CN101295853A - A Wavelength Tunable External Injection Gain Switched Laser - Google Patents

Abstract

The invention relates to a gain switch laser, in particular to a wavelength tunable external injection gain switch laser. The invention comprises a gain switch laser body, an optical fiber amplifier, a narrow-band tunable filter, a first coupler, and a second coupler; the first coupler, the optical fiber amplifier, the narrow-band tunable filter and the second coupler are sequentially connected in series through an optical fiber At the signal output end of the gain switch laser body, the second coupler is connected to the first coupler through the output fiber. In order to solve the technical problems of the gain switch laser in the background technology, the present invention provides a wavelength tunable external injection gain switch laser with tunable, wide application range, simple structure, small volume, low cost and pure spectrum.

Description

A Wavelength Tunable External Injection Gain Switched Laser

technical field

The invention relates to a gain switch laser, in particular to a wavelength tunable external injection gain switch laser.

Background technique

The ultra-short optical pulse source is one of the core components to realize ultra-high-speed and large-capacity all-optical communication systems and networks. It also has important application value in ultra-broadband optical signal sampling, optical storage, and ultra-high-speed photonic analog-to-digital conversion. . In practical applications, the ultrashort optical pulse source is required to have the characteristics of small size, simple structure, high repetition rate, low jitter, good versatility, low cost and high reliability. In telecommunication applications, in order to realize ultra-high-speed optical transmitters and their arrays that are compact in structure and can be mass-produced, it is also required that the ultra-short optical pulse source can be integrated with other optical devices.

Gain switching of semiconductor lasers is a simple and reliable ultrashort optical pulse technology, which can be easily applied to existing commercial semiconductor lasers, and can flexibly output picosecond-level optical pulse signals with variable repetition rates to adapt to different Communication interface rate or network upgrade, ultra-fast sampling and waveform monitoring for signals with different data rates. Although the gain-switched laser has the problems of large timing jitter and frequency chirp, it can be solved by optical injection locking and optical filtering.

The optical injection locking methods of gain-switched lasers can be divided into two methods: external injection and self-injection. Although the use of external injection and self-injection methods can solve the problem of wavelength tunability and jitter suppression of the optical pulse signal of the gain switch, the self-injection method requires the length L of the external cavity loop of the gain-switched laser and the generated ultrashort optical pulse period The repetition frequency f _r of the sequence strictly satisfies the relationship of formula ①:

$f_r=\frac{m}{\mathrm{\τ}}$ ①

Where m is a positive integer, and τ is the transmission time required for an ultrashort optical pulse signal to pass through the external cavity loop. If the transmission rate of the optical pulse signal in the external cavity loop is v, then $\mathrm{\τ}=\frac{L}{v}.$ After the design of the external cavity loop is completed, the length L of the external cavity loop is fixed, and the repetition frequency f _r of the ultrashort optical pulse cycle sequence generated by the self-injection gain switch laser can be determined by the formula ①, and the gain switch loses The characteristics of the repetition frequency f _r of the optical pulse signal can be changed flexibly. In practical applications, due to the influence of environmental temperature changes, it is difficult in engineering to ensure that the interface data rate of communication systems and networks is always the repetition frequency f _r determined by formula ①, which limits the application range of self-injection gain-switched lasers. limit. Although the external injection method can solve this problem, the external injection gain-switched laser usually needs to use an additional wavelength-tunable narrow-spectrum linewidth continuous wave (CW) light source as the seed light source for external injection, which will result in the cost of the gain-switched laser Increased, complex structure and increased volume.

Contents of the invention

In order to solve the technical problems of the gain switch laser in the background technology, the present invention provides a wavelength tunable external injection gain switch laser with tunable, wide application range, simple structure, small volume, low cost and pure spectrum.

The technical solution of the present invention is: the present invention is a wavelength-tunable external injection gain-switched laser, including a gain-switched laser body, and its special feature is that the laser also includes a fiber amplifier, a narrow-band tunable filter, and A coupler, a second coupler; the first coupler, fiber amplifier, narrow-band tunable filter and the second coupler are connected in series to the signal output end of the gain switch laser body through an optical fiber, and the second coupler is connected through an output fiber into the first coupler.

