JPH09237929A - Method and apparatus for sampling optical clock - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to output both fundamental clock frequencies and trains of optical clock pulses with frequencies of integral multiples of the fundamental clock frequency using one optical clock sampling device. SOLUTION: An optical pulse data string S1 having a clock frequency equal to the cycling frequency of the light of mode-locked semiconductor laser 1 or a clock frequency of an integral multiple thereof, is raputted. Bias conditions for the oversaturation absorbing regions 11a, 11b and the gain regions 12a-12c of the modelocked semiconductor laser 1 are varied, and it is thereby made possible to output a train S2 of optical clock pulses with the clock frequency of the optical pulse data string S1 taken as a repetition frequency. This makes it possible to obtain a frequency f and a train of optical clock pulses with a frequency mf of an integral multiple thereof using one optical clock sampling device.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical clock extraction method and an extraction device which are used in ultrahigh-speed optical communication and which can output an optical clock pulse train of the clock frequency from input optical pulse data.

[0002]

2. Description of the Related Art In ultra-high-speed optical communication, which has been developed in recent years, in order to avoid the limitation of the processing speed of the electric signal when converting the optical signal into the electric signal and performing the signal processing, the optical pulse data train is used. A technique for directly generating an optical clock pulse train is required. Conventionally, as an optical clock extraction device of this type, there is a technique described in Japanese Patent Laid-Open No. 6-13981. This technique uses a passive mode-locking semiconductor laser composed of a saturable absorption region and a gain region, and an optical pulse data train has a fundamental mode-locking frequency (optical frequency in a resonator) almost the same as its clock frequency f. When the laser beam is incident on a passive mode-locking semiconductor laser having an orbital frequency of 1), the mode-locking frequency of the passive mode-locking semiconductor laser becomes the clock frequency f of the incident laser light under the mode-locking operation conditions or conditions close thereto. Thus, the optical clock pulse train of frequency f is obtained as an optical output.

[0003]

By the way, in the application in optical communication, one optical clock extraction device converts optical clock data of a clock frequency f and an integer multiple of the clock frequency from the optical pulse data train, that is, the frequency. f
And it is desired to obtain an optical clock pulse train having a clock frequency of the integral multiple frequency mf. However, the technique described in the above publication cannot obtain an optical clock pulse train from an optical pulse data train having a clock frequency that is an integral multiple of the fundamental mode-locking frequency f in the passive mode-locking semiconductor laser. It is because the passive mode-locking semiconductor laser has a self-modulation function of a fundamental mode-locking frequency f.
This is because the optical pulse train having an integral multiple of the clock frequency f cannot enjoy stable reproduction and amplification support in the resonator. That is, this is because only the frequency component synchronized with the self-modulation frequency is enhanced. For this reason, conventionally, a plurality of optical clock extraction devices corresponding to individual clock frequencies are required, which causes a problem that the equipment for optical communication is increased and the cost is increased.

An object of the present invention is to provide an optical clock extraction method and an optical clock extraction method capable of outputting an optical clock pulse train having a basic clock frequency and a clock frequency that is an integral multiple of the basic clock frequency with one optical clock extraction apparatus. It is in.

[0005]

According to the optical clock extraction method of the present invention, the input light is input as an optical pulse data train having a clock frequency substantially equal to the circulating frequency of the light of the mode-locked semiconductor laser or an integer multiple thereof. It is characterized in that the bias condition applied to the mode-locked semiconductor laser is changed based on the clock frequency, and the optical clock pulse train having the clock frequency of the optical pulse data train as the repetition frequency is output.

Further, the optical clock extraction device of the present invention, the input means for guiding the input light, the mode-locked semiconductor laser to which this input light is input, and the output light from this mode-locked semiconductor laser are sent to the external optical circuit. The mode-locked semiconductor laser has 1 / m of its cavity length.
When the saturable absorption region is arranged at a position (m is an integer) and an optical pulse data train having a clock frequency m times the optical circulation frequency in the resonator is incident, the saturable absorption region is reversed to the saturable absorption region. A feature is that a bias is applied.

Further, it is preferable that the optical clock extraction device has the following configuration. That is, in the mode-locked semiconductor laser, a plurality of saturable absorption regions and gain regions corresponding to different m values are arranged, and the clock frequency is m times as large as the optical orbital frequency in the resonator. When the optical pulse data train of is incident, the saturable absorption region arranged at the position having the same m value is set as the reverse bias, and the other saturable absorption region and the gain region are set as the forward bias. To be In this case, the first saturable absorption region is arranged at a position L / m1 with respect to the cavity length L from the incident end face of the mode-locking semiconductor laser, and L / m2 (m1, The second saturable absorption region is arranged at a position (m2 is a different integer). Further, a saturable absorption region may be arranged at the incident end face position of the mode-locked semiconductor laser.

