introduction

Reed relay is an electronic control device, which is usually used in automatic control circuit. It is a relay that opens, closes or converts lines by the action of a tongue spring sealed in a tube with the dual action of a contact spring and an armature magnetic circuit. The wet spring relay is a tongue spring relay which seals the tongue spring and the contact in the tube and makes the mercury film wet the contact through the capillary action of mercury in the mercury tank at the bottom of the tube. In this paper, the wet spring relay is applied to the field of laser control, which is a new application and design for the wet spring relay itself. For the control of laser light wave, as an intermediate medium, it establishes the control relationship between external electrical signal and laser light wave, and realizes the control of laser waveform and waveform period. The scheme is controlled outside the laser light source, has no impact on the characteristics of the laser itself, can reduce the distortion of the laser, and has few requirements on the light source, So that the experimental scheme has general flexibility. At the same time, it also has the advantages of high stability, less distortion of output waveform and low driving power.

The methods of using electrical signals to control laser light waves mostly use the electro-optic effect of the change of refractive index of some crystal materials under the action of external electric field. The main problems of this method are that it requires high driving power, poor stability, light waves are prone to distortion and so on. The wet spring relay has the advantages of no contact jitter and long-term stability, which makes the design system have high stability. As the contact, the tongue reed is sealed in the nitrogen filled glass tube, which also makes the design have better temperature stability. It has the advantages of simple structure, low cost and easy implementation.

1. Basic working principle of wet spring relay

The wet reed relay is an electronic control device, which is composed of a wet reed tube and a driving coil. The structure is shown in Figure 1,

Design of laser light wave control system based on reed relay and electrical signal

The wet reed is the core of the wet reed relay. It is filled with a certain amount of mercury. Relying on the capillary action of the moving reed, the mercury at the lower end of the wet reed can rise, so that the dynamic and static contacts are wetted by the mercury film. When a certain voltage is applied to both ends of the coil, a certain current will flow through the coil, resulting in electromagnetic effect. The moving reed will attract the static reed under the attraction of electromagnetic force, so as to make the moving reed and the static reed close. When the coil is powered off, the electromagnetic suction also disappears, and the moving reed will return to the original position to separate the moving reed from the static reed.

In this experiment, the laser light path is aligned on the right side of the static reed, because the mercury in the wet spring relay rises by the capillary action of the dynamic reed. When the dynamic reed moves to the right side of the static reed and contacts him, the mercury on the dynamic reed contacts the static reed, and the light spot is aligned on the right side of the static reed, which can make the light control speed faster, The light path is blocked by mercury beads attached to the moving reed to obtain a large extinction ratio. When the laser is aligned on the right side of the moving reed, the structure of the wet spring relay is shown in Figure 2. When no voltage is applied at both ends of the coil, the optical path is on. When voltage is applied to the coil, the moving reed is attracted to the static reed, and mercury rises to the contact point between the moving reed and the static reed due to capillary action, so that the optical path is blocked and the optical path is closed. By loading the signal on the coil, the optical path is in the on-off state, so as to realize the control of laser light wave.

2. Experimental system design

2.1 design of optical path

The experimental system needs a collimator to adjust the optical path. The optical fiber collimator is made of tail fiber and self focusing lens. It can convert the transmitted light in the optical fiber into collimated light, or couple the external parallel light to the single-mode optical fiber. In the design, the light spot is located on the right side of the static reed through the collimator. The physical object of the overall experimental platform of collimator and wet spring relay is shown in Figure 3 and Figure 4. The collimator can adjust the height, horizontal position and horizontal angle through the knob, so as to accurately adjust the optical path, so as to achieve the best optical result. At the same time, the wet spring relay is fixed on the adjustable platform, which can also adjust the height, horizontal position and horizontal angle, so as to make the adjustment of the optical path more convenient and precise.

In the light, in order to facilitate the light, you can choose the red laser source for coarse adjustment, and then you can choose any other laser source, which makes the design scheme have less restrictions on the light source, and reflects the flexibility and universality of the experimental scheme. Fine adjustment is carried out through the collimator and the fine adjustment knob on the platform on which the wet spring relay is placed. In the process of adjustment, the optical power of each part of the optical path is measured by a power meter to complete the adjustment of the optical path. In this experiment, a 550 nm wavelength laser source was selected to measure the results.

