Optical routing system

An optical routing system where a time-division multiplexing signal train passes through a front stage semiconductor laser amplifier and detects information of a header and is multiplexed with a local oscillator light from a variable wavelength light source and passes through a rear stage semiconductor laser amplifier, and then is demultiplexed by an optical wavelength division demultiplexer and is outputted to an output side optical signal transmission fiber and an intermediate output port. Wavelength of the local oscillator light and selective wavelength of the optical wavelength division demultiplexer are selected so that a packet is outputted to an assigned intermediate output port. Thereby for the time-division multiplexing optical signal train, while the optical signal train as a whole is held, a specified part or a packet can be distributed.

BACKGROUND OF THE INVENTION 
The present invention relates to a time-division multiplexing optical 
signal transmission network and its switching node according to line 
switching system, packet switching system, ATM switching system or the 
like. 
Regarding an apparatus having optical distribution function in the prior 
art, as discussed in the spring symposium in 1990, C-220 of the 
electronics, information and communication engineers of Japan, a no-load 
1.times.4 optical gate switch constituted by five laser diode optical gate 
submodules and a 1.times.4 optical branch waveguide circuit is reported. 
Switching laser diode optical gate submodules are connected respectively 
to four output ends of the optical branch waveguide circuit, and one 
submodule for polarization compensation is connected to input end so that 
it has an activation layer surface vertical to other four gates. The 
submodule has structure that an optical gate of InGaAsP laser diode for 
1.3 .mu.m band and a single mode top-bulb optical fiber with top end 
radius 10 .mu.m installed on both ends of the optical disk are enclosed 
within a Cu-W cabinet, and coupling loss between the laser diode gate and 
the top-bulb optical fiber is 3 dB. The optical branch waveguide circuit 
is constituted by a quartz optical waveguide/Si and has 1.times.2 branch 
two-stage structure, and transmission loss between the fiber optical 
branch waveguide circuit and the fiber is 8 dB. Size of the whole switch 
is 12 mm.times.75 mm. Exciting current of 27-30 mA is applied to each 
laser diode optical gate thereby no-loss switching is realized. 
Since an optical gate switch of 1.times.(n-th power of 2) according to the 
same principle as that of the above-mentioned no-load 1.times.4 optical 
gate switch can be compensated in loss between input/output during 
switching by gain possessed by the contained laser diode optical gate, its 
application as distribution node in line switching system or a 
time-division multiplexing optical signal transmission network is being 
considered. In the above-mentioned no-load 1.times.4 optical gate switch, 
however, in addition to the deterioration quantity of S/N ratio (signal to 
noise strength ratio) in input/output side by the laser diode optical gate 
submodules before and after the optical branch waveguide circuit, it is 
further deteriorated by 8 dB due to the optical branch waveguide circuit. 
In general, in an optical gate switch of 1.times.(n-th power of 2), a 
problem exists in that the S/N ratio at the input/output side is 
deteriorated by (3.times.N) dB or more in principle due to the optical 
branch waveguide circuit. Five laser diode optical gate submodules are 
used in the no-load 1.times.4 optical gate switch, but laser diode optical 
gates of (n-th power of 2) pieces or more are necessary in the 1.times. 
(n-th power of 2) optical gate switch and a problem exists also in that an 
optical gate switch of small size and large scale cannot be easily 
realized. Further considering application as distribution node in the 
time-division multiplexing optical signal transmission network by packet 
switching system, ATM switching system or the like, in the optical gate 
switch of 1.times. (n-th power of 2), since a specific packet cannot be 
distributed while optical signal train as a whole is held, if this is 
connected in cascade, one packet cannot be distributed from the 
distribution nodes of two positions or more, or similar problem exists in 
that the use state is limited. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a method which can 
distribute a specified packet where deterioration of the S/N ratio in the 
input/output side is little even if the distribution number is increased, 
or a number of optical active elements are not required and while optical 
signal train as a whole is preserved, in an optical routing system capable 
of being applied as distribution node in a time-division multiplexing 
optical signal transmission node by line switching system, a packet 
switching system, ATM switching system or the like. 
In order to attain the foregoing object, in the present invention, 
time-division multiplexing optical signal train is multiplexed with single 
or plural local oscillator lights and then incident to a semiconductor 
laser amplifier, and lights emitted from the semiconductor laser amplifier 
are incident to an optical wavelength division demultiplexer. The 
demultiplexer is designed so that lights having the same wavelength as 
that of the optical signal train are emitted to an optical signal 
transmission fiber at the output side, and lights having single or plural 
wavelengths being different from that of the optical signal train are 
emitted to single or plural intermediate output ports in one-to-one 
correspondence with the wavelength. Wavelength of single or plural local 
oscillator lights is selected to wavelength in one-to-one correspondence 
with an intermediate output port to be outputted as above described, 
thereby the optical signal train as a whole can be distributed to an 
optical signal transmission fiber at output side and an arbitrary part can 
be distributed to assigned single or plural output ports. 
