KR20090061100A - Multiwavelength fiber laser apparatus including coupled cavities and oscillation method of multiwavelength laser - Google Patents

Abstract

A multi-wave length laser device and an oscillation method of the multi-wave length laser are provided, which obtain single mode multi-wave length laser by suppressing oscillation of the side mode. A multi-wave length laser device comprises the combination oscillator, the semiconductor optical amplifier(130), the multi-wavelength filter(140), and the variable opto-coupler(180). The combination oscillator comprises the first resonator(110) and the connected second resonator(120). The combination oscillator reduces the optical signal of the side mode by oscillating the optical signal in the set frequency. The semiconductor optical amplifier produces the laser light signal. The multi-wavelength filter authorizes the optical signal generated by the semiconductor optical amplifier to the first resonator.

Description

MULTIWAVELENGTH FIBER LASER APPARATUS INCLUDING COUPLED CAVITIES AND OSCILLATION METHOD OF MULTIWAVELENGTH LASER}

The present invention relates to a multi-wavelength fiber laser device comprising a coupled resonator and a method of oscillating a multi-wavelength laser. In detail, the present invention filters the laser optical signal generated by the semiconductor optical amplifier into a plurality of optical signals, and oscillates the optical signal at a frequency that satisfies the resonance condition of the coupling resonator, thereby allowing the optical signal in the side mode. The present invention relates to a multi-wavelength fiber laser device and a method of oscillation of a multi-wavelength laser that reduce the power to generate a single mode multi-wavelength laser.

Recently, as the communication traffic increases due to the spread of the Internet, a wavelength division multiplexing (WDM) scheme for multiplexing a plurality of wavelengths and transmitting them through one optical fiber has been widely used. In addition, an optical time division multiplexing (OTDM) method in which an optical pulse is divided into channels and performs data modulation in advance on a fundamental repetition frequency of a pulse train before being multiplexed, and multiplexes each channel in an optical domain, is also widely used. .

Implementation of these methods requires the development and performance verification of optical equipment and optical components that meet the needs of wavelength division multiplexing systems. Accordingly, research on multi-wavelength light sources has been actively conducted, and this has been applied to optical fiber sensors and spectroscopy.

The conventional method for implementing a multi-wavelength light source is a method of multiplexing a diode laser, but this is not suitable for the purpose of measuring the performance and characteristics of an optical component because the configuration is complicated and the equipment is expensive.

On the other hand, there is a method of slicing a light source of a light emitting diode (LED) or an erbium-doped fiber amplifier (EDFA) with a comb filter, but the output intensity per channel is low and the output flatness is poor. It does not have a disadvantage in practicality.

Other technologies include femtosecond ( ^10-15 seconds) mode locked lasers, and techniques for slicing supercontinuum using optical fibers with high nonlinearity. There is a disadvantage.

The present invention for solving the above-described problems of the prior art, the output light of the laser is switched to another mode by using the Vernier effect that the optical signal is oscillated only at a frequency that simultaneously meets the resonance conditions of the plurality of resonators It is an object of the present invention to provide a multi-wavelength fiber laser device and a method of oscillating a multi-wavelength laser capable of stable single mode oscillation without mode hopping.

A multi-wavelength optical fiber laser device according to an embodiment of the present invention for achieving the above object includes a first resonator and a second resonator connected to each other, and oscillates an optical signal at a predetermined frequency to provide a side mode. A coupling resonator for reducing the optical signal; A semiconductor optical amplifier (SOA) for generating a laser optical signal; A multi-wavelength filter for filtering the optical signal generated by the semiconductor optical amplifier into a plurality of optical signals and applying the same to the first resonator; And a variable optical coupler that separates and outputs at least a portion of the optical signal from the first resonator.

An oscillation method of a multi-wavelength laser according to an embodiment of the present invention may include generating a laser light signal; Filtering the optical signal generated in the step into a plurality of optical signals; Oscillating the optical signal filtered in the step at a predetermined frequency by using a combined resonator including a plurality of resonators, thereby reducing a side mode optical signal; And separating and outputting at least a portion of the optical signal from the coupling resonator.

When using the multi-wavelength fiber laser apparatus and the oscillation method of the multi-wavelength laser according to an embodiment of the present invention, the single mode multi-wavelength laser is provided by effectively suppressing the side mode oscillation by the Vernier effect. can do. In addition, the oscillation wavelength of the multiwavelength laser oscillating can be changed by adjusting the wavelength spacing of the multiwavelength filter, and the oscillation wavelength band can be changed by adjusting the output ratio of the output optical coupler.

