JPS60426A - Superhigh-speed optical phase modulating system - Google Patents

Abstract

PURPOSE:To execute an optical phase modulation at a superhigh speed, and to improve an upper band width and an S/N ratio by using a frequency high-stable and high-Q laser obtained by a fact that a laser diode is not modulated directly, as a carrier wave, and executing the phase modulation on an optical fiber. CONSTITUTION:A narrow band filter 5 reflects only an oscillation center frequency f0 part of a laser diode (LD)6, and transmits or scatters a part shifted from f0. Light absorbing bodies 4 absorb unnecessary light which has transmitted through the narrow band filter 5. By placing them in order of the light absorbing bodies 4, the narrow band filter 5, the LD6, and an optical fiber 7 for fetching light, it becomes a frequency high-stable, high-Q, single polarized wave and single mode light source which is capable of obtaining output light, for instance, whose spectrum width is one angstrom. By using this light source, an optical phase modulation by which the band width and S/N are extremely large can be executed at a superhigh speed with high stability.

Description

[Detailed Description of the Invention] (a) Technical Field of the Invention The present invention relates to an optical phase modulation method, which is capable of ultra-high speed optical phase modulation using the mutual nonlinear effect (Kerr effect) of optical cores, and is highly stable. This paper relates to an ultrahigh-speed optical phase modulation system that can achieve extremely large bandwidths.

(b) Conventional technology and problems As a phase modulation method for light, conventionally, optical ultrasonic phase modulation (A
There is a PZT method that performs phase modulation by applying a voltage to a piezoelectric ceramic and causing it to vibrate, but since both use a low Q laser that is easy to modulate, the speed is several hundred.
The voltage is on the order of MHz, the voltage to be handled is high, the size is large, and the stability is not fully satisfactory. In addition, the method of directly phase modulating the laser diode (LD) requires a low Q, so there are problems with noise such as phase modulation and amplitude modulation, and the modulated wave changes the temperature of the LD and changes the frequency, causing the frequency to change. The conventional optical phase modulation method has the above-mentioned drawbacks.

(c) Purpose of the Invention In view of the above-mentioned drawbacks, the purpose of the present invention is to perform ultra-high speed optical phase modulation using the Kerr effect of an optical fiber, and to achieve ultra-high speed optical phase modulation that is highly stable and has a large S/N in the band. The purpose of the present invention is to provide a velocity optical phase modulation method.

(d) Structure of the Invention In order to achieve the above object, the present invention combines and injects a carrier wave into a single-mode polarization-maintaining optical fiber from an ultra-high frequency stable, high Ql-polarized, single-mode light source. Also, polarized single mode light is coupled and input as a phase modulation signal from an ultra high speed, low Q, optical amplitude modulation light source, and ultra high speed optical phase modulation is performed by the Kerr effect of the optical fiber. In other words, by using a high-frequency, stable, and high-Q laser as a carrier wave, which is possible only by not directly modulating the LD, and performing phase modulation on an optical fiber, ultra-high-speed optical phase modulation is achieved with high stability, and the band and signal N are extremely low. (e) Embodiments of the invention Examples of the invention will be described below with reference to the drawings.

Figure 1 is an explanatory diagram of the principle of the present invention, and Figure 2 is an ultra-high frequency stable, high-Q, single-polarization, single-mode light source used in the present invention.
Figure 3 is a block diagram of an example of an ultra-high-speed, low-Q, optical amplitude modulation light source (hereinafter referred to as low-QLD) used in the present invention.
LD) is shown in a side sectional view.

In the figure, 1 is high QLD, 2 is low QLD, and 3.7.10 is single mode polarization maintaining optical fiber (hereinafter referred to as optical fiber).
, 4 is a light absorber, and 5 is a narrow band reflection filter.

6 is a laser diode (hereinafter referred to as LD), 8 is a metal bar for bias supply, and 9 is a radial fixture.

11 is a termination short circuit board, 12 is an optical matching device, and 13 is an LD.

14 indicates a waveguide.

The center optical frequency of high QLDI and low QLD2 is ω.

ω, then the coupling length L between the high QLDI optical carrier and the low QLD2 optical modulation wave on the optical fiber 3 is t
ocl-=1-.

ω −ω Δω Further, the optical phase constant β is expressed by the following equation.

However, y - impedance of the optical fiber 3 + = Kerr effect constant, PM (t) = optical modulation wave light intensity, 1 = time.