Particularly for a time-division multiplexing optical signal train by 
packet switching system, ATM switching system or the like, a part of 
optical signals within each packet is branched by an optical branching 
device and information regarding a destination of the packet stored in the 
header is read by the light receiver. Or two semiconductor laser 
amplifiers are used and each packet passes through the semiconductor laser 
amplifier at the front stage thereby the information is read. According to 
the information, the local oscillator lights are emitted by the time while 
each packet passes. After passing through the optical power splitter or 
the semiconductor laser amplifier at the front stage, each packet passes 
through a delay line and then is multiplexed with the local oscillator 
lights. Here, length of the delay line is determined so that the time 
required to pass through the delay line is equal to the time of the header 
from being incident to the light receiver or the semiconductor laser 
amplifier at the front stage until operating the local oscillator lights. 
Thereby the optical signal train as a whole can be distributed in the 
optical signal transmission fiber at the output side and an arbitrary 
packet can be distributed to single or plural intermediate output ports 
assigned by the header. 
Time-division multiplexing optical signals being incident to the 
semiconductor laser amplifier modulate the carrier density in the 
semiconductor laser amplifier. That is, when strength of the optical 
signal is large, consumption of the carrier is large and the carrier 
density is decreased. On the other hand, when strength of the optical 
signal is small, consumption of the carrier is small and decrease of the 
carrier density is little. Gain received by single or plural local 
oscillator lights being incident together with the optical signals within 
the semiconductor laser amplifier becomes high when the carrier density is 
large, and it becomes low or is transferred to loss when the carrier 
density is small. Therefore the local oscillator lights are subjected to 
strength modulation into inverted state of the optical signals. When the 
optical signals and the local oscillator lights are incident to the 
optical wavelength division demultiplexer, due to the demultiplexer, the 
optical signals are emitted to the optical signal transmission fiber at 
the output side, and the single or plural local oscillator lights having 
wavelength different from that of the optical signal train are emitted to 
single or plural intermediate output ports in one-to-one correspondence 
with the wavelength. Thereby the optical signal train as a whole is 
distributed to the optical signal transmission fiber at the output side, 
and an arbitrary part is distributed to assigned single or plural 
intermediate output ports. 
Particularly for a time-division multiplexing optical signal train by 
packet switching system, ATM switching system or the like, information 
regarding a destination of the packet stored in the header of each packet 
can be read by the light receiver. Also when two semiconductor laser 
amplifiers are used, when the header of each packet passes through the 
semiconductor laser amplifier at the front stage, since the terminal 
voltage is modulated, information regarding a destination of each packet 
can be read from the modulation signal. According to the information, the 
local oscillator lights are emitted by the time while each packet passes. 
After passing through the delay line, each packet is incident to the 
optical wavelength division multiplexer simultaneously with the local 
oscillator lights and is multiplexed. After passing through the 
semiconductor laser amplifier, the local oscillator lights subjected to 
the strength modulation into the inverted state and the optical signals 
are incident to an optical wavelength division demultiplexer, and by the 
demultiplexer, the optical signal train as a whole is distributed to the 
optical signal transmission fiber at the output side, and an arbitrary 
packet is distributed to single or plural intermediate output parts 
assigned by the header.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A first embodiment of the present invention is shown in FIG. 1. FIG. 1 is a 
constitution diagram of an optical routing system, and an inverted signal 
of an arbitrary packet in a time-division multiplexing optical signal 
train inputted from a transmission path connected to the input side of the 
optical routing system can be outputted to an intermediate output port 
corresponding to information written in a header of the packet, and at the 
same time the optical signal train as a whole can be outputted to a 
transmission path connected to the output side. In FIG. 1, numeral 1 
designates an input side optical signal transmission fiber, numeral 2 
designates a front stage semiconductor laser amplifier, numeral 3 
designates a delay line, numeral 4 designates an optical wavelength 
division multiplexer, numeral 5 designates a rear stage semiconductor 
laser amplifier, numeral 6 designates an optical wavelength division 
demultiplexer, numeral 7 designates an output side optical signal 
transmission fiber, numerals 8A, 8B, 8C designate intermediate output 
ports, numeral 9 designates a variable wavelength light source controlling 
circuit, and numeral 10 designates a variable wavelength light source. 