The multi-wavelength fiber laser generated according to an embodiment of the present invention is an economical broadcast light source or wavelength stabilization technology for wavelength locking in a wavelength division multiplexing-passive optical network (WDM-PON). Can be used as a light source. It can also be used as a light source for optical fiber sensors, optical device testing and spectroscopy.

Hereinafter, with reference to the accompanying drawings looks at in detail with respect to the preferred embodiment of the present invention.

1 is a block diagram showing the configuration of a multi-wavelength fiber laser device according to an embodiment of the present invention. Referring to FIG. 1, a multi-wavelength optical fiber laser device according to the embodiment includes a semiconductor optical amplifier (SOA) 130, a multi-wavelength filter 140, and first and second resonators 110 and 120. It comprises a coupling resonator and a variable optical coupler 180 including a.

The combined resonator is a resonator configured by connecting a plurality of resonators. In the exemplary embodiment illustrated in FIG. 1, the combined resonator includes a first resonator 110, a second resonator 120, and an optical fiber coupler 170. Both the first resonator 110 as the main resonator and the second resonator 120 as the negative resonator are annular, and the optical fiber coupler 170 connects the two resonators. The optical signal oscillates at a predetermined frequency while rounding the inside of the first and second resonators 110 and 120.

The semiconductor optical amplifier 130 is connected to the power supply 135 and converts the supplied electrical energy into laser light to generate a laser light signal. The laser optical signal generated by the semiconductor optical amplifier 130 has a wideband output spectrum in which the signal appears over a predetermined band. The generated optical signal is applied to the annular first resonator 110.

Since the optical signal generated by the semiconductor optical amplifier 130 is circulated through the coupling resonators 110 and 120, the semiconductor optical amplifier 130 is a transmission type optical amplifier that can transmit the optical signal in the embodiment shown in FIG. It is composed. In addition, in one embodiment of the present invention, the semiconductor optical amplifier 130 may be composed of an Erbium-Doped Fiber Amplifier (EDFA).

The multi-wavelength filter 140 is connected to the first resonator 110 and receives the optical signal of the broadband spectrum generated by the semiconductor optical amplifier 130. The multi-wavelength filter 140 filters the optical signal passing therethrough into a plurality of optical signals located at periodic frequency intervals. For example, the multi-wavelength filter 140 may use an interleaver, a Fabry-Perot filter, or an arrayed waveguide grating (AWG) having periodic transmission characteristics in the frequency domain. The optical signal is filtered by the multi-wavelength filter 140 into a plurality of optical signals, thereby enabling multi-wavelength oscillation of the laser optical signal.

In one embodiment of the present invention, an optical isolator 150 may be used in combination with the first resonator 110 to suppress the reverse travel of the optical signal in the coupling resonators 110 and 120. In this case, the optical isolator 150 serves to improve the oscillation efficiency by suppressing the reverse direction of the optical signal due to reflection in the first resonator 110.

In the embodiment shown in FIG. 1, the optical isolator 150 is located adjacent to the multiwavelength filter 140. However, this is exemplary, and the optical isolator 150 is the same even if disposed at any position in the resonator through which the optical signal is circulated. Actions and effects can be exhibited and are included within the scope of the spirit of the invention.

The optical signal passing through the multi-wavelength filter 140 and the optical isolator 150 is oscillated by the coupling resonators 110 and 120 including the first resonator 110, the second resonator 120, and the optical coupler 170. do. In the embodiment shown in FIG. 1, the combined resonator includes two resonators of the first and second resonators 110 and 120. However, this is exemplary and the number of resonators included in the coupled resonator may be any number of two or more.

The optocoupler 170 of the coupling resonator is a device for coupling the first resonator and the second resonator. In the optical coupler 170, a part of the optical signal is coupled to the second resonator 120, and part of the optical signal continues to the first resonator 110. In this case, the resonance conditions of both resonators are satisfied due to the Vernier effect. The oscillation will only occur at frequencies. In one embodiment of the invention, the optical coupler 170 may branch the optical signal to both resonators in a ratio of 50:50.

In the coupled resonator, the lengths of the first resonator 110 and the second resonator 120 are respectively L _1. And L ₂ , the phase condition of the resonance mode that satisfies the resonance condition of each resonator is represented by Equations 1 and 2 below.

