator is input to the photodetector, and the light signal is output from the semiconductor optical modulator from the optical signal. A bit signal synchronized with the clock signal voltage is extracted as a current, and the remaining signal of the optical signal is extracted as a current from the photodetector.

Further, the second time-division light separating circuit according to the present invention is such that when a voltage optically cascaded to an input optical signal is applied, the light absorptance changes and the absorbed light is converted into a current. Semiconductor optical modulators, wherein the optical signal is an optical signal having a transmission rate of B in which N data signals are time-division multiplexed, and the N semiconductor optical modulators have a rate of B / N. Clock signal voltages are applied with a phase difference of 2π / N, respectively.
Each of the optical signals from the N semiconductor optical modulators is 1 /
It is characterized in that a data signal time-division-divided into N is extracted as a current.

(Operation) The time-division light separation circuit of the present invention uses a semiconductor optical modulator that changes the light absorption rate by applying a voltage and converts the absorbed light into a current as a time-division light separation element. The time-division multiplexed optical signal is absorbed in the semiconductor optical modulator at 1 / N bit intervals, and the optical signals with other bit intervals pass through the semiconductor optical modulator without loss.

The operating principle of the semiconductor optical modulator used in the time division light splitting circuit of the present invention will be described with reference to FIG.

FIG. 3 is a diagram for explaining a time-division demultiplexing operation in a case where a two-series time-division multiplexed optical signal is time-division-demultiplexed at a half bit interval using a semiconductor optical modulator. FIG. 3 (a) shows a waveform of an optical signal having a transmission rate B input to the semiconductor optical modulator. This optical waveform is a waveform obtained by time-division multiplexing of two series of data signals. FIG. 3B shows a waveform of a clock signal voltage at a speed B / 2 input to the semiconductor optical modulator.

In the semiconductor optical modulator of the present invention, when a clock signal voltage is applied and an optical signal is input at the same time, the optical signal is absorbed in the semiconductor optical modulator and converted into a current. On the other hand, when no clock signal voltage is applied, light absorption does not occur, and the optical signal passes through the semiconductor optical modulator without attenuation.

Therefore, when the optical signal shown in FIG. 3 (a) and the clock signal voltage shown in FIG. 3 (b) are applied, the current flowing through the semiconductor optical modulator becomes as shown in FIG. 3 (c). Thus, the optical output power output from the semiconductor optical modulator is as shown in FIG. FIG. 3C shows a current waveform corresponding to the optical signal obtained by dividing the optical signal shown in FIG. 3A by 1/2 time division. It is possible to extract an optical signal separated by a time division of 1/2 as a voltage waveform. The optical output waveform from the semiconductor optical modulator shown in FIG. 3 (d) is a 1/2 time-division separated optical waveform which is shifted by one bit from the current waveform shown in FIG. 3 (c). This optical waveform is received by a photodetector or the like and converted into a voltage waveform, whereby a 1/2 time-division separated voltage waveform shifted by one bit from the current waveform shown in FIG. 3C is obtained.

As described above, by using the semiconductor optical modulator as the time division light separation element of the time division light separation circuit, a small and highly reliable time division light separation circuit can be realized.

Next, the present invention will be described in more detail with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. The time division optical demultiplexing circuit according to the present embodiment performs time division demultiplexing of an optical signal 5 whose two data streams are time division multiplexed and whose data transmission speed is 20 Gb / s.

In FIG. 1, an optical signal 5 is inputted to a semiconductor optical modulator 1 whose optical absorptance changes when a voltage is applied and which converts absorbed light into a current. This semiconductor optical modulator 1
An optical signal 6 having a data transmission rate of 10 Gb / s and output through the optical input is input to a photodetector 2 using a PIN photodiode. The semiconductor optical modulator 1 has a clock voltage generator 7
10Gb / s clock signal voltage is applied, and this 10Gb / s
Is adjusted by the phase shifter 8. Resistors R _L1 and R _L2 for converting a current waveform into a voltage are connected to the semiconductor optical modulator 1 and the photodetector 2, respectively.
Further, wideband amplifiers 3 and 4 are connected to obtain a sufficient voltage amplitude.