Original optical signal train of wavelength .lambda..sub.0 in 
time-division multiplexing of a number of packets is inputted from the 
input side optical signal transmission fiber 1. Passing through the front 
stage semiconductor laser amplifier 2 to which definite voltage is applied 
in the forward direction, the terminal voltage is modulated by the 
original optical signal train. The modulated signal is transmitted to the 
variable wavelength light source controlling circuit 9. In the header of 
each packet is stored information relating to a destination of the packet, 
that is, information determining either to which of the intermediate 
output ports 8A, 8B, 8C should be outputted the packet, or to any of the 
intermediate output ports 8A, 8B, 8C should not be outputted the packet. 
According to the information, the variable wavelength light source 
controlling circuit 9 operates the variable wavelength light source 10, 
and local oscillator lights of definite output are emitted at wavelength 
in one-to-one correspondence with the destination of the packet. 
Wavelength of the local oscillator lights shall be .lambda..sub.A, 
.lambda..sub.B, .lambda..sub.C when the destination of the packet is the 
intermediate output ports 8A, 8B, 8C. However, if the packet is not 
outputted to any of the ports 8A, 8B, 8C, no local oscillator light will 
be emitted. Definite time delay is generated from the header passes 
through the front stage semiconductor laser amplifier 2 until the variable 
wavelength light source 10 emits the local oscillation lights, but length 
of the delay line 3 is determined precisely-so that the original optical 
signal passing through the front stage semiconductor laser amplifier 2 
spends the same time to pass through the delay line 3. Therefore the 
header passing through the delay line 3 and the local oscillator light are 
simultaneously incident to the optical wavelength division multiplexer 4 
and multiplexed, and then incident to the rear stage semiconductor laser 
amplifier 5 to which definite voltage is applied in the forward direction. 
Carrier density in the rear stage semiconductor laser amplifier 5 is 
modulated by the original optical signal within the packet, and the local 
oscillator light is modulated into its inverted signal. The original 
optical signal and the modulated local oscillator light are emitted from 
the rear stage semiconductor laser amplifier 5 and then incident to the 
optical wavelength division demultiplexer 6. The optical wavelength 
division demultiplexer 6 is designed so as to emit lights of wavelength 
.lambda..sub.0 to the output side optical signal transmission fiber 7 and 
lights of wavelength .lambda..sub.A, .lambda..sub.B, .lambda..sub.C to the 
intermediate output ports 8A, 8B, 8C. Therefore the original optical 
signal within the packet is outputted to the output side optical signal 
transmission fiber 7, and its inverted signal is either outputted to any 
of the intermediate output ports 8A, 8B, 8C in response to the destination 
written in the header or not outputted to any of the ports 8A, 8B, 8C. 
The front stage semiconductor laser amplifier 2 and the rear state 
semiconductor laser amplifier 5 have the inner gain 28 dB, when the 
exciting current is 150 mA, and the optical coupling degree at the 
input/output side is -3.5 dB and the gain between fibers is 21 dB. In the 
variable wavelength light source controlling circuit 9, a variable 
wavelength distribution Bragg reflection type laser module having three 
electrodes is applied. The fiber light output is set to -16 dBm, and the 
variable width of wavelength is from 1509 nm to 1512.5 nm, i.e., 3.5 nm or 
more. The variable wavelength light source controlling circuit 9 is 
designed so that the variable wavelength light source 10 is oscillated 
with definite output by 176.7 ns in wavelength 1511, 1512, 1513 nm for 
three sorts of input signals 0001, 0010, 0011. The optical wavelength 
division demultiplexer 6 is constituted by combination of three pieces of 
1:1 optical WDM couplers by a Mach-Zehnder interferometer. A first coupler 
has an input port I1 and output ports O1, O2. The demultiplexing interval 
is 1 nm, and selective interval of the output port O1 is 1510, 1512, 1514 
. . . 1550, 1552 . . . nm, and selective wavelength of the output port O2 
is 1511, 1513, 1515 . . . nm. A second coupler has an input port I2 and 
output ports O3, O4. The demultiplexing interval is 2 nm, and selective 
wavelength of the output port O3 is 1512, 1516 . . . nm, and selective 
wavelength of the output port O4 is 1510, 1514 . . . nm. A third coupler 
has an input port I3 and output ports O5, O6. The demultiplexing interval 
is 2 nm, and selective wavelength of the output port O5 is 1513, 1515 . . 
