激光器驱动电路中英文翻译.docx

中文2540字
Laser driver circuit
Small changes will directly semiconductor laser drive current to the output intensity fluctuation. To stabilize the output power semiconductor laser, Voltage negative feedback principle to design a constant current driving circuit comprises a soft starting and current limiting protection circuit based on; At the same time, according to the need of the light source is modulated to eliminate the influence of background light and, integrated laser modulation circuit comprises a crystal oscillation circuit and divider circuit design. Making the specific circuit and complete the relevant experimental. The experimental results show that the circuit can provide a driving current of high stability, Current stability up to 0.05%; Soft start and current-limiting protection circuit can protect the semiconductor laser and enhance the impact capability. Modulation circuit generates a carrier signal needed for laser diode modulation and direct to complete the output light modulation, The switch can be conveniently realized from 256Hz to 512kHz range of 12 kinds of commonly used modulation frequency selection.
Semiconductor laser with its excellent characteristics, high efficiency, simple structure, small is widely used in scientific research, national defense, medical, and other areas of processing, its drive technology becomes more and more important. Semiconductor laser is the ideal electron - photon direct conversion devices, quantum efficiency is very high, the current small changes will lead to a great change, the output light intensity of the therefore, semiconductor laser drive current requirements is very high. Driving technology of semiconductor laser usually adopts constant current drive mode, this work, through the principle of negative feedback control loop, directly provide the effective control of the drive current. In addition, the transient current or voltage spikes, and overcurrent, overvoltage will damage the semiconductor laser drive circuit, therefore should be considered in the protection circuit against electric shock measures and special.
In some applications, DC semiconductor lasers produce DC drive light in the measurement process is vulnerable to interference from ambient light slow change, which could not be separated from the environment light required DC optical signal, the signal-to-noise ratio is too small, so to carry on the modulation. When the high-speed modulated semiconductor lasers, there will be dynamic characteristics is complex, such as the relaxation oscillation, since the pulse and multi-pulse phenomena. In this paper, experiments were conducted to study the characteristics of low frequency modulation. Semiconductor laser output is stable, and can be directly modulated, it has been widely applied in optical system, is the preferred source sensor system. This paper describes the design of a high stability driving current, modulation, simple operation and low cost driving circuit for the light source of optical fiber systems.
In this paper, the design of driving the semiconductor laser modulation circuit composed of four parts, including constant current circuit, a soft start, current limit protection and modulation signal generating circuit. The constant current circuit to generate a high stable drive current. Soft start is the role of eliminating surge may be present in the circuit, to prevent the harm of surge for laser. To avoid damage due to overcurrent caused by semiconductor laser can not be restored, then adding current-limiting protection in a driver circuit. Circuit to realize the modulation and frequency can be adjusted to generate a modulated signal.
The constant current circuit is shown in figure 1, The in-phase end voltage reference Vr into A1 op amp, the operational control amplifier conducting level, and thus to obtain the corresponding output current. The output current generated by sampling voltage sampling resistor Rs, the sampling voltage is amplified as the inverting input voltage feedback voltage feedback amplifier A1, and voltage and the in-phase input end of comparison, Q2 to adjust the output voltage through the triode, adjustment and output current of semiconductor lasers, so that the whole closed-loop feedback system in the dynamic balance.

Figure 1 Constant current map
Because the switch instantaneous in power supply generates a voltage, current surge, as well as the surge interference effects are likely to cause the breakdown and the damage of the semiconductor laser, and therefore must be in the design of soft start circuit drive laser, namely the use of the charge and discharge of RC circuit, delay time, the specific circuit as shown in Figure 2 as shown in. Switch S1 is closed, the current through the resistor R1 and capacitor C3 to charge, the base electrode of the triode Q voltage gradually rises. As the capacitor charging and the conduction of the triode, output voltage Vo is achieved from 0 to the maximum rise slowly, until the capacitor charge saturation, the voltage and current stabilizing. When the power supply is disconnected, the process of reverse, so as to realize the current and voltage decreases slowly.

Figure 2 Soft start circuit diagram
Laser soft start time and the charging capacitor and the corresponding resistance, when the capacitor charging tends to saturation, the output voltage soft start circuit can achieve maximum. Power supply voltage is V I, the capacitor voltage is Vo, the capacitor charging formula:

According to this formula can calculate the electric charge and discharge time.
Semiconductor laser with other devices, have normal working current, if the current exceeds this range, the laser will be damaged, therefore must restrict current laser in the set range.
Emitter voltage transistor Q2 as the feedback voltage terminal phase in A3 op amp, when the feedback voltage is less than the limit voltage V, A3 op amp output low level, the transistor Q1 is turned on, this time by a triode Q2 output voltage feedback voltage is greater than the limit; when the voltage of V, A3 op amp output high, triode Q1 cutoff, this limits the triode Q2 emission increases very current, and is limited to a specific value. So even if the current caused by Vr control voltage exceeds the set value, the triode Q1 and Q2 are connected in series, so the total current will be clamped in the setting current value.
Modulation signal generating circuit is composed of a crystal oscillating circuit and divider circuit is composed of two parts, used to generate the high stability of frequency, duty cycle square wave signal is stable. Crystal oscillating circuit directly generated by the active oscillator, oscillation frequency is 1MHz. Frequency divider circuit composed of a CMOS integrated circuit 4040.1MHz pulse signal after the frequency by 4040, pin output frequency from the switch is selected, the duty cycle is 50%, amplitude is 5V square wave signal. The modulation frequency dividing frequency were 256Hz, 512Hz, 1kHz, 2kHz,4kHz,8kHz,16kHz,32kHz, 64kHz128kHz, 256kHz, 512kHz..
Driving an important technical parameters of circuit for current stability. Current stability is in a certain period of time, several measurements through the current size of the semiconductor laser, namely the ratio of output current stability for the relative change amount and input current, stability calculation, there will be current relative change is defined as the measurement of the maximum and minimum values, will measure the average value as the input current value.
Drive circuit based on voltage negative feedback principle, by constant current drive mode to realize the control of the injection current and output power of semiconductor laser, and it can provide high stable output current, current stability 0.05%. Drive circuit with soft start, current limit circuit protection, reduce the damage of semiconductor laser to surge breakdown and current, the modulation circuit and the drive circuit effectively combined, realize the frequency is, the development of new technology of optical fiber communication is essential.
The causes of dispersion: One is the light emitted by the light source is not monochromatic light; two is the modulation signal has a certain bandwidth.
The dispersion of the classification: By different modes or different frequency (or wavelength) light signal components, transmission in optical fibers, due to the physical phenomenon of different group velocities cause signal distortion is called fiber dispersion. The fiber dispersion is divided into mode dispersion (or intermodal distortion), material dispersion and waveguide dispersion. After two kinds of dispersion is the dispersion a pattern, also known as intra-modal dispersion.
Dispersion harm: Fiber dispersion in optical signal waveform distortion, performance for the pulse width, it is the time domain characteristics of optical fiber. In digital communication system, pulse broadening of optical signal is an important index. Pulse broadening is too large can cause adjacent pulse gap decreases, the adjacent pulse will overlap and regenerative repeater decision errors occur, which increases the BER, transmission bandwidth narrowing, limit the transmission capacity of optical fiber.
Said method of dispersion: Commonly used dispersion representation has maximum time delay for $S, pulse width R and optical bandwidth of 3dB B three. The maximum time delay difference delay description fiber in the fastest and most slow wave component. Used to describe the effect of fiber dispersion on the transmission signal pulse broadening and optical fiber bandwidth. A section of optical fiber as a network analysis of the dispersion characteristics, the available time domain method and frequency domain method. When in the time domain analysis, dispersion effect is represented by the pulse broadening, and analyzed in the frequency domain, the transmission bandwidth said.

激光器驱动电路
半导体激光器驱动电流的微小变化将直接导致其输出光强的波动。为实现半导体激光器的稳定功率输出,基于电压负反馈原理设计了包含软启动和限流保护电路的恒流驱动电路;同时针对为消除背景光的影响而对光源进行调制的需要,设计了包括晶体振荡电路和分频电路的集成激光器调制电路。制作具体电路并完成了相关实验。实验结果表明该电路能够提供高稳定度的驱动电流,电流稳定度达0.05%;软启动和限流保护电路可保护半导体激光器并提高其抗冲击能力。调制电路产生半导体激光器调制所需的载波信号并直接完成输出光调制,通过开关可方便地实现从256Hz到512kHz范围内12种常用调制频率的选择。
半导体激光器以其超小型、高效率、结构简单等优良特性被广泛应用于科研、国防、医疗、加工等领域,其相应的驱动技术也显得越来越重要。半导体激光器是理想的电子-光子直接转换器件,有很高的量子效率,微小的电流变化都将导致其输出光强的很大变化,因此,半导体激光器的驱动电流要求非常高。半导体激光器的驱动技术通常采用恒流驱动方式,在此工作方式下,通过负反馈原理控制回路,直接提供驱动电流的有效控制。此外,瞬态的电流或电压尖峰脉冲,以及过流、过压都会损坏半导体激光器,因此驱动电路中还应考虑特殊的抗电冲击措施和保护电路。
在一些测量应用中,直流驱动的半导体激光器产生的直流光在测量过程中容易受到缓慢变化的环境光的干扰, 导致无法从环境光中分离出所需直流光信号, 本文系统信噪比过小,因此要对其进行调制。当半导体激光器进行高速调制时, 会出现很复杂的动态特性,如驰豫振荡、自脉动以及多脉冲等现象。本文对其低频调制特性进行了实验研究。半导体激光器输出有足够的稳定性,且可直接调制, 它已在光纤系统中得到普遍应用,是传感器系统的首选光源。本文为光纤系统的光源设计了一种高稳定度驱动电流、可调制、操作简单且成本低廉的驱动电路。
本文设计的半导体激光器驱动调制电路由四大部分组成,包括恒流电路、软启动、限流保护和调制信号产生电路。恒流电路产生高稳定度驱动电流。软启动的作用是消除电路中可能存在的浪涌,防止浪涌对激光器的危害。为避免由于过流等因素引起半导体激光器不可恢复的损坏,则在驱动电路中加入限流保护。调制信号产生电路实现调制和频率可调。
实际的恒流电路见图1,基准电压Vr送入运放A1的同相端,该运放控制放大器的导通程度,并由此获得相应的输出电流。该输出电流通过取样电阻Rs产生取样电压,该取样电压经放大后作为反馈电压反馈回电压放大器A1的反相输入端,并与同相输入端的电压比较,通过三极管Q2对输出电压进行调整,进而对半导体激光器的输出电流进行调整,使整个闭环反馈系统处于动态的平衡中。