βL ₁ = 2k ₁ π

βL ₂ = 2k ₂ π

In Equations 1 and 2, β is a propagation constant in each resonator and k ₁ and k ₂ Is a positive integer.

Here, the free spectral ranges (FSRs) of the first resonator 110 and the second resonator 120 are assumed to be FSR ₁ and FSR ₂ , respectively. At this time, due to the vernier effect, the free spectrum range in the entire coupling resonator has a minimum common multiple of FSR ₁ and FSR ₂ . Therefore, the side mode suppression ratio is determined according to the length of each resonator, and a multi-mode fiber laser of a single mode can be obtained.

In the present specification, the mode is a term used to indicate an energy distribution of a laser light signal. Single mode means a case in which one peak in an optical signal of an arbitrary channel, and multi mode means that an arbitrary channel optical signal is generated by a plurality of side peaks in addition to the main peak. It means the case. In this case, the optical signal of the side mode means optical signals of a portion corresponding to the side peak in addition to the main peak.

In addition, in one embodiment of the present invention, polarization regulators 160 and 165 may be connected to and used in the respective resonators 110 and 120 of the coupling resonator. The polarization controllers 160 and 165 adjust the polarization of the optical fiber in each resonator to minimize the size of the side mode optical signal in the multi-wavelength fiber laser device. Minimizing side mode signals using polarization regulators 160 and 165 allows for more stable single mode multi-wavelength laser oscillation.

The single mode multi-wavelength optical signal generated while passing through the coupling resonator and the polarization regulators 160 and 165 is input to the variable optical coupler 180 for outputting the optical signal. The variable optical fiber coupler 180 separates and outputs a signal having a predetermined ratio among the input optical signals from the coupling resonator, and circulates the remaining optical signals in the first resonator 110 again.

In one embodiment of the present invention, it is also possible to adjust the oscillation wavelength band of the multi-wavelength fiber laser device to a desired band by adjusting the output ratio of the variable optical coupler 180. For example, when the ratio of inputting the coupled resonator to the coupling resonator without outputting the optical signal from the variable optical coupler 180 is defined as a feedback ratio, the wavelength of the optical signal output from the multi-wavelength fiber laser device increases as the feedback ratio is increased. do.

2 is a block diagram showing the configuration of a multi-wavelength fiber laser device according to another embodiment of the present invention. Referring to FIG. 2, the multi-wavelength fiber laser device according to the embodiment includes a semiconductor optical amplifier 230, a multi-wavelength filter 240, a combined resonator including a third and fourth resonators 220 and 225, and variable light. And a coupler 270 and a resonator mirror 21.

In the embodiment shown in FIG. 2, the coupled resonator comprises a first resonator 220, a second resonator 225, and an optocoupler 260. The functions of the respective resonators 220 and 225 and the optocoupler 260 are the same as those described above with reference to FIG. 1, but in the embodiment shown in FIG. 2, the first resonator 220, which is the main resonator of the coupled resonator, The difference is that it is straight.

The laser optical signal generated by the semiconductor optical amplifier 230 passes through the first resonator 220, which is a linear resonator, is reflected back from the resonator mirror 210, and circulates in the first resonator 220. That is, the optical signal is gained by round-trip between the semiconductor optical amplifier 230 and the resonator mirror 210 positioned at both ends of the first resonator 220. In this case, the semiconductor optical amplifier 230 may be configured as a reflective semiconductor optical amplifier (RSOA) to circulate the optical signal. In addition, the resonator mirror 210 may be formed by attaching a mirror using a single-side coating of a fiber or a micro optic.

Specific operations and functions of the semiconductor optical amplifier 230, the multi-wavelength filter 240, and the variable optical coupler 270 are the same as those described above with reference to FIG. 1, and thus can be easily understood by those skilled in the art. The detailed description may be omitted.

3 is a flow chart showing each step of the oscillation method of a multi-wavelength laser according to an embodiment of the present invention. Hereinafter, a method of oscillating a multi-wavelength laser according to the embodiment shown in FIG. 3 will be described with reference to the multi-wavelength laser device according to the embodiment shown in FIG. 1 for convenience of description.

The oscillation method of the multi-wavelength laser according to the above embodiment starts with generating the laser optical signal by the electric energy supplied to the semiconductor optical amplifier 130 (S2). The generated optical signal is a wideband signal over a predetermined wavelength band, and the multi-wavelength filter 140 filters it into a plurality of optical signals according to frequencies (S2). For example, the multi-wavelength filter 140 filters the optical signal generated by the semiconductor optical amplifier 130 into a plurality of optical signals having periodic wavelength intervals.