. nm, and selective wavelength of the output port O6 is 1511, 1515 . . . 
nm. Any of the 1:1 optical WDM couplers has insertion loss of selective 
wavelength being -1 dB and crosstalk being -20 dB. The output ports O1, O2 
are connected to the input ports I2, I3 thereby the optical wavelength 
division demultiplexer 6 is constituted. If the optical signals of 
wavelength 1511, 1512, 1513, 1550 nm are incident to the input port I1, 
the optical signals of wavelength 1511, 1512, 1513, 1550 nm are outputted 
from the output ports O6, O3, O5, O4. Insertion loss of selective 
wavelength of the optical wavelength division demultiplexer 6 is -3 dB, 
and the crosstalk is -16 dB. The output ports O6, O3, O5 and O4 are 
connected to the intermediate output ports 8A, 8B, 8C and the output side 
optical signal transmission fiber 7. In the optical wavelength division 
multiplexer 4, a non-polarization beam splitter is used. 
Packet multiplexing optical signal train with wavelength .lambda..sub.0 
being 1.55 .mu.m and optical output level in peak value being -20 dB is 
inputted to the optical routing system. Optical signals within the packet 
are NRZ modulation signals with the transmission speed 2.4 Gb/s and the 
mark ratio 1/2. Each packet has a header of 5 bytes and an information 
part of 48 bytes. To the header of each packet are allocated control 
signals of 0001, 0010, 0011, 0000 in this order repeatedly. If the control 
signals of the header are 0001, 0010, 0011, inverted signals of the 
optical signals within each packet are obtained to the intermediate output 
ports 8A, 8B, 8C, and at the same time the optical signals within each 
packet are outputted to the output side optical signal transmission fiber 
7. Optical output level in the peak value of each inverted signal is 0 
dBm, and "1", "0" level ratio is -15 dB or more. Optical output level in 
the peak value of the optical signal transmission fiber 7 is 3 dBm. If the 
control signal of the header is 0000, only the optical signal within each 
packet is outputted to the output side optical signal transmission fiber 
7, and the optical output level in the peak value is 3 dBm. 
A second embodiment of the present invention is shown in FIG. 2. FIG. 2 is 
a constitution diagram of an optical routing system, and inverted signals 
of an arbitrary packet in a time-division multiplexing optical signal 
train inputted from a transmission path connected to the input side of the 
optical routing system can be outputted to intermediate output ports of 0, 
1, 2, 3 or 4 pieces corresponding to information written in a header of 
the packet, and at the same time the optical signal train as a whole can 
be outputted to a transmission path connected to the output side. In FIG. 
2, numeral 11 designates an optical power splitter, numeral 12 designates 
an optical wavelength division multiplexer, numeral 13 designates an 
optical wavelength division demultiplexer, numeral 14 designates an 
intermediate output port, numeral 15 designates a light receiver, numeral 
16 designates a local oscillator light source group, and numeral 18 
designates a semiconductor laser amplifier. There are 16 pieces of the 
intermediate output ports, and the local oscillator light source group 17 
is constituted by 16 pieces of local oscillator light sources and 
wavelength of a light emitted from each local oscillator light source is 
in one-to-one correspondence with each intermediate output port. In 
similar manner to the first embodiment, an original optical signal train 
of wavelength .lambda..sub.0 with a number of packets in time-division 
multiplexing is inputted from the input side optical signal transmission 
fiber 1. A part is branched by the optical power splitter 11 and received 
by the light receiver 15. The received signal is transmitted to the local 
oscillator light source group controlling circuit 16. In the header of 
each packet is stored information relating to a destination of the packet, 
that is, information determining either to which of the intermediate 
output ports 14 should be outputted the packet, or to any of the 
intermediate ports 14 should not be outputted the packet. According to the 
information, the local oscillation light source group controlling circuit 
16 operates one or plural local oscillator light sources among the local 
oscillator light source group 17, and local oscillator lights are emitted. 
However, when the destination of the packet is the i-th (i is integer of 
1-16) intermediate output port, the local oscillator light source having 
wavelength .lambda..sub.i is operated and the local oscillator light is 
emitted. If the packet is not outputted to any of the ports, no local 
oscillator light is emitted. After the packet passes through the delay 
line 3, the header and each local oscillator light are incident 
simultaneously to the optical wavelength division multilexer 12 and 
multiplexed, and then incident to the semiconductor laser amplifier 18 to 
which definite voltage is applied in the forward direction. In similar 
manner to the first embodiment, length of the delay line 3 is determined 
precisely so that the time delay from the header being branched by the 
optical power splitter 11 until the local oscillator light source group 17 
emitting the local oscillator light can be compensated. The carrier 
density in the semiconductor laser amplifier 18 is modulated by the 
original optical signals within the packet, and each local oscillator 
light is modulated to the inverted signal. The original optical signal and 
each modulated local oscillator light are emitted from the semiconductor 
laser amplifier 18, and then incident to the optical wavelength division 
demultiplexer 13. The optical wavelength division demultiplexer 13 is 
designed so that light with wavelength 20 is emitted to the output side 
optical signal transmission fiber 7 and light with wavelength 
.lambda..sub.i is emitted to the i-th intermediate output port 14. 