Therefore, the optical phase modulated wave f(1) is expressed by the following equation, f (
t)=A Co5(Gll 1β(,t) −11
--- (2) Optical phase modulation is performed on the optical fiber 3. Here, as the high QLDI, for example, one as described next using FIG. 2 is used.

The single mode laser shown in FIG. 2 was developed by the applicant in 1957.
The patent application was filed on May 28th, 1987-168969, and the narrowband filter 5 is a filter that reflects only the spectrum of the center frequency fo of the oscillation optical frequency of the LD 6, and is a filter that deviates from the center frequency fo. The light absorber 4 absorbs unnecessary light that has passed through the narrow band filter 5. As shown in FIG. 2, the light absorber 4. Narrowband filter5. LD6. By arranging the optical fibers 7 in the order in which the light is extracted, a high frequency stable and high Q-
It is a highly polarized, single mode light source.

Further, as the low QLD2, for example, one as described below with reference to FIG. 3 is used.

The modulator using the LD shown in FIG.
The patent application was filed in Japanese Patent Application No. 55-075426 on June 6, 2007, and the LD 13 is located at the center of the waveguide 14 and in front of the terminal shorting plate 11, and is designed to detect one of the modulated waves input from the waveguide 14.
/4 wavelength, one end of the metal rod 8 for bias supply extends so as to contact the LD 13, and the other end of the metal rod 8 is pulled out from the outside of the waveguide 14. The metal rod 8 that has been pulled out is surrounded by a radial filter 9 that prevents high-frequency shallow grooves, and an optical matching device 12 is arranged opposite the LD 13, and an optical fiber that transmits the optical output from the optical matching device 12 is provided. 10 is arranged, and when a modulated wave having a frequency from several GHz to about 30 GHz is input to the waveguide 14, an amplitude-modulated optical output is obtained in the optical fiber 10. A single light source with optical amplitude modulation
It is designed to output 9-wave sheep-mode light.

Using light with a wavelength of, for example, 1.5 μm from a high QLDI as described above, and light with a wavelength of, for example, 0.78 μm from a low QLD2,
By performing phase modulation on the optical fiber 3 without directly modulating the LD, highly stable and ultra-high speed phase modulation is possible, and the carrier wave is ultra-high frequency stable, high-Q light from the LD, and the modulated wave is also ultra-high. Since the light is from a high speed, low Q, optical amplitude modulated light source, the S/N can be increased even in the band.

The high QLDI and low QLD2 may be coupled into the optical fiber 3 using an optical method, or an optical directional coupler 15 as shown in FIG. 4 may be used.

Also, if the output of high QLDI is small, the output of high QLDI is connected to the injection locked LD as shown in Figure 5.
16 may be injected and amplified and its output may be used as a carrier wave.

It is also possible to use two sets of high QLDI and low QLD2, and to polarize the output lights of these two sets with their planes of polarization shifted by 90 degrees.

If the polarization plane of the output light of one high QLD is shifted by 45 degrees, this one high QLD will be shifted by 90 degrees (f).Effects of the InventionAs explained in detail above, according to the present invention, It is high speed and highly stable, and has the effect of enabling optical phase modulation that can be made extremely wide across 11 bands.

[Brief explanation of the drawing]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a configuration diagram of an example of an ultra-high frequency stable, high Q, single polarization, single mode light source used in the present invention, and Fig. 3 is a diagram illustrating the principle of the present invention. A side sectional view of the ultra-high speed, low Q, optical amplitude modulation light source to be used, FIG. 4 is a block diagram when coupling using the optical directional coupler of the embodiment of the present invention,
FIG. 5 is a block diagram when amplifying carrier wave light. In the figure, 1 is an ultra-high frequency stable, high-Q, single-polarization, single-mode light source, 2 is an ultra-high-speed, low-Q, optical amplitude modulation light source, 3, 7.
10 is a single mode polarization maintaining optical fiber. 4 is a light absorber, 5 is a narrowband reflection filter, 6.13 is a laser diode, and 8 is a metal rod for bias supply. 9 is a radial filter, 11 is a termination short-circuit plate, 12 is an optical matching device, 14 is a waveguide, 15 is an optical directional coupler, 16
shows an Injiexi four-lock laser diode. Figure 1/ (Figure 2 123 Figure 3) Figure 4

Claims (1)

[Claims] Ridge-mode fine wave preservation light 7 AINO (with ultra-high frequency stability and
A high-Q, single-polarized, single-mode light source is coupled as a carrier wave, and an ultra-high-speed, low-Q, optical amplitude modulation light source is coupled as a phase-modulated signal. An ultra-high speed optical phase modulation method characterized by phase modulation on the optical fiber.