In an embodiment of the present invention, when the main resonator 110 of the coupling resonator is annular as shown in FIG. 1, the optical isolator 150 may further suppress the reverse process of the optical signal. It may also be (S3).

The multi-wavelength optical signal filtered by the multi-wavelength filter 140 is oscillated at a predetermined frequency by a coupling resonator including the first resonator 110 and the second resonator 120 (S4). The oscillation frequency is a frequency that satisfies both resonance conditions of the first and second resonators 110 and 120. In this case, due to the Vernier effect, the free spectral range of the coupled resonator becomes a common multiple of the free spectral range of the first resonator 110 and the free spectral range of the second resonator 120. Therefore, the optical signal of the side mode which does not correspond to this is suppressed, and it oscillates by a single mode multi-wavelength optical signal.

In an embodiment of the present invention, polarization regulators 160 and 165 are attached to the first and second resonators 110 and 120, respectively, to adjust polarization of the optical fiber in each resonator to minimize the intensity of the side mode optical signal. It may be further performed (S5).

Next, the variable optical coupler 180 for outputting the optical signal outputs the optical signal separated from the coupling resonator by a predetermined ratio (S6). In one embodiment of the present invention, it is also possible to adjust the wavelength ratio of the output optical signal to the desired band by adjusting the output ratio of the variable optical coupler 180. For example, as the output ratio of the variable optical coupler 180 decreases, the wavelength band of the output optical signal moves toward the longer wavelength.

4 is a graph illustrating an output waveform of a multi-wavelength fiber laser device according to an embodiment of the present invention. In the multi-wavelength fiber laser device according to the above embodiment, the multi-wavelength filter uses a 50/100 GHz interleaver having a 100 GHz interval, and the variable optical coupler for output has an output ratio of 10%, and the main resonator and the sub-resonator of the coupled resonator are The resonators are 15 m and 0.5 m long, respectively. The semiconductor optical amplifier has a length of 1 mm and a double-sided reflectance of 0.01%, with a fiber-to-fiber gain of about 21 dB and a saturation output of about 10 dBm at a supply current of 200 mA.

Referring to FIG. 4, by a multi-wavelength fiber laser device according to an embodiment of the present invention, a multi-wavelength having a similar power with a frequency interval of 100 GHz (wavelength interval of 0.8 nm) in a wavelength band of 1565 nm to 1585 nm. An optical fiber laser light signal was output. At this time, the side mode suppression ratio (SMSR) is about 40 dB and the line width of each light is 0.1 nm or less. On the other hand, according to another embodiment of the present invention, a multi-wavelength laser having more wavelengths can be obtained when using the Fabret-Parrot filter spaced 50 GHz or 25 GHz as a multi-wavelength filter.

5 is a graph exemplarily illustrating a spectrum of an output optical signal according to a change in a feedback ratio of a variable optical coupler in a multi-wavelength fiber laser apparatus according to an exemplary embodiment of the present invention. Each graph (1, 2, 3, 4, 5, 6) shows the spectrum of the output optical signal when the feedback ratio is 5%, 10%, 20%, 50%, 80% and 90%, respectively. As shown, it can be seen that as the feedback ratio increases, that is, as the output ratio decreases, the oscillation wavelength band of the output optical signal moves toward the longer wavelength. This is due to a band filling effect in which the peak of the gain curve moves to a shorter wavelength as the carrier density inside the semiconductor increases. Therefore, the oscillation wavelength band can be adjusted to a desired wavelength band by adjusting the output ratio of the variable optical coupler.

6A and 6B illustrate a signal of any one wavelength channel of a conventional multi-wavelength fiber laser device and an output optical signal of a multi-wavelength fiber laser device according to an embodiment of the present invention with a photo detector and an RF spectrum analyzer. A graph showing the RF spectrum. 6A and 6B both show the spectrum of the optical signal in the side mode portion.

6A shows an output waveform of a conventional multi-wavelength fiber laser device. Referring to FIG. 6A, a plurality of vertical modes oscillate in a conventional multi-wavelength fiber laser. On the other hand, Figure 6b shows the output waveform of the multi-wavelength fiber laser device according to an embodiment of the present invention. Referring to FIG. 6B, in the multi-wavelength fiber laser device according to the embodiment, oscillation occurs only at frequencies simultaneously satisfying the resonance conditions of the plurality of resonators due to the vernier effect, thereby greatly reducing the side mode.