Therefore the original optical signal within the packet is outputted to 
the output side optical signal transmission fiber 7, and the inverted 
signal is outputted to the intermediate output ports 14 of 0, 1, 2, 3 or 4 
pieces in response to the destination written in the header. 
The semiconductor laser amplifier 18 has the inner gain 28 dB, when the 
exciting current is 150 mA, and the optical coupling degree at the 
input/output side is -3.5 dB and the gain between fibers is 21 dB. The 
local oscillator light source 17 is constituted by 16 pieces of 
semiconductor laser modules where the oscillation wavelength is set in 
interval of 1 nm from 1523 nm to 1538 nm. The fiber light output is set to 
each -16 dBm. The local oscillator light source 16 is designed so that the 
selected local oscillator light source 17 is oscillated in definite output 
by 176.7 ns, for the input signals 000000000000, 000000000001 . . . 
100111010101 of sorts corresponding to the number when 0, 1, 2, 3 or 4 
pieces are selected from 16 pieces of the intermediate output ports 14, 
i.e., .sub.16 C.sub.0 +.sub.16 C.sub.1 + . . . +.sub.16 C.sub.4 =2517. The 
optical wavelength division demultiplexer 13 is constituted in combination 
of a slab waveguide having converging function with an array waveguide 
diffraction grating and an input/output waveguide. The array waveguide 
diffraction grating is constituted by 201 pieces of waveguides where 
optical path length difference between the neighboring waveguides is 37.14 
.mu.m. It has one input port and 28 output ports, and selective wavelength 
of each output port is distributed in interval of 1 nm from 1523 nm to 
1550 nm. Insertion loss of the selective wavelength of each output port is 
-5-7 dB and the crosstalk is -15 dB. Each output port with selective 
wavelength from 1523 nm to 1538 nm is connected to the first to sixteenth 
intermediate output ports 14 in one-to-one correspondence, and the output 
port with selective wavelength being 1550 nm is connected to the output 
side optical signal transmission fiber 7. The optical wavelength division 
multiplexer 12 is constituted by that same as the optical wavelength 
division demultiplexer 13 in changing between the input side and the 
output side. Each input port filth selective wavelength from 1523 nm to 
1538 nm is connected in one-to-one correspondence to 16 pieces of the 
semiconductor laser modules with oscillation wavelength from 1523 nm to 
1538 nm among the local oscillator light source group 17, and the input 
port with selective wavelength being 1550 nm is connected-to the output 
side fiber of the semiconductor laser amplifier 18. 
The packet multiplexing optical signal train with the wavelength 
.lambda..sub.0 being 1.55 .mu.m and the light output level in the peak 
value being 8 dB is inputted to the optical routing system. The optical 
signals within the packet are NRZ modulation signals with the transmission 
speed being 2.4 Gb/s and the mark ratio being 1/2. Each packet has a 
header of 5 bytes and an information port of 48 bytes. The control signals 
of 000000000000, 000000000001 . . . 100111010101 of 2517 sorts selecting 
0, 1, 2, 3 or 4 pieces among 16 pieces of the intermediate output ports 14 
are allocated in this order repeatedly to the header of each packet. In 
response to the control signal of the header, an inverted signal of an 
optical signal within each packet is obtained, and at the same time, the 
optical signal within each packet is outputted to the output side optical 
signal transmission fiber 7. The light output level in the peak value of 
each inverted signal is -9--10 dBm, and the "1", "0" level ratio is -15 dB 
or more. The light output level in the peak value of the optical signal 
outputted to the output side optical signal transmission fiber 7 is -1 
dBm. 