A signal source is loaded on the coil to control the optical path. The driving voltage used is about 3V. The optical path is controlled by the AC pulse signal source. The frequency of the AC pulse source can be changed to control the laser output optical waveform and the laser optical wave period.

2.2 design of the overall experimental system

As shown in Fig. 5, the experimental system selects a stable 1550nm wavelength laser source as the light source, aligns the optical path through the collimator to make the laser output light align with the right side of the static spring, receives the light through the wet spring relay through another collimator, and adds a light amplifier at the output end of the collimator to make the output light easy to observe on the oscilloscope. The output light of the optical amplifier is connected to the oscilloscope with optical port for detection. The oscilloscope selected in the experimental system is hp83430a. The AC signal source is used to control the of the wet spring relay, and the AC pulse signal source is loaded to both ends of the driving coil of the wet spring relay to realize the control of the reed of the wet spring relay. At the same time, the synchronous clock of the AC pulse signal source is input to the oscilloscope as the trigger clock of the oscilloscope to make the oscilloscope and the control signal source reach the synchronous state. The control signal source is HP 813la.

3. Analysis of experimental results

Because the red laser source is easy to observe, first use the red laser source to roughly adjust the optical path, and then use the 1550nm wavelength laser source as the light source for further measurement. The output optical power of the 1550nm wavelength laser source is 4.01dbm. After light alignment, when there is no wet spring relay in the optical path, the optical power received by the second collimator is 4.99dbm. When the wet spring relay is added to the optical path, the received optical power amplified by EDFA is measured. When the reed of the wet spring relay is not connected and the optical path is in the on state, the received optical power is an 8.43dbm. When the reed of the wet spring relay is connected and the optical path is in the off state, the received optical power is a 13.56dbm and the extinction ratio is 5.1db.

The AC signal source is a periodic pulse signal. When the pulse signal period is different, the output laser waveform and the period are observed. When the selected period is 3MS and the driving voltage is 3V, the signal is loaded on the driving coil of the wet spring relay to control the movement of the reed and mercury of the wet spring relay. When the signal is loaded into the coil, the light passing through the system is controlled by the AC signal source. The waveform controlled by the signal source on the oscilloscope is shown in Figure 6. The control optical period is 3MS, which is the same as the frequency of the AC signal source. Among them, the rise time is 1.65ms, the fall time is 1.35ms, and the optical wave amplitude difference is 1100uw after photoelectric conversion. The waveform is approximately sinusoidal. This is because the sum of rise time and fall time is similar to the period of the signal source, and the whole waveform is composed of rising edge and falling edge.

When the period of AC signal source is 40ms, the driving voltage is 3V. The waveform controlled by the signal source on the oscilloscope is shown in Figure 7. The control optical period is 40ms, which is the same as the frequency of the AC signal source. Among them, the rise time is 1.3ms, the fall time is 1.55ms, and the control depth is 890uw after photoelectric conversion. The waveform is square wave. The period is 40ms. The output waveform is stable, less affected by the outside world, good waveform and low driving voltage, which fully reflects and confirms the advantages of the scheme.

From the above results, it can be concluded that after the light is aligned through the collimator using the wet spring relay as the medium, the external electrical signal can control the laser waveform and period. The waveform can be sine wave, square wave, etc. When the period of the external signal source is 3MS, a sine wave can be obtained. When the external signal is greater than 3MS, the waveform is a square wave. The period of laser light wave is controlled by the signal source, which is the same as the signal source.

4. Conclusion

By analyzing and observing the internal structure of the wet spring relay, the movement of the reed and mercury of the wet spring relay is used to control the optical path. Because the wet spring relay is controlled by the AC signal source, the AC signal source also controls the optical path. The control method has low driving voltage, high stability and good temperature stability. At the same time, there are few restrictions on the requirements of light source, which has universal applicability and flexibility. It has the advantages of simple structure and low price, and has good advantages for further experimental research and product development. At the same time, this paper is also the further research and application of wet spring relay.

Responsible editor: GT

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