图1 恒定电流图
由于在电源开关开启的瞬间会产生电压、电流浪涌冲击,以及外界干扰产生的浪涌影响都有可能造成半导体激光器的击穿和损坏,因此必须在激光器驱动电路中设计软启动电路,即利用RC电路的充放电,实现时间上的延迟,具体电路如图2所示。开关S1闭合后,电流经电阻R1向电容C3充电,三极管Q基极电压逐渐升高。随着电容的充电以及三极管的导通, 输出电压Vo实现了从0到最大的缓慢上升, 直到电容充电饱和后,此时电压和电流趋于稳定。当电源断开时,上述过程反向, 从而实现电流和电压的缓慢下降。

图2 软启动电路图
激光器的软启动时间与充电电容和相应电阻有关,当电容充电趋于饱和时, 软启动电路的输出电压可以达到最大。设电源电压为Vi,电容电压为Vo,电容充电公式为:

根据此公式可以计算电路充放电的时间。
半导体激光器同其他器件一样,都有正常工作电流,如果电流超过这个范围,激光器将会被损坏,因此必须把激光器的工作电流限制在设定范围内。
三极管Q2的发射极电压作为反馈电压加在运放A3的同相端,当反馈电压小于限制电压V时,运放A3输出低电平,三极管Q1管导通,此时由三极管Q2输出电压;当反馈电压大于限制电压V 时,运放A3 输出高电平,三极管Q1截止,此时限制了三极管Q2 发射极电流的增加,而被限制在某一特定值上。因此即使控制电压Vr 所引起的电流超过设定值,又由于三极管Q1和Q2是串联在一起的,所以总的电流就会被箝制在设定电流值上。
调制信号产生电路由晶体振荡电路和分频电路两部分组成,用于产生频率稳定度高,占空比稳定的方波信号。晶体振荡电路直接由有源晶振产生,振荡频率为1MHz。分频电路由CMOS 集成电路4040实现。1MHz脉冲信号经4040分频后,从开关选中的管脚输出一定频率,占空比为50% ,幅值为5V的方波信号。经分频后的调制频率分别为256Hz,512Hz,1kHz,2kHz,4kHz,8kHz,16kHz,32kHz,64kHz128kHz, 256kHz,512kHz。
驱动电路一个重要技术参数为电流稳定度。电流稳定度是在一定时间内,多次测量通过半导体激光器的电流大小,即稳定度为输出电流的相对变化量与输入电流的比值, 进行稳定度计算,这里将电流相对变化定义为测量最大值与最小值之差,将测量平均值作为输入电流值。
驱动电路基于电压负反馈原理,通过恒流驱动方式实现了对半导体激光器注入电流和输出光强的控制,并能够提供高稳定度的驱动电流, 电流稳定度0.05%。驱动电路中加入了软启动、限流保护等辅助电路,减少了由于浪涌击穿和过电流导致的半导体激光器的损坏,同时将调制电路和驱动电路有效地结合起来,实现了频离,发展新型光纤通信技术都是至关重要的。
色散的原因: 一是光源发出的光并不是单色光;二是调制信号有一定的带宽。
色散的分类: 由不同模式或不同频率( 或波长) 成分组成的光信号,在光纤中传输时,由于群速度不同而引起信号畸变的物理现象称为光纤的色散。光纤的色散分为模式色散( 或模间畸变)、材料色散以及波导色散。后两种色散是某一模式本身的色散,也称模内色散。
色散的危害: 光纤的色散导致光信号的波形失真,表现为脉冲宽度,它是光纤的时域特性。对于数字通信系统来讲,光信号的脉冲展宽是一项重要的指标。脉冲展宽过大就会引起相邻脉冲间隙减小,相邻脉冲将会产生部分重叠而使再生中继器发生判决错误,从而使误码率增加,传输频带变窄,限制了光纤的传输容量。
色散的表示方法: 常用的色散表示方法有最大时延差用以$S, 脉冲展宽R和光纤3dB带宽B三种。最大时延差描述光纤中速度最快和最慢光波成分的时延之差。脉冲展宽和光纤带宽用以描述光纤色散对传输信号的影响。将一段光纤看作一个网络,可用时域法和频域法分析其色散特性。当在时域分析时,色散影响用脉冲展宽表示,而在频域分析时,则采用传输带宽表示。

9