An embodiment of a time-division multiplexing optical transmission network 
using the optical routing system of the first and second embodiments is 
shown in FIG. 3. In FIG. 3, numeral 21 designates a light transmitter, 
numeral 22 designates an optical routing system in the first embodiment, 
numeral 23 designates an optical routing system in the second embodiment, 
numeral 24 designates a light amplifier, numeral 25 designates a single 
mode optical fiber for transmission, numeral 26 designates an optical 
regenerative repeater, and numerals 27a-27m designate light receivers. The 
light transmitter 21 can transmit a packet multiplexing optical signal 
train of wavelength 1550 nm constituted by NRZ modulation signals having 
transmission speed 2.4 Gb/s, wavelength 1550 nm and mark ratio 1/2. The 
fiber light output is set in mean light output level being -3 dBm. The 
single mode optical fiber 25 for transmission is a zero-dispersion shift 
fiber of 1550 mn band, and the transmission loss is 0.2 dB/km. The light 
amplifier 24 is a fiber light amplifier which carries out light 
amplification by an erbium added optical fiber subjected to bidirectional 
optical excitation by a semiconductor laser of wavelength 1480 nm. Each 
exciting input to the fiber of the semiconductor laser is 34 mW, and the 
maximum gain is 33 dB and the compression output of the 3 dB gain is 12 
dBm. Each of the light receivers 27a-27m is constituted by a preamplifier 
IC containing InGaAs-APD module, an equalization amplifier circuit, a 
timing extraction circuit, a discrimination reproducing circuit, and the 
maximum light receiving power is -32 dBm in the error ratio 10.sup.-11. 
The optical regenerative repeater 26 is constituted in combination of the 
light receiver 27 and the light transmitter 24, and has 3R functions, that 
is, functions of equalization amplifying, retiming and discrimination 
reproducing. The minimum light receiving power is -32 dBm in the error 
ratio 10.sup.-11, and the mean light output level is -3 dBm. In order to 
transmit different signals to the light receivers 27a-27m, 13 sorts of the 
packets A-M in this order are subjected to time-division multiplexing 
repeatedly. Each packet has a header of 5 bytes and an information part of 
48 bytes. Control signals of 0001, 0010 . . . 1101 are allocated as a 
destination of the packet to the header of each of the packets A-M. The 
optical routing system 22 in the first embodiment is set so that the 
control signals of the header output the packets of 0001, 0010, 0011 to 
each intermediate output port to which the light receivers 27a, 27b, 27c 
are connected. The optical routing system 23 in the second embodiment is 
set so that the control signals of the header output the packets of 0001, 
0101 . . . 1101 to the intermediate output ports of 1-4 pieces to which 
the light receivers 27d, 27e . . . 27m are connected. Length of the single 
mode optical fiber 25 for transmission shall be made 100 km between the 
light transmitter 21 and the optical routing system 22 in the first 
embodiment, 115 km between the optical routing system 22 in the first 
embodiment, 100 km between the optical routing system 22 in the first 
embodiment and the optical regenerative repeater 26, 125 km between the 
optical regenerative repeater 26 and the light amplifier 24, 100 km 
between the optical routing system 23 in the second embodiment and the 
light receivers 27a, 27b . . . 27e, 80 km between the optical routing 
system 22 in the first embodiment and the light receivers 27a, 27b . . . 
27e, and 50 km between the optical routing system 23 in the second 
embodiment and the light receivers 27d, 27e . . . 27m. As a result of 
transmitting the packet multiplexing optical signal train from the light 
transmitter 21, optical signals within the packets A-M are received in a 
number of light receivers 27a-27m respectively, and clear eye patterns are 
obtained. 
A fourth embodiment of the present invention is shown in FIG. 4. FIG. 4 is 
a constitution diagram of a packet switching apparatus. An arbitrary 
packet in a time-division multiplexing optical signal train inputted from 
a transmission path connected to the input side of the packet switching 
apparatus is stored again in an arbitrary time slot, on the premise that 
two or more packets are not stored in one time slot, and then the stored 
packet is outputted from an intermediate output port and the optical 
signal train itself can be outputted to a transmission path connected to 
the output side. In FIG. 4, numeral 31 designates a variable wavelength 
light source group, numerals 32a-32g designate delay lines, and numeral 33 
designates an intermediate output port. A time-division multiplexing 
optical signal has wavelength .lambda..sub.0 and four time slots, and a 
packet is stored in each time slot. The optical signal train is inputted 
from an input side optical signal transmission fiber 1. Passing through a 
front stage semiconductor laser amplifier 2 to which definite voltage is 
applied in the forward direction, the terminal voltage is modulated by the 
original optical signal train. The modulated signal is transmitted to a 
variable wavelength light source controlling circuit 9. In a header of 
each packet is stored information regarding to what number of a time slot 
is stored the packet at present and next to what number of a time slot 
should be stored again the packet. According to the information, the 
variable wavelength light source controlling circuit 9 operates the 
variable wavelength light source group 31, and local oscillator lights of 
definite output are emitted in wavelength in one-to-one correspondence 
with moving amount of a time slot in which the packet is to be stored. 