When the multi-wavelength fiber laser device and the oscillation method of the multi-wavelength laser according to an embodiment of the present invention described above are used, the single-mode multi-wavelength is effectively suppressed by the side mode oscillation by the Vernier effect. A laser can be provided. In addition, the wavelength spacing of the multi-wavelength laser can be changed by adjusting the wavelength spacing of the multi-wavelength filter, and the oscillation wavelength band can be changed by adjusting the output ratio of the output optical coupler.

The multi-wavelength fiber laser generated according to an embodiment of the present invention is an economical broadcast light source or wavelength stabilization technology for wavelength locking in a wavelength division multiplexing-passive optical network (WDM-PON). Can be used as a light source. It can also be used as a light source for optical fiber sensors, optical device testing and spectroscopy.

While specific embodiments of the present invention have been illustrated and described, the technical spirit of the present invention is not limited to the accompanying drawings and the above description, and various modifications can be made without departing from the spirit of the present invention. It will be apparent to those skilled in the art, and variations of this form will be regarded as belonging to the claims of the present invention without departing from the spirit of the present invention.

1 is a block diagram showing a multi-wavelength optical fiber laser device according to an embodiment of the present invention.

2 is a block diagram showing a multi-wavelength optical fiber laser device according to another embodiment of the present invention.

3 is a flow chart showing each step of the oscillation method of a multi-wavelength laser according to an embodiment of the present invention.

4 is a graph illustrating an output waveform of a multi-wavelength fiber laser device according to an embodiment of the present invention.

5 is a graph exemplarily illustrating a change in a wavelength band of an output optical signal according to a change in an output ratio of a variable optical coupler in a multi-wavelength optical fiber laser apparatus according to an embodiment of the present invention.

6A and 6B are exemplary graphs showing the output optical signal of the conventional multi-wavelength fiber laser device compared with the output optical signal of the multi-wavelength fiber laser device according to an embodiment of the present invention.

Claims (15)

A combined resonator including a first resonator and a second resonator connected to each other, and oscillating an optical signal at a predetermined frequency to reduce an optical signal in a side mode; A semiconductor optical amplifier (SOA) for generating a laser optical signal; A multi-wavelength filter for filtering the optical signal generated by the semiconductor optical amplifier into a plurality of optical signals and applying the same to the first resonator; And And a variable optical coupler for separating and outputting at least a portion of the optical signal from the first resonator. The method of claim 1, The multi-wavelength filter, Multi-wavelength fiber laser device, characterized in that the interleaver (Interleaver) or Fabry-Perot filter (Fabry-Perot filter). The method of claim 1, The preset frequency is a multi-wavelength fiber laser device, characterized in that the frequency satisfying the resonance conditions of the first resonator and the second resonator. The method of claim 1, And a polarization controller connected to each of the first resonator and the second resonator to adjust polarization of the first resonator and the second resonator so as to minimize side mode optical signals. . The method of claim 1, And the first resonator is a ring-shaped resonator. The method of claim 5, And an optical isolator connected to the first resonator to suppress backward movement of the optical signal. The method of claim 1, The first resonator is a linear resonator, The semiconductor optical amplifier is a reflective semiconductor optical amplifier (RSOA) connected to one end of the first resonator, And a resonator mirror connected to the other end of the first resonator to reflect an optical signal. The method of claim 1, The multi-wavelength fiber laser device, And outputting an optical signal having a different wavelength band according to the output ratio of the variable optical coupler. The method of claim 1, And the plurality of optical signals have different wavelength bands. Generating a laser light signal; Filtering the optical signal generated in the step into a plurality of optical signals; Oscillating the optical signal filtered in the step at a predetermined frequency by using a combined resonator including a plurality of resonators, thereby reducing a side mode optical signal; And And separating and outputting at least a portion of the optical signal from the coupling resonator. The method of claim 10, And the predetermined frequency is a frequency satisfying a resonance condition of the plurality of resonators. The method of claim 10, Reducing the optical signal of the side mode, And controlling the polarizations of the plurality of resonators so as to minimize the optical signals in the side mode. The method of claim 10, And suppressing the reverse direction of the optical signal in the coupling resonator. The method of claim 10, Separating and outputting at least a portion of the optical signal from the coupling resonator, And a step of outputting an optical signal having a different wavelength band according to the ratio of the optical signals to be output. The method of claim 10, And the plurality of optical signals have different wavelength bands from each other.

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