[0008]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a conceptual block diagram of an optical clock extraction device of the present invention. The optical clock extraction device is mainly composed of a mode-locked semiconductor laser 1, an input circuit 1X for inputting optical pulse data to the input side of the mode-locked semiconductor laser 1 is provided, and an optical clock pulse train is output to the output side. The output circuit 1Y is provided. The mode-locked semiconductor laser 1 includes a substrate 17 and an N-type cladding layer 1.
6, active layer 15, P-type clad layer 14, cap layer 13
The cap layers 13a to 13e are respectively provided with P-side electrodes 18a to 18e, and the substrate 17 is provided with an N-side electrode 19.
Here, the circuit configuration is such that a reverse bias or a forward bias can be applied to each of the P-side electrodes 18a to 18e.

The cavity length L of the mode-locked semiconductor laser 1 is approximately c / 2nf (where c is the speed of light in vacuum and n is the refractive index including group velocity dispersion). Further, by forming the cap layers 13a to 13e separately, the regions of the cap layers 13b and 13d are saturable absorption regions 11.
a, 11b, and cap layers 13a, 13b
Regions c and 13e are configured as gain regions 12a, 12b and 12c. And, these saturable absorption regions 1
1a and 11b are at a position of L / m (where m is an integer of 2 or more) with respect to the cavity length L, here, the incident end face 2
Saturable absorption regions 11a and 11b are arranged at positions 0a to L / 2, and further at positions L / 4 from this position.

On the other hand, the input circuit 1X includes a lens 3a,
The optical pulse data train S1 which is composed of the optical isolator 4a and the lens 3b and is emitted from the optical fiber 2a is incident on the incident end face 20a of the mode-locking semiconductor laser 1.
The output circuit 1Y includes a lens 3c, an optical isolator 4b, and a lens 3d, and makes the optical clock pulse train S2 output from the emission end face 20b of the mode-locked semiconductor laser 1 incident on the optical fiber 2b.

The operation of the optical clock extraction device thus constructed will be described with reference to FIG. For example, here, for the P-side electrodes 18a to 18e of the mode-locking semiconductor laser 1,
The reverse bias is applied only to the saturable absorption region 11a, and the forward bias is applied to the gain regions 12a to 12c and the saturable absorption region 11b. As a result, the mode-locked semiconductor laser 1 performs the passive mode-locking operation with the self-modulation frequency of 2f when the optical pulse data train S1 is not input. Therefore, as shown in FIG. 2B, when the optical pulse data train S1 of the clock frequency 2f is incident on the mode-locked semiconductor laser 1 from the input circuit 1X, the optical pulse train of the frequency 2f is stably reproduced in the resonator. Supported by amplification,
The optical clock pulse train having the revolving frequency of 2f is emitted from the emitting end face 20b.
Is emitted from. Therefore, the output circuit 1Y outputs an optical clock pulse train of frequency 2f.

Similarly, a reverse bias is applied only to the saturable absorption region 11b, and a forward bias is applied to the gain regions 12a to 12c and the saturable absorption region 11a. As a result, the mode-locked semiconductor laser 1 performs the passive mode-locking operation with the self-modulation frequency of 4f when the optical pulse data train S1 is not input. Therefore, as shown in FIG. 2C, when the optical pulse data train S1 having the clock frequency 4f is incident on the mode-locked semiconductor laser 1 from the input circuit 1X, the optical pulse train having the frequency 4f is stably reproduced in the resonator. Supported by amplification, an optical clock pulse train having a circulating frequency of 4f is emitted from the emitting end face 20b. Therefore,
The output circuit 1Y outputs an optical clock pulse train of frequency 4f.

In the saturable absorption region to which a reverse bias is applied, when a high intensity light such as an incident light pulse passes, it exhibits an absorption saturation action, while a low intensity light such as spontaneous emission light is emitted. Since it exhibits an absorption effect when passing through it, the mode-locked semiconductor laser 1 can suppress spontaneous emission noise that is continuously amplified while being amplified like a normal laser even if the optical pulse goes around the resonator a number of times. it can.

On the other hand, when the frequency of the incident optical pulse data train S1 is f, the mode-locked semiconductor laser 1
In the above, the self-modulation function of the frequency f is enhanced and the self-modulation function of the mf is suppressed by the absorption saturation effect when the incident laser beam passes as described above, corresponding to the circulating frequency in the resonator. Therefore, as shown in FIG. 2A, the regenerative amplification of the optical pulse train circulating in the resonator at the frequency f is supported,
The optical clock pulse train S2 having the frequency f is emitted.

Therefore, in the optical clock extraction device of the first embodiment, even when the clock frequency of the optical pulse data train as the input light is different from f, 2f, 4f,
By changing the bias of the saturable absorption region of the mode-locked semiconductor laser 1, it is possible to output an optical clock pulse train having a clock frequency corresponding to each optical pulse data train. As a result, it becomes possible to generate and output optical clocks of different frequencies by one mode-locked semiconductor laser, in other words, one optical clock extraction device including an input circuit and an output circuit. It is possible to achieve simplification and reduce the facility cost.

Here, in the present invention, as shown in FIG. 3, in the mode-locking semiconductor laser 1A, the saturable absorption region 11c is formed by forming the cap layer 13f and the P-side electrode 18f at the position of the incident end face 20a thereof. May be attached. In this way, the optical pulse data train S having the clock frequency f
When 1 is incident, a reverse bias is applied to the saturable absorption region 11c arranged at the resonator end, and a forward bias is applied to the other saturable absorption regions 11a and 11b and the gain regions 12a to 12c. It is also possible to emit an optical clock pulse train of frequency f.

In the above embodiment, the case where m is 2 or 4 has been described, but the value of m can be set to an arbitrary value as necessary, whereby an optical clock pulse train of frequency mf can be set. It goes without saying that you can get

[0018]

As described above, according to the present invention, an optical pulse data train having a clock frequency substantially equal to the orbital frequency of the light of the mode-locked semiconductor laser or an integer multiple thereof is input, and based on this clock frequency, By changing the bias condition for the mode-locked semiconductor laser having the saturation absorption region and the gain region, it is possible to output the optical clock pulse train having the clock frequency of the optical pulse data train as the repetitive frequency. The optical clock extraction device can obtain the optical clock pulse train having the frequency f and the frequency mf that is an integral multiple of the frequency f, so that the facility of the optical communication device can be simplified and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a conceptual configuration of a first embodiment of the present invention.

FIG. 2 is a diagram showing timings of an incident light pulse data train and an emitted light clock pulse train according to the present invention.

FIG. 3 is a configuration diagram showing a conceptual configuration of a second embodiment of the present invention.

[Explanation of symbols]

 1, 1A Mode-locked semiconductor laser 1X input circuit 1Y output circuit 2a, 2b Optical fiber 3a-3d Lens 4a, 4b Optical isolator 11a-11c Saturable absorption region 12a-12c Gain region 13a-13f Cap layer 14 P-type cladding layer 15 Active layer 16 N-type clad layer 17 Substrate 18a-18f P-side electrode 19 N-side electrode 20a, 20b End surface

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H04B 10/26 10/14 10/04 10/06

Claims (5)

[Claims] 1. An optical clock extraction method in which input light is incident on a mode-locking semiconductor laser and output light corresponding to the input light is emitted from the mode-locking semiconductor laser. The optical pulse data train is inputted as an optical pulse data train having a clock frequency substantially equal to the circulating frequency of laser light or an integral multiple thereof, and the bias condition applied to the mode-locked semiconductor laser is changed based on this clock frequency, and the optical pulse data train is supplied. An optical clock extraction method which outputs an optical clock pulse train having the clock frequency of the above as a repetition frequency. 2. An optical clock extractor comprising: input means for guiding input light; a mode-locking semiconductor laser to which the input light is input; and output means for guiding output light from the mode-locking semiconductor laser to an external optical circuit. In the device, in the mode-locked semiconductor laser, a saturable absorption region is arranged at a position of 1 / m (m is an integer) of the cavity length thereof, and has a clock frequency m times the optical circulation frequency in the cavity. An optical clock extraction device, wherein a reverse bias is applied to the saturable absorption region when an optical pulse data train is incident. 3. Mode-locked semiconductor lasers have different m
When a plurality of saturable absorption regions and gain regions corresponding to the values are arranged, and an optical pulse data train of m times the clock frequency having different m values with respect to the optical circulation frequency in the resonator is incident. 3. The optical clock extraction device according to claim 2, wherein the saturable absorption region arranged at a position having the same m value is reverse biased, and the other saturable absorption region and gain region are forward biased. 4. A first saturable absorption region is arranged at a position of L / m1 with respect to a cavity length L from an incident end face of a mode-locking semiconductor laser, and L / m is provided from the first saturable absorption region.
The optical clock extraction device according to claim 3, wherein the second saturable absorption region is arranged at a position of 2 (m1 and m2 are different integers). 5. The optical clock extraction device according to claim 4, wherein the saturable absorption region is arranged at the incident end face position of the mode-locked semiconductor laser.