Wavelength of the local oscillator lights shall be .lambda..sub.1, 
.lambda..sub.2 . . . .lambda..sub.7 if the moving amount corresponds to 
the time slots of 1, 2 . . . 7 pieces. After the packet passes through the 
delay line 3, the header and the local oscillator light are incident to an 
optical wavelength division multiplexer 4 simultaneously and multiplexed, 
and then incident to a rear stage semiconductor laser amplifier 5 to which 
definite voltage is applied in the forward direction. In similar manner to 
the first embodiment, length of the delay line 3 is determined precisely 
so that the time delay from the header passing through the front stage 
semiconductor laser amplifier 2 until the variable wavelength light source 
group 31 emitting the local oscillator light can be compensated. Carrier 
density in the rear stage semiconductor laser amplifier 5 is modulated by 
the original optical signal within the packet, and the local oscillator 
light is modulated to the inverted signal. The original optical signal and 
the modulated local oscillator light are emitted from the rear stage 
semiconductor laser amplifier 5 and then incident to the optical 
wavelength division demultiplexer 13. The optical wavelength division 
demultiplexer 13 is designed so that light with wavelength .lambda..sub.0 
is emitted to the output side optical signal transmission fiber 7 and 
lights with wavelength .lambda..sub.1, .lambda..sub.2 . . . .lambda..sub.7 
are emitted to the delay lines 32a, 32b . . . 32g. Length of each of the 
delay lines 32a, 32b . . . 32g is determined precisely so that time 
corresponding to each of the time slots of 1, 2 . . . 7 pieces is required 
for the optical signal train to pass through the delay lines 32a, 32b . . 
. 32g. The delay lines 32a, 32b . . . 32g are multiplexed by the optical 
wavelength division multiplexer 12 and outputted to the intermediate 
output port 33. According to the above-mentioned constitution, an optical 
signal train with an arbitrary time slot can be obtained from the 
intermediate output port 33. 
The variable wavelength light source group 31 is constituted using two 
variable wavelength distribution Bragg reflection type laser modules each 
having three electrodes, and each wavelength variable width is 1523-1526 
nm and 1527-1529 nm and by changing both, wavelength of 1523-1529 nm can 
be selected. The fiber light output is -16 dBm. The variable wavelength 
light source controlling circuit 9 is designed so that when the packet is 
stored in the i-th time slot at present and should be stored again in the 
j-th time slot next and j - i is -3, -2, -1, 0, 1, 2, 3, the variable 
wavelength light source group 31 is oscillated at definite output by 176.7 
ns in wavelength 1523, 1524, 1525, 1526, 1527, 1528, 1529 nm. Among output 
ports of the optical wavelength division demultiplexer, each output port 
with selective wavelength from 1523 nm to 1529 nm is connected to the 
delay lines 32a, 32b . . . 32g, and an output port with selective 
wavelength 1550 nm is connected to the output side optical signal 
transmission fiber 7. 
A packet multiplexing optical signal train with wavelength .lambda..sub.0 
being 1.55 .mu.m and light output level in the peak value being -20 dBm is 
inputted in the optical routing system. The optical signal train has four 
time slots, and a packet is stored in each time slot. An optical signal 
within the packet is NRZ modulation signal with transmission speed being 
2.4 Gb/s and mark ratio being 1/2. Each packet has a header of 5 bytes and 
an information part of 48 bytes. The number of the time slot storing the 
packet at present is allocated to the first byte of the header of each 
packet, and the number of the time slot to store the packet next is 
allocated to the second byte. In order that the packets in the first, 
second, third and fourth time slots are stored again in the fourth, 
second, third and first time slots, each of the control signals of 
00010100, 00100010, 00110011, 01000001 is allocated. Inverted signals with 
packets in the first, second, third and fourth time slots among the packet 
multiplexing optical signal train being stored again in the fourth, 
second, third and first time slots are obtained from the intermediate 
output port 33, and at the same time the inputted packet multiplexing 
optical signal train is outputted to the output side optical signal 
transmission fiber 7. The light output level in the peak value of each 
inverted signal is -15 dB or more. The light output level in the peak 
value of the optical signal outputted to the output side optical signal 
transmission fiber 7 is -1 dBm. 