Using the present embodiment, the phase of the clock signal voltage applied to the semiconductor optical modulator 1 is adjusted to an optimum value by the phase shifter 8, and the phase of the optical signal 5 having a wavelength of 1.55 μm and a data transmission speed of 20 Gb / s is obtained. When two-sequence time-division optical separation is performed, a good data-separated signal of 10 Gb / s free from code errors can be obtained from the amplifiers 3 and 4 even when the input power of the optical signal 5 is as small as −20 dBm.

FIG. 2 is a block diagram showing a second embodiment of the present invention. In this embodiment, the optical absorptance is changed by applying a voltage, and four semiconductor optical modulators 1, 11, 12, and 13 for converting the absorbed light into a current are optically cascaded to form four series. Is time-division-demultiplexed from the optical signal 5 in which the data of FIG. Each semiconductor optical modulator 1,11,12,13
The pulse width of the output of the clock voltage generator 7 is 40
A clock signal voltage of 5 Gb / s with an amplitude of 2 V at ps is applied, and the phase of these four clock signal voltages is adjusted to 50 ps by using phase shifters 8, 9, and 10. Has been adjusted to. The semiconductor optical modulators 1, 11, 12, and 13 have resistors R _L1 , R _L2 , R
_L3 , RL4 and amplifiers ₃ , _4, 16, 17 are connected.

Using this embodiment, when the time-division optical separation of the optical signal 5 in which the wavelength is 1.55 μm, the data transmission speed is 20 Gb / s, and the four series of data are time-division multiplexed, the light of the optical signal 5 is obtained. Even when the input power is as small as −23 dBm, a good data separation signal of 5 Gb / s without a code error can be obtained from each of the amplifiers 3, 4, 16, and 17.

As described above, the time division light splitting circuit of the present invention has been described using the two embodiments. However, the present invention can be applied to various aspects other than the above-described embodiments.

For example, although the time-division light separation circuit of this embodiment is configured using individual semiconductor optical modulators, integrating optical elements on the same substrate can increase the light coupling efficiency. Also,
The number of separations of the time-division light separation circuit is 2 in the two embodiments described above.
The number of streams is not limited to four, and can be any number.

When an optical amplifier or the like is used on the input side of the time division light separation circuit of the present invention, the sensitivity of the time division light separation circuit can be increased.

In the embodiment shown in FIG. 2, the semiconductor optical modulator 13 at the last stage may be the photodetector used in the embodiment shown in FIG.

(Effects of the Invention) As described above in detail, according to the present invention, by using a semiconductor optical modulator as a time division optical separation element of a time division optical separation circuit for optical data signals, a small and highly reliable A split light splitting circuit can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention, and FIG.
FIG. 3 is a block diagram showing a second embodiment of the present invention, and FIG. 3 is a diagram for explaining the operation of the semiconductor optical modulator used in the time division light splitting circuit of the present invention. 1,11,12,13 …… Semiconductor optical modulator, 2 …… Photodetector, 3,4,
16, 17 ... amplifier, 5, 6, 14, 15 ... optical signal, 7 ... clock voltage generator, 8, 9, 10 ... phase shifter.

Claims (2)

(57) [Claims] 1. A semiconductor optical modulator for converting an absorbed light into a current when a voltage is applied and converting the absorbed light into a current, and a light optically coupled with the semiconductor optical modulator and receiving the received light into a current. A time-division multiplexed optical signal is input to the semiconductor optical modulator, and 1 / N (N is a positive integer of 2 or more) of the data transmission rate of the optical signal. ), A clock signal voltage is applied to the photodetector, light transmitted through the semiconductor optical modulator is input to the photodetector, and the semiconductor optical modulator synchronizes the optical signal with the clock signal voltage from the optical signal. A time division optical separation circuit, wherein a bit signal is extracted as a current, and the remaining signal of the optical signal is extracted as a current from the photodetector. 2. A semiconductor optical modulator comprising: N semiconductor optical modulators for changing a light absorption rate when a voltage optically cascaded to an input optical signal is applied and converting the absorbed light into a current; The optical signal is an optical signal having a transmission rate of B obtained by time-division multiplexing of N data signals, and the N semiconductor optical modulators each have a clock signal voltage of 2π / N at a rate of B / N. A time-division optical separation circuit which is applied with a phase difference and extracts a data signal obtained by time-divisionally dividing the optical signal into 1 / N from the N semiconductor optical modulators as a current.