The above-mentioned gain-switched laser body is a gain-switched laser composed of an F-P semiconductor laser, a radio frequency signal generator, a radio frequency signal amplifier and a DC bias power supply.

The optical fiber amplifier mentioned above is an erbium-doped optical fiber amplifier or a semiconductor optical fiber amplifier, as well as other solid-state optical amplifiers that can cover required bands.

The above-mentioned narrow-band tunable filter can also be tunable fiber grating and other tunable narrow-band spectral component selectors.

The above-mentioned first coupler and the second coupler are both fiber couplers or beam splitters and other beam splitting devices.

On the basis of the existing gain switch laser, the present invention adds a fiber amplifier, a narrow-band tunable filter, a first coupler, and a second coupler, and the optical signal is amplified through the fiber amplifier. Tunable filter to filter narrow spectral line light components in the spontaneous emission ASE noise frequency band. The optical signal feedback loop is formed by the first coupler and the second coupler, so that the narrow-band tunable filter outputs a spectral component signal corresponding to a certain longitudinal mode of the gain switch laser body, and a small part of the signal is passed through the second coupler When injected into the gain-switched laser body, the longitudinal mode oscillation in the cavity of the gain-switched laser body corresponding to the wavelength of the injected optical signal is enhanced, changing the output wavelength value of the narrow-band tunable filter, and each time corresponds to each difference of the gain-switched laser body longitudinal mode, the central wavelength of the single longitudinal mode in the cavity of the gain-switched laser body changes accordingly, thereby realizing the tunable wavelength of the gain-switched laser. Partial output, other longitudinal modes that are not completely suppressed are filtered out, and the output spectrum is very pure, so the present invention has the following advantages:

1. The structure is simple, easy to manufacture, and can be optically integrated.

2. The present invention not only retains the characteristic that the gain switch can flexibly change the optical pulse repetition frequency, but also does not need a wavelength-tunable narrow-spectrum continuous laser as a special external injection seed light source to realize the wavelength-tunable function, which not only simplifies the System structure, and reduce system cost and volume.

3. The output spectrum is pure and single longitudinal mode, the timing jitter and frequency chirp are small, and the stability is good.

Description of drawings

Fig. 1 is a block diagram of the present invention;

Fig. 2 is the spectrogram that the present invention outputs under the light injection locking that wavelength is 1541nm;

Fig. 3 is a combined diagram of the output spectrograms of the present invention under different light injection locking;

Fig. 4 is the ultrashort optical pulse sequence when the repetition frequency of the present invention is 1 GHz;

Fig. 5 is an ultrashort optical pulse sequence of the present invention when the repetition frequency is 2.5 GHz.

Detailed ways

Referring to Fig. 1, the present invention comprises gain switch laser main body 1, fiber amplifier 7, narrowband tunable filter 8, first coupler 6 and second coupler 9; First coupler 6, fiber amplifier 7, narrowband tunable filter The first coupler 8 and the second coupler 9 are sequentially connected in series to the signal output end of the gain switch laser body 1 through an optical fiber, and the second coupler 9 is connected to the first coupler 6 through an output optical fiber.

The gain switch laser body 1 can adopt the existing gain switch laser, such as adopting the existing F-P semiconductor laser (Fabry-Perot semiconductor laser) 4, radio frequency signal generator 2, radio frequency signal amplifier 3 and DC bias power supply 5 composed of gain-switched lasers. Since the power of the optical pulse signal output by the gain-switched laser is generally low, in practical applications, an optical amplifier is usually used to enhance its power.

The optical fiber amplifier 7 can be an erbium-doped optical fiber amplifier or a semiconductor optical fiber amplifier, and other solid-state optical amplifiers that can cover the required band. It is better to use erbium-doped fiber amplifier. An ultrashort optical pulse sequence signal with multi-longitudinal-mode spectral characteristics is output from the gain-switched laser body, which is input into the optical fiber amplifier 7 for optical signal amplification.

The narrowband tunable filter 8 can also be tunable fiber grating and other tunable narrowband spectral component selectors. Since the fiber amplifier 7 will generate wide-spectrum amplified spontaneous emission (ASE) noise, the narrow-spectrum optical component located in the frequency band of the spontaneous emission ASE noise can be screened through the narrow-band tunable filter 8 arranged at the output end of the fiber amplifier 7 . In order to lock the externally injected optical signal, adjust the narrow-band tunable filter 8, the center wavelength of the selected narrow-spectrum component signal is the same as one of the longitudinal modes of the gain switch laser body 1, then the light output by the narrow-band tunable filter 8 The signal can be used as an external seed light to inject back into the gain switch laser body 1, so that the oscillation of the selected longitudinal mode in the gain switch laser body 1 cavity is obviously strengthened, and at the same time, other longitudinal modes in the gain switch laser body 1 cavity are suppressed. Therefore, the single longitudinal mode operation of the gain-switched laser body 1 is ensured, and timing jitter is effectively suppressed.

Both the first coupler 6 and the second coupler 9 are fiber couplers or beam splitters and other beam splitting devices. The first coupler 6 and the second coupler 9 form an optical signal feedback loop. Since the gain spectral line of the spontaneous emission of the fiber amplifier 7 is very wide, when the narrowband tunable filter 8 outputs a certain longitudinal mode corresponding to the gain switch laser body 1 When the spectral component signal of the signal is injected into the gain-switched laser body 1 through the second coupler 9 through the optical signal feedback loop, the longitudinal mode corresponding to the wavelength of the injected optical signal in the cavity of the gain-switched laser body 1 Increased shock. Change the output wavelength value of the narrowband tunable filter 8, and each time corresponds to each different longitudinal mode of the gain switch laser body 1, then the central wavelength of the single longitudinal mode operation in the cavity of the gain switch laser body 1 changes accordingly, thereby The tunable wavelength of the gain switch laser body 1 is realized. At the same time, when the gain switch laser body 1 is output from the narrow-band adjustable filter 8, a small part of the signal is injected back into the gain switch laser body 1, and most of the output filters out other longitudinal modes that are not completely suppressed, and the output spectrum It is very pure, which solves the phenomenon of spectral impurity after general external injection, and is of great benefit to signal transmission and amplification.

2 and 3, after adopting the novel external injection method of the present invention, the narrow-band tunable filter 8 screens out the spectral component signal corresponding to a certain longitudinal mode of the gain switch laser body 1, and injects it through the optical signal feedback loop To the F-P semiconductor laser 4 in the gain switch laser body 1, realize the single longitudinal mode operation state of the gain switch laser body 1, change the output wavelength value of the spectral component signal selector, and make it correspond to the gain switch laser body 1 every time The wavelength can be tunable, and at the same time, the frequency chirp of the gain-switched optical pulse signal is also reduced.

Referring to Fig. 4 and Fig. 5, it shows the change of the repetition frequency of the output optical pulse signal as the repetition frequency of the input radio frequency sine signal or cosine signal changes according to the experimental measurement. The gain switch laser of the invention can realize variable repetition frequency, low jitter and single longitudinal mode operation.

Claims (5)

1. A wavelength tunable external injection gain switch laser, comprising a gain switch laser body, characterized in that: the laser also includes a fiber amplifier, a narrowband tunable filter, a first coupler, and a second coupler; The first coupler, the fiber amplifier, the narrow-band tunable filter and the second coupler are sequentially connected in series to the signal output end of the gain switch laser body through an optical fiber, and the second coupler is connected to the first coupler through an output optical fiber. 2. The wavelength tunable external injection gain switch laser according to claim 1, characterized in that: the gain switch laser body is composed of an F-P semiconductor laser, a radio frequency signal generator, a radio frequency signal amplifier and a DC bias power supply Gain-switched lasers. 3. The wavelength tunable external injection gain switch laser according to claim 1 or 2, characterized in that the optical fiber amplifier is an erbium-doped optical fiber amplifier or a semiconductor optical fiber amplifier. 4. The wavelength tunable external injection gain switch laser according to claim 3, wherein the narrowband tunable filter adopts a tunable fiber grating or a tunable narrowband spectral component selector. 5. The wavelength tunable external injection gain switch laser according to claim 4, characterized in that: both the first coupler and the second coupler are fiber couplers or beam splitters.

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