An embodiment of an optical switch using the packet switching apparatus in 
the fourth embodiment is shown in FIG. 5. In FIG. 5, numerals 41a-41b 
designate optical switches, numerals 42a, 42b designate packet switching 
apparatuses in the fourth embodiment, numerals 43a, 43b designate input 
side optical signal transmission fibers, and numerals 44a, 44b designate 
output side optical signal transmission fibers. A packet multiplexing 
optical signal train to be inputted or outputted has four time slots, and 
a packet is stored in each time slot. In a packet multiplexing optical 
signal train inputted from the input side optical signal transmission 
fiber 43a, by the optical 41a, packets in the first and third time slots 
are inputted to the packet switching apparatus 42a of the fourth 
embodiment, and packets in the second and fourth time slots are inputted 
to the packet switching apparatus 42b of the fourth embodiment. In a 
packet multiplexing optical signal transmission fiber 43b, by the optical 
switch 41a, packets in the first and third time slots are inputted to the 
packet switching apparatus 42b of the fourth embodiment, and packets in 
the second and fourth time slots are inputted to the packet switching 
apparatus 42a of the fourth embodiment. In the packet switching 
apparatuses 42a, 42b of the fourth embodiment, inverted signals within 
each slot are stored again in the assigned time slot. In the inverted 
signal outputted from the intermediate output of the packet switching 
apparatus 42a of the fourth embodiment, by the optical switch 41b, packets 
in the first and third time slots are outputted to the output side optical 
fiber 44a, and packets in the second and fourth time slots are outputted 
to the output side transmission fiber 44b. In the inverted signal 
outputted from the intermediate output port of the packet switching 
apparatus 42b of the fourth embodiment, by the optical switch 41b , 
packets in the first and third time slots are outputted to the output side 
optical signal transmission fiber 44b, and packets in the second and 
fourth time slots are outputted to the output side optical signal 
transmission fiber 44a. 
The optical switches 41a, 41b are LiNbO.sub.3 2.times.2 optical switches, 
and insertion loss between input/output ports is 1-2 dB and extinction 
ratio is 20-25 dB. A packet multiplexing optical signal train with 
wavelength .lambda..sub.0 being 1.55 .mu.m and light output level in the 
peak value being -18 dBm is inputted to the input side optical signal 
transmission fibers 43a, 43b of the optical switch. The optical signal 
train has four time slots, and a packet is stored in each time slot 
optical signals within the packet are NRZ modulation signals of 
transmission speed 2.4 Gb/s and mark ratio 1/2. Each packet has a header 
of 5 bytes and an information part of 48 bytes. The number of the time 
slot storing the packet at present is allocated to the first byte of the 
header of each packet, and the number of the time slot to store the packet 
next is allocated to the second byte. Study has been carried out in the 
case that among packets inputted from the input side optical signal 
transmission fiber 43a, packets in the first and fourth time slots are 
outputted to the output side optical signal transmission fiber 44b, and 
other packets are outputted to the output side optical signal transmission 
fiber 44a, and that among packets inputted from the input side optical 
signal transmission fiber 43b, packets in the first and fourth time slots 
are outputted to the output side optical signal transmission fiber 44a, 
and other packets are outputted to the output side optical signal 
transmission fiber 44b. Each of the control signals 00010100, 00100010, 
00110011, 01000001 is allocated to header of packets in the first, second, 
third and fourth time slots inputted from the input side optical signal 
transmission fibers 43a, 43b. Packets in the first, second, third and 
fourth time slots inputted to the packet switching apparatuses 42a, 42b of 
the fourth embodiment are together stored again in the fourth, second, 
third and first time slots. Inverted signals within packets in the first 
and fourth time slots inputted from the input side optical signal 
transmission fiber 43a and within packets in the second and third time 
slots inputted from the input side optical signal transmission fiber 43b 
are outputted to the output side optical signal transmission fiber 44b, 
and inverted signals within packets in the second and third time slots 
inputted from the input side optical signal transmission fiber 43a and 
within packets in the first and fourth time slots inputted from the input 
side optical signal transmission fiber 43b are outputted to the output 
side optical signal transmission fiber 44a. Light output level in the peak 
value of each inverted signal is -12--13 dBm, and the "1", "0" level ratio 
is 15 dB or more. 
According to the present invention, in an optical routing system to be 
applied as distribution node in a time-division multiplexing optical 
signal transmission network according to line switching system, ATM 
switching system or the like, even if the distribution number is 
increased, deterioration of S/N ratio at input/output side is little or a 
number of optical active elements are not required and while an optical 
signal train as a whole is preserved a specified part or a packet can be 
distributed, thereby a time-division multiplexing optical transmission 
network according to line switching system of large scale and high speed 
or packet switching system, ATM switching system or the like can be 
constituted by relatively free layout and low cost, and application to 
optical communication network in subscriber system or repeating system or 
optical local area